A NEAR REAL-TIME BERYLLIUM MONITOR WITH
CAM AND WIPE ANALYSIS CAPABILITIES
FINAL REPORT
Written By:
D.T. Kendrick & Steven Saggese, Ph.D.
Submitted:
December 2002
DOE Contract # DE-AC26-00NT40768
Submitted To:
Ron K. Staubly
U.S. Department of Energy
National Energy Technology Laboratory
P.O. Box 880
3610 Collins Ferry Road
Morgantown, WV 26507-0880
Submitted By:
Science & Engineering Associates, Inc.
6100 Uptown Blvd., NE
Albuquerque, NM 87110
A NEAR REAL-TIME BERYLLIUM MONITOR WITH
CAM AND WIPE ANALYSIS CAPABILITIES
FINAL REPORT
Written By:
D.T. Kendrick & Steven Saggese, Ph.D.
Submitted:
December 2002
DOE Contract # DE-AC26-00NT40768
Submitted To:
Ron K. Staubly
U.S. Department of Energy
National Energy Technology Laboratory
P.O. Box 880
3610 Collins Ferry Road
Morgantown, WV 26507-0880
Submitted By:
Science & Engineering Associates, Inc.
6100 Uptown Blvd., NE
Albuquerque, NM 87110
Science & Engineering Associates, Inc.
Final Report
DISCLAIMER
This report was prepared as an account of work sponsored by an agency of the United
States Government. Neither the United States Government nor any agency thereof, nor
any of their employees, makes any warranty, expressed or implied, or assumes any legal
liability or responsibility for the accuracy, completeness, or usefulness of any
information, apparatus. Product, or process disclosed, or represents that its use would not
infringe privately owned rights. Reference herein to any specific commercial product,
trademark, manufacturer, or otherwise does not necessarily constitute or imply its
endorsement, recommendation, or favoring by the United States Government or any
agency thereof. The views and opinions of the authors expressed herein do not
necessarily state or reflect those of the United States Government or any agency thereof.
ABSTRACT
Science & Engineering Associates, Inc. (SEA), under contract # DE-AC26-00NT40768,
was tasked by the US Department of Energy – National Energy Technology Laboratory
to develop and test a near real-time beryllium monitor for airborne and surface
measurements. Recent public awareness of the health risks associated with exposure to
beryllium has underscored the need for better, faster beryllium monitoring capabilities
within the DOE. A near real-time beryllium monitor will offer significant improvements
over the baseline monitoring technology currently in use. Whereas the baseline
technology relies upon collecting an air sample on a filter and the subsequent analysis of
the filter by an analytical laboratory, this effort developed a monitor that offers near realtime measurement results while work is in progress. Since the baseline typically only
offers after-the- fact documentation of exposure levels, the near real-time capability
provides a significant increase in worker protection.
The beryllium monitor developed utilizes laser induced breakdown spectroscopy, or
LIBS as the fundamental measurement technology. LIBS has been used in a variety of
laboratory and field based instrumentation to provide real-time, and near-real-time
elemental analysis capabilities. LIBS is an analytical technique where a pulsed high
energy laser beam is focused to a point on the sample to be interrogated. The high energy
density produces a small high temperature plasma plume, sometimes called a spark. The
conditions wit hin this plasma plume result in the constituent atoms becoming excited and
emitting their characteristic optical emissions. The emission light is collected and routed
to an optical spectrometer for quantitative spectral analysis. Each element has optical
emissions, or lines, of a specific wavelength that can be used to uniquely identify that
element. In this application, the intensity of the beryllium emission is used to provide a
quantitative measure of the abundance of the element in the sample.
The monitor can be operated in one of two modes, as a continuous air monitor (CAM), or
as a wipe monitor. In its CAM mode, the monitor collects an air sample for a user
programmable sampling time on a conventional mixed cellulose ester (MCE) filter. The
monitor can also be used in a wipe analysis mode, where the user can load up to 60
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previously collected wipe samples, typically obtained on 47 mm filter media, into
disposable filter cassettes.
Under this effort, a beryllium monitor was designed, fabricated and tested. During
laboratory testing, the monitor’s measurement performance met the stated measurement
objectives at the outset of the project. A typical minimum detectable beryllium mass for
the monitor is below the 0.2 mg/m^3 goal of the project. Field-testing of the monitor
show it to exhibit extremely good sensitivity to very low levels of beryllium. On a per
spark basis, the monitor has been shown to be capable of detecting a few tens of
picograms of beryllium. At the culmination of the project, the beryllium CAM unit was
delivered to the U.S. DOE-Rocky Flats Environmental Management Site where it is
undergoing additional on-site evaluations.
ACKNOWLEDGEMENTS
This development effort was funded under the Industry Program through the National
Energy Technology Laboratory (NETL) under contract DOE Contract # DE-AC2600NT40768. SEA gratefully acknowledges the support and contributions of Mr. Ron K.
Staubly, the technical contact for NETL, Dr. Adam Hutter, the technical representative
from the U.S. Department of Energy Environmental Measurements Laboratory,
representing the CMST program, and Dr. Stephan Weeks from the U.S. Department of
Energy Special Technologies Laboratory. SEA also wishes to extend thanks to Dr. Mark
Hoover of the National Institute of Occupational Health for his many technical
contributions and suggestions and for providing the size selected particulate beryllium
material used in the calibration and evaluation of the prototype monitor. SEA also
wishes to extend a special thanks to the many technical contributions provided from the
U.S. DOE Rocky Flats Environmental Technology Site (RFETS) and the U.S. DOE
Pantex Plant. In particular SEA wishes to thank Mr. Brett Claussen, Mr. Alec Cameron,
and Ms. Rae Eklund of RFETS for their technical input during the design process and
support during the demonstration activities. Mr. Jeffery Yokum, Mr. Gary Cockrell, Mr.
Shane Laurent, and Dr. Richard Copeland of Pantex provided valuable technical input.
SEA also gratefully acknowledges the support provided by the Lovelace Respiratory
Research Institute, and in particular the efforts of Tom Holmes.
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EXECUTIVE SUMMARY
Science & Engineering Associates, Inc. (SEA), under contract # DE-AC26-00NT40768,
has been tasked by the US Department of Energy – National Energy Technology
Laboratory to develop and test a near real-time beryllium monitor for airborne and
surface measurements. Recent public awareness of the health risks associated with
exposure to beryllium has underscored the need for better, faster beryllium monitoring
capabilities within the DOE. A near real- time beryllium monitor will offer significant
improvements over the baseline monitoring technology currently in use. Whereas the
baseline technology relies upon collecting an air sample on a filter and the subsequent
analysis of the filter by an analytical laboratory, this effort developed a monitor that
offers near real-time measurement results while work is in progress. Since the baseline
typically only offers after-the-fact documentation of exposure levels, the near real-time
capability provides a significant increase in worker protection.
This photo shows the completed beryllium monitor
The beryllium monitor utilizes laser induced breakdown spectroscopy, or LIBS as the
fundamental measurement technology. LIBS has been used in a variety of laboratory and
field based instrumentation to provide real-time, and near-real-time elemental analysis
capabilities. LIBS is an analytical technique where a pulsed high energy laser beam is
focused to a point on the sample to be interrogated. The high energy density, typically
GW/cm2 , produces a small high temperature plasma plume, sometimes called a spark.
The conditions within this plasma plume result in the constituent atoms becoming excited
and emitting their characteristic optical emissions. The emission light is collected and
routed to an optical spectrometer for quantitative analysis. Each element has optical
emissions, or lines, of a specific wavelength that can be used to uniquely identify that
element. In a LIBS application, the intensity of the emission is used to provide a
quantitative measure of the abundance of the element in the sample under interrogation.
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A typical LIBS system is comprised of a high energy, pulsed infrared laser, and an
optical system to deliver the laser beam to the sample under interrogation where it is
focused to a small spot, 0.8 mm in diameter in the case of the beryllium monitor. Optical
emissions from the plasma are sampled by another optical system and routed to an optical
spectrometer, usually equipped with a scientific grade charge-coupled detector (CCD) or
a photodiode array (PDA) for quantitative measurement. This monitor utilizes the 313
nm beryllium emission line for quantitative analysis.
The major LIBS components used in the beryllium monitor developed under this contract
include:
• CFR 200 Nd:YAG laser, manufactured by Big Sky Laser,
• 250 IS, imaging spectrograph, manufactured by Chromex Inc.,
• Model DB420-OE CCD, manufactured by Andor Technology, Inc.,
• A custom co- linear optics system to both deliver the laser light and collect the
emission light.
The monitor can be operated in one of two modes, as a continuous air monitor (CAM), or
as a wipe monitor. In its CAM mode, the monitor collects an air sample fo r a user
programmable sampling time on a conventional mixed cellulose ester (MCE) filter. The
filters are held in disposable filter cassettes. A robotic arm is used to move the filter
cassettes from a storage carousel to an air sampling station, where the air sample is
collected. Following collection of the air sample, a filter cassette is again moved to the
LIBS analysis station for quantitative analysis.
The filter cassette is placed in a spark chamber positioned under the laser delivery optics.
The spark chamber is mounted on a pair of X-Y stages that allow it to be moved in a
circular fashion under the fixed position of the laser beam by the robotic arm. The
motion consists of a series of concentric circular “orbits” starting at the center of the filter
circle and moving outward. In this manner, the entire exposed area of the filter media
can be interrogated for beryllium content. This scheme also allows the monitor to use
either 47 mm diameter filter media, or 25 mm diameter media. Following the LIBS
analysis, the filter cassette is removed from the spark chamber by the robotic arm, and
placed in the spent filter receptacle for eventual disposal as beryllium waste.
The system timing in the CAM mode allows a new filter to be acquiring a sample,
typically 10-15 minute sampling interval, while the LIBS analysis and disposal of the
previous sample is completed, allowing nearly continuous sampling. The filter carrousel
has a capacity of 60 filters, including provisions for 5 spiked samples, and 5 blank
samples. This allows continuous unattended operation in the CAM mode of up to four
hours. The CAM mode also supports a real-time alarm. The alarm set point is user
selectable, and is activated when a sample analysis result exceeds the preset alarm trigger
level.
In its wipe analysis mode, the user loads previously collected wipe samples, typically
obtained on 47 mm filter media, into the filter cassettes. The filter cassettes containing
the samples are then loaded into the removable filter carrousel. The 60-sample capacity
of the filter carrousel is arranged in five columns of 12 cassettes each. The bottom most
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slot in each column is reserved for spiked samples, and the top slots are reserved for
blanks. In the wipe analysis mode the air-sampling step is omitted, and the robot moves
the filter cassettes in sequence from the carousel directly to the LIBS analysis station.
As soon as the LIBS analysis of a sample has been completed, the spectral data is
reduced, and a result is posted to the display screen. In the case of the wipe samples the
result is given in units of micrograms (µg) per filter. In the CAM mode the result is
given in the units of micrograms per cubic meter of air (µg/m3 ). During sampling a
thermal mass flow meter is used to integrate the total flow volume acquired on the filter.
An external temperature sensor, and a barometric pressure sensor within the flow meter
are used to convert the flow volume from a mass volume to a true volumetric total flow
volume. The measured beryllium mass is simply divided by the total flow volume to
provide the conventional units of µg/m3 . The air sampling rate depends somewhat upon
the elevation at which the monitor is used, but is nominally 50 liters per minute (LPM).
A principal consideration throughout the evolution of the design concept into the physical
instrument was contamination control. It was understood that to be useful, the monitor
must be able to be operated in radiologically contaminated areas, as well as areas
contaminated with beryllium. A number of design features were incorporated to ensure
that the monitor would be adequately protected from external contamination, including
airborne particulate contamination. Additionally, the monitor design includes features to
protect the environment in which it is operated from potential releases of beryllium from
samples within the monitor during the LIBS analysis.
Calibration of the monitor consists of developing a mathematical relationship between
the intensity of the 313 nm line and the total beryllium mass on a filter. A principal
components analysis (PCA) technique is employed to extract the spectral information
related to beryllium, and a least squares regression is used to fit the beryllium component
metric to beryllium mass. To calibrate the instrument the user prepares a series of
samples spiked with known masses of beryllium, analyzes them in the monitor using the
conventional user interface software. The resulting data files are then reprocessed by a
separate calibration data analysis software package resulting in a calibration file. This
calibration file contains the necessary parameters to allow the spectral processing
algorithm to reduce the spectra to a beryllium mass in real time during the monitor
operation. The user may develop multiple calibration files and select a particular file to
be used by the monitor for a given analysis sequence. Additionally the spectral data
resulting from every analysis run is stored on a hard disk within the instrument, and can
be later reprocesses with the same, or a different calibration file. The raw and processed
results data are easily recovered from the monitor via an external network connection to
the embedded computer within the monitor.
Overall the monitor’s measurement performance is acceptable relative to the stated
measurement objectives at the outset of the project. A typical minimum detectable
beryllium mass for the monitor is below the 0.2 µg/m3 target. The monitor calibration is
dependent upon the particulate size of the beryllium collected on the filters. Larger
particles exhibit lower emission line intens ity per unit beryllium mass than do smaller
particle sizes. The monitor response was evaluated over a particle size range from
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particles less than 0.5 microns aerodynamic diameter to particles greater than 5.9 microns
in aerodynamic diameter. Consequently it is recommended that the users either
characterize the particulate size of airborne beryllium particulates in the monitoring
environment, and calibrate the monitor with a similar particulate size, or use an
appropriately conservatively large particulate size. Calibration and subsequent fieldtesting of the monitor show it to exhibit extremely good sensitivity to very low levels of
beryllium. On a per spark basis, the monitor has been shown to be capable of detecting a
few tens of picograms of beryllium.
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TABLE OF CONTENTS
Disclaimer .............................................................................................................................i
Abstract .................................................................................................................................i
Acknowledgements ............................................................................................................. ii
Executive Summary........................................................................................................... iii
Table of Contents.............................................................................................................. vii
Table of Figures ............................................................................................................... viii
Table of Tables....................................................................................................................ix
1
Introduction................................................................................................................. 1
1.1
Technology Need ................................................................................................ 1
1.2
LIBS Background ............................................................................................... 1
2
Requirements Analysis ............................................................................................... 5
2.1
Design Report ..................................................................................................... 5
2.2
Direct Surface Interrogation Capability.............................................................. 5
3
Method Development .................................................................................................. 8
3.1
Spectral Region Selectio n ................................................................................... 8
3.2
Filter Media Selection....................................................................................... 13
3.3
Internal Standard Evaluation............................................................................. 14
3.4
Sample Preparation Techniques........................................................................ 16
4
System Design........................................................................................................... 20
4.1
Hardware Design............................................................................................... 20
4.2
System Control Software (BeCAMApp.exe) ................................................... 54
5
System Calibration.................................................................................................... 60
5.1
LIBS Calibration............................................................................................... 60
5.2
Flow Measurement Calibration......................................................................... 74
5.3
Air Temperature Calibration............................................................................. 74
5.4
Air Sampling Inlet Calibration.......................................................................... 76
6
Demonstration Measurements................................................................................... 79
6.1
Measurements At LRRI .................................................................................... 79
6.2
Analysis of Demonstration Results................................................................... 80
6.3
Summary of the LRRI Measurement Results ................................................... 95
7
SUMMARY.............................................................................................................. 98
Appendix A – Design Report.............................................................................................. 1
Appendix B – User’s Guide ................................................................................................ 1
Appendix C – Engineering Documentatiion....................................................................... 1
Appendix D: Software Code ............................................................................................... 1
Appendix E – Demonstration Test Plan for RFETS ........................................................... 1
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TABLE OF FIGURES
Figure 1-1: Typical components of a LIBS system ........................................................... 2
Figure 1-2: Typical spectrum from a wipe sample ............................................................ 3
Figure 1-3: Example of the variation in emission intensity with beryllium abundance .... 4
Figure 3-1: Evaluation spectra for the 313 nm spectral region. ......................................... 9
Figure 3-2: Evaluation spectra for the 332 nm spectral region. ....................................... 10
Figure 3-3: Evaluation spectra for the 436 nm spectral region. ....................................... 10
Figure 3-4: Evaluation spectra for the 467 nm spectral region. ....................................... 11
Figure 3-5. Plot of LIBS spectra from RFETS Sample BB06 & simulated spectra. ....... 12
Figure 3-6: Photos of RW-19 filter media following LIBS analysis. .............................. 14
Figure 3-7: Example spectra for lanthanum as an internal standard................................ 15
Figure 3-8: Filter cassettes, used to support the filters during sample preparation ......... 17
Figure 3-9: Filters prepared using the 2.5 – 5.9 µm beryllium particulate suspension.... 19
Figure 4-1: The Canberra filter cassettes utilized in the prototype monitor design......... 22
Figure 4-2: Whatman-41A sample before (left) & after (right) drop test. ........................ 27
Figure 4-3: Oscillations in the spectral baseline showing a correlation with orbit.......... 30
Figure 4-4: Simplified block diagram of the SPARK I.D.™ Beryllium Monitor. .......... 34
Figure 4-5: Drawing of the overall layout of the monitor enclosure ............................... 38
Figure 4-6: Cut-away view of the Instrumentation Module. ........................................... 39
Figure 4-7: Cut-away view of the monitor viewed from the left-hand side .................... 40
Figure 4-8: Photo of the right hand side of the monitor with the panels removed .......... 41
Figure 4-9: Caution label affixed to all operator removable access panels ..................... 42
Figure 4-10: Schematic of the air sampling station ......................................................... 42
Figure 4-11: TSI Model 4043 thermal mass Flowmeter.................................................. 43
Figure 4-12: Components of the LIBS column................................................................ 44
Figure 4-13: Diagram of co- linear optical system. .......................................................... 45
Figure 4-14: Removable laser focusing lens.................................................................... 46
Figure 4-15: Spark chamber ventilation diagram. ........................................................... 47
Figure 4-16: Block diagram of the SX28 microcontroller and associated components .. 49
Figure 4-17: Laser / CCD detector timing diagram. ........................................................ 50
Figure 4-18: Filter cassette carousel used in the monitor. ............................................... 51
Figure 4-19: Spent filter receptacle used in the monitor.................................................. 52
Figure 4-20: Generalized air flow schematic for the monitor enclosure ......................... 53
Figure 4-21: Start screen of the system control software. ............................................... 55
Figure 4-22: System state transition diagram. ................................................................. 57
Figure 4-23: Sample handling state transition diagram. .................................................. 58
Figure 4-24: Software task relationships. ........................................................................ 59
Figure 5-1: Contour plot of beryllium surface distribution. ............................................ 61
Figure 5-2: Three-dimensional plot of beryllium surface distribution. ........................... 62
Figure 5-3: Spark series plot of Beryllium emission line intensity. ................................ 62
Figure 5-4: All spectra from a sample plotted on a single axis. ...................................... 63
Figure 5-5: Mean and standard deviation spectra for a calibration sample. .................... 63
Figure 5-6: Sample-sparking pattern. .............................................................................. 64
Figure 5-7: Average LIBS spectra of calibration samples. .............................................. 66
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Figure 5-8: Expanded view of calibration samples in the Be spectral region. ................ 66
Figure 5-9: Second principal component for 1.020 µg data set. ...................................... 67
Figure 5-10: PC2 score for each single spark spectrum. ................................................. 67
Figure 5-11: Calibrated spark series plot. ........................................................................ 68
Figure 5-12: PRESS result from PLS regression. ............................................................ 69
Figure 5-13: Regression coefficients for 11 latent variable PLS model. ......................... 69
Figure 5-14: Estimated versus actual Beryllium mass for PLS model. ........................... 70
Figure 5-15: Correlation plot for skew and bias corrected model. .................................. 71
Figure 5-16: Correlation plot with error bars for Beryllium Analyzer calibration. ......... 72
Figure 5-17: Top level automated data analysis block diagram. ..................................... 73
Figure 5-18: Photo showing the voltage measurement points for TX92-1 calibration. ... 75
Figure 5-19. The Omega TX92-1 RTD transmitter (4-20 mA Current Loop). ............... 76
Figure 5-20: Photo of inlet nozzle efficiency test configuration. .................................... 76
Figure 6-1: Plot of the results for the Measurement Performance Samples .................... 85
Figure 6-2: Laboratory results for the Synthetically Contaminated Wipe Samples ........ 89
Figure 6-3: Monitor results for the Synthetically Contaminated Wipe Samples ............. 92
Figure 6-6: Variation in instrument response with beryllium particle size. .................... 96
Figure 7-1: Photo of the completed beryllium monitor ................................................... 98
TABLE OF TABLES
Table 3-1: principal Be Emission Lines Considered .......................................................... 8
Table 3-2: Cyclone stage and corresponding aerodynamic size range of the particulate
beryllium ................................................................................................................... 18
Table 4-1: Mass Change Results for drop tests ............................................................... 27
Table 5-1: Beryllium Calibration Sample Data ............................................................... 65
Table 5-2: Temperature settings available on Altek Model 11-250 and corresponding
terminal voltages....................................................................................................... 75
Table 5-3: Inlet nozzle collection efficiency measurement results.................................. 77
Table 6-1: Measurement performance samples ............................................................... 79
Table 6-2: Beryllium mass loadings for synthetically contaminated wipe samples ........ 80
Table 6-3: Measurement results of the Performance Samples......................................... 81
Table 6-4: Statistical summary of the laboratory results of the Performance Samples ... 84
Table 6-5: Statistical summary of the prototype monitor results compared with the
pooled laboratory results ........................................................................................... 84
Table 6-6: Measurement results of the Synthetically Contaminated Wipe Samples ....... 88
Table 6-7: Statistical summary of the results from Assaigai Lab and Johns Manville Lab
for the Synthetically Contaminated Wipe Samples .................................................. 90
Table 6-8: Statistical summary of the results from Assaigai Lab and DataChem Lab for
the Synthetically Contaminated Wipe Samples ........................................................ 90
Table 6-9: Statistical summary of the results from Johns Manville Lab and DataChem
Lab for the Synthetically Contaminated Wipe Samples ........................................... 91
Table 6-10: Comparison of variability by laboratory for the Synthetically Contaminated
Wipe Samples ........................................................................................................... 91
Table 6-11: Results of RFETS Duplicate Samples .......................................................... 94
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1 INTRODUCTION
1.1 Technology Need
The adverse health effects of exposure to airborne beryllium are well known. Personnel
exposure to beryllium during clean- up activities or during material processing is a major
health risk within the DOE, DOD, and some private sector industries. Present laboratorybased technologies for evaluating the concentration of airborne and surface beryllium do
not provide the real- time analysis required to effectively protect workers.
In response to this need, Science & Engineering Associates, Inc. (SEA) proposed, and
has developed a multi- function beryllium monitor based on laser induced breakdown
spectroscopy (LIBS). This system provides the capability to conduct continuous air
monitoring for beryllium, and analyze swipe or smear samples to detect beryllium
contamination on surfaces and equipment.
Measurement results obtained during calibration activities, and during demonstrations
show that the prototype can detect airborne beryllium to levels less than 0.2 mg/m3, and
measurements of surface contamination to less than 0.2 mg/100 cm2 for swipe samples.
The instrument operates in a fully automated mode for the continuous air monitoring
function, and the swipe sample analysis mode. The system also provides an alarming
function, with the trigger level set by the operator.
1.2 LIBS Background
Hardware:
Laser induced breakdown spectroscopy (LIBS) is an analytical technique
well suited to screening level measurements of a wide variety of elemental contaminants.
Recent advances in critical hardware components, primarily compact lasers, detectors and
spectrometers, has made the LIBS technique even more attractive for industrial and
environmental analysis.
Regardless of the deployment technique, all LIBS systems contain the same basic
components. As shown in figure 1-1, a LIBS system consists of a laser source to produce
the plasma, a method of delivering and focusing the laser beam onto the sample, emission
collection optics, a spectrometer to spectrally resolve the emission spectrum, an array
detector for simultaneous measurements of emission intensities over a range of
wavelengths, a trigger to coordinate the laser pulse and the temporal measurement
window of the detector, and a computer to conduct equipment control, data acquisition,
and data analysis.
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Figure 1-1: Typical components of a LIBS system
An emission spectrum is obtained by focusing the high power laser on the sample surface
to produce a local plasma. The surface will absorb the laser pulse, heat rapidly, reduce to
elemental form, and become electronically excited. When the input pulse is removed, the
excited electrons drop to lower energy levels with the emission of characteristic photons.
Elemental analysis is conducted by observation of the wavelength and intensity of the
emission lines.
Beryllium Analysis: When evaluating samples for beryllium content the spectrograph is
tuned to a region that will include both the 313 and 334 nm emission lines. Figure 1-2
shows a LIBS spectra of a wipe sample on a filter with beryllium present. The major
peaks have been labeled with the symbol for the element producing the peak. Note the
major beryllium emission line at 313 nm.
Ti
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LIBS Result = 0.247µg Be for this swipe sample
Ti
Ti
Ti
Fe
Ti
Be
Ti
Cu
Cu
Ti
Ca
Fe
Al
Ca
Ti
Fe
Figure 1-2: Typical spectrum from a wipe sample
Calibration: The basis for quantitative analysis with LIBS is that the intensity of the
analyte emission peak is proportional to the abundance of beryllium on the filter to be
analyzed. Thus a larger amount of beryllium produces a larger emission peak.
Calibration of the technique then relies on developing a relationship between the analyte
peak intensity and beryllium abundance. Figure 1-3 shows the variation of the principal
beryllium emission line, at 313 nm, with changing beryllium mass on a filter.
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Figure 1-3: Example of the variation in emission intensity with beryllium
abundance
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2 REQUIREMENTS ANALYSIS
2.1 Design Report
In order to ensure that SEA would develop a prototype instrument that would be useful to
the end user, Rocky Flats Environmental Technology Site, the SEA design team solicited
input to the design from RFETS personnel, as well as technical oversight personnel from
the DOE Environmental Measurements Laboratory and the DOE Special Technologies
Laboratory. The interchange of information between SEA and these various groups was
initiated at the project kick-off meeting, held in Morgantown WV, where SEA presented
its design approach for the prototype monitor to the various affected parties. This began
a process of information exchange between SEA and the various technical representatives
that culminated in the preparation and review of a Design Report that detailed the
approach to be taken in designing and fabricating the prototype monitor. This design
report is included in Appendix A of this report.
2.2 Direct Surface Interrogation Capability
During the process of developing the design report, it was determined that one aspect of
the proposed monitor would pose a number of significant technical challenges. This was
the capability of the monitor to directly interrogate surfaces for beryllium. Through a
series of discussions and written exchanges between SEA and the various DOE technical
representatives, it was eventually decided that this feature of the prototype should be
differed to a later time so that the available resources could be more efficiently applied to
the basic capabilities of the prototype monitor, namely the CAM and wipe analysis
capabilities.
The following gives a summary of the issues associated with development of a direct
surface analysis capability using LIBS. Three major areas are discussed: Calibration,
laser safety, and sample throughput.
2.2.1 Calibration Issues
Although the principle of using LIBS to directly interrogate a surface for beryllium is
relatively straightforward, the devil is in the details, as the saying goes. In a surface
analysis mode the laser is interacting with the surface directly and the composition of the
surface will impact the LIBS analysis methodology that must be used. In essence each
and every different surface upon which the Surface Analysis Module is expected to
perform measurements will require a separate calibration. The process of calibration is
not trivial. It will necessarily include developing a means of delivering a well-quantified
aliquot of beryllium particles to a standard geometry comprised of the particular surface
material. Additionally the LIBS emission characteristics of the particular composition of
the surface must be characterized to ensure that the calibration model used can
accommodate any spectral interference. Ultimately, this would require effort on the part
of the end- user to develop the calibration standards required for their specific application,
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much like is required for other analytical techniques. From the end-user perspective, they
will incur cost for the labor and materials to calibrate the unit for a site-specific substrate.
2.2.2 Laser Safety
Unlike the laser system in the CAM/Wipe Analysis module, the laser system in the
Surface Analysis Module cannot be completely enclosed; it must be able to be directed
against the surface to be interrogated. If the system were restricted to one type of surface
geometry, say a flat surface, then an adequate optical shielding system and laser interlock
could be designed to allow the system to be operated without requiring the operator to
use laser protective eyewear. But if the Surface Analysis Module were used on a surface
with other than a flat geometry, say the curved surface of a pipe, the optical seal may be
defeated, possibly allowing the high-energy laser radiation to escape. In general it is
relatively easy to design and fabricate an optical shield for any particular surface
geometry, but nearly impossible to design and fabricate one that would accommodate all
possible surface geometry’s that could be encountered in the D&D environment.
Therefore, the only reasonable approach would be to require laser protective eyewear for
the operator and any bystanders. This may or may not be a significant limitation of the
system design at the various sites. SEA’s experience with other DOE sites is that
handheld lasers are a major safety concern, regardless of the safety mechanisms built into
the unit or the power of the laser. Thus, specialized laser safety training would likely be
required for the users of the handheld unit. Moreover, there may be a limitation on other
types of D&D activities that could be ongoing during periods of instrument use.
2.2.3 Sample Throughput
In order to acquire the data necessary for the detection limits desired, the hand-held unit
would need to spark the surface of interest at least 10x. Under the method development
for the hand-held system, the specific number for a painted metal surface would have be
determined. Depending upon the outcome of that study, the number of sparks may be
substantially more. What this means to the user is that a trained technician will spend
several to ten minutes preparing the surface, acquiring sparks, and cleaning the touch
probe to minimize cross contamination for each sampling location. Due to laser safety
considerations and ease of instrument use, this operation will probably take two people.
It can be argued that surfaces can be sampled using wipes and the wipes analyzed for
beryllium using the wipe analysis capability of the monitor. The only advantage that a
direct surface analysis has over wipe sampling is if the beryllium were fixed to the
surface, and therefore not available to be transferred to the wipe. But this capability
comes at a huge price in terms of calibration complexity and laser safety issues.
Another perspective involved in the decision to defer development of the direct surface
interrogation capability was the inherent compromises in other areas of system
performance that would result from its incorporation into the overall system design. For
example, incorporation of the Surface Analysis Module requires that the operator be able
to reconfigure the optical input to the spectrometer from either the CAM/Wipe Analysis
Module to the Surface Analysis Module. To accommodate the necessary contamination
control features desired by the end users, this requires a break in the fiber optic between
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the collection optics and the spectrometer input, and further requires that a portion of the
fiber optic be mounted outside of the instrument enclosure. Even with appropriate
coupling optics used at this fiber optic junction, there will be measurable light loss
resulting in higher detection limits. Furthermore the exposed fiber optic incurs an
increased risk of being damaged, increasing the likelihood of instrument down time.
Without the Surface Analysis Module, the fiber optic connecting the emission collection
optics in the CAM/Wipe Analysis Module could be a single continuous fiber bundle that
is routed completely within the instrument enclosure.
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3 METHOD DEVELOPMENT
The objectives of the method development effort were to:
• Identify the best spectral region to use for the optical emission analysis,
• Identify the best filter media to use for the CAM and wipe analysis modes,
• Evaluate the usefulness of an internal standard for reducing spark-to-spark
variability inherent in LIBS and select the best internal standard,
• Identify the optimal parameters for laser-sample interaction.
3.1 Spectral Region Selection
Beryllium exhibits a number of optical emission lines that could potentially be used for
LIBS analysis. The utility of a particular emission line depends upon its relative intensity
and potential for spectral overlap with emission lines from both the filter media used to
collect the sample, and the ambient dust and other particulates that will also be collected
during sampling.
Four spectral regions were considered as candidates based on the beryllium emission
intensities given in the NIST compilation of atomic emission lines 1 . Table 3-1 lists the
principal Be emission lines corresponding to the candidate spectral regions.
Table 3-1: principal Be Emission Lines Considered
Center Wavelength of
Candidate Region (nm)
313
313
332
436
436
467
467
Line Wavelength (nm)
Relative Intensity
313.0
313.1
332.1
436.07
436.10
467.33
467.34
480
320
220
300
500
700
1000
To quickly evaluate the potential of each of these spectral regions, samples were prepared
from four different materials that were felt to provide elemental compositions similar to
what would be found in a decontamination and decommissioning setting. These
materials included powdered gypsum (dry wall), iron oxide, Portland cement, and
Mancos shale. The sample of Mancos Shale was included because of the fact that this
rock unit outcrops in the general area of the Rocky Flats Site. In additio n to these
materials representing background sample compositions, a sample of pure beryllium
metal was also sparked as a means of directly evaluating the relative signal strength of
the candidate beryllium emission lines.
1
Wavelengths and Transition Probabilities for Atoms and Atomic Ions, by Joseph Reader & Charles H.
Corliss, 1980, U.S. Government Printing Office.
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Figures 3-1 through 3-4 show samp le spectra obtained with the LIBS system for each of
the four candidate spectral region.
313 nm Region
70000
60000
Intensity (arbitrary)
50000
Be Metal
Gypsum
Iron Oxide
Portland
Mancos Shale
Sparks - 1
Grating - 1200/250
Center λ - 313.04 nm
Laser Energy - 100mJ
40000
30000
20000
10000
0
300
305
310
315
320
325
Wavelength (nm)
Figure 3-1: Evaluation spectra for the 313 nm spectral region.
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332 nm Region
25000
Be Metal
Sparks - 1
Grating - 1200/250
Center λ - 332.0 nm
Laser Energy - 100mJ
Gypsum
Iron Oxide
20000
Portland
Intensity (arbitrary)
Mancos Shale
15000
10000
5000
0
320
325
330
335
340
345
Wavelength (nm)
Figure 3-2: Evaluation spectra for the 332 nm spectral region.
436 nm Region
20000
Be Metal
18000
Sparks - 1
Grating - 1200/250
Center λ - 436 nm
Laser Energy - 100mJ
Gypsum
Iron Oxide
16000
Portland
Mancos Shale
Intensity (arbitrary)
14000
12000
10000
8000
6000
4000
2000
0
420
425
430
435
440
445
450
Wavelength (nm)
Figure 3-3: Evaluation spectra for the 436 nm spectral region.
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467 nm Region
10000
Sparks - 1
Grating - 1200/250
Center λ - 467, or 457 nm
Laser Energy - 100mJ
Be Metal
9000
Gypsum
Fe-Oxide
8000
Portland
Mancos Shale
Intensity (arbitrary)
7000
6000
5000
4000
3000
2000
1000
0
445
450
455
460
465
470
475
480
Wavelength (nm)
Figure 3-4: Evaluation spectra for the 467 nm spectral region.
All of the spectra shown in figures 3-1 through 3-4 were obtained with a LIBS system
utilizing a 100 mJ/pulse laser system using only one spark. Clearly the most intense line
is the 313 nm doublet shown in figure 3-1. Note that the 313 nm emission line saturates
the detector at 65k counts with only one spark contributing to the spectrum. It is also
noteworthy that there appear to be no significant spectral interferences with the 313 nm
line, based on the 4 materials used as surrogates for ambient dust.
The 332 nm beryllium line is the next most intense line at approximately 23k counts.
Note that it also appears to be free of significant spectral interferences. The 436 nm
region, shown in figure 3-3 does exhibit a beryllium emission line, but there are
significant spectral interferences in this region. Figure 3-4 shows almost no beryllium
emission from the 467 nm line under the conditions of the LIBS spark. Also note that
there are a number of other spectral features that could cause problems with spectral
overlap.
Using these results as a general guide to the various spectral regions, actual wipe samples
from RFETS were evaluated using the same LIBS system. These LIBS analyses were
carried out with the spectrometer set to a center wavelength of 323 nm to ensure that both
the 313 nm and 332 nm emission lines would be measured. Figure 3-5 show the results
for the LIBS analysis of one of these RFETS samples, BB06 from building 444. Also
shown on the plot is a simulated spectrum that was generated using the emission data
from the NIST tables, and spectra collected from the analysis of blank mixed cellulose
ester (MCE) filter media. The spectral simulation was investigated as a means of
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predicting the prototype instrument performance under a variety of “What If?” scenarios,
where a variety of potential interfering agents were postulated to be present in the
sample. Figure 3-5 is characteristic of the various RFETS samples analyzed in that the
region around the 313 nm beryllium emission line is free from any significant spectral
interferences.
Figure 3-5. Plot of LIBS spectra from RFETS Sample BB06 & simulated spectra.
The background spectra for various candidate filter media were also evaluated to identify
any media with particular spectral features within the candidate spectral regions. In
general, none of the filter media tested exhibited any significant spectral features in any
of the four candidate spectral regions.
Based on these results, and field measurement experience using LIBS to measure
beryllium abundance in soils, a spectral region was selected that would include both the
313 nm and the 332 nm beryllium emission lines. This spectral region is centered at a
wavelength of approximately 323 nm.
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3.2 Filter Media Selection
Selection of the optimal filter medium to be used in the instrument’s CAM and Wipe
Modes involved a number of interrelated parameters, including:
•
•
•
•
Flow rate
Spectral emission characteristics
Particle retention
Durability
A number of different filter media were considered as candidates early in the method
development efforts. These included:
1. Millipore RW-19, a mixed cellulose ester (MCE) media,
2. Whatman EPM 2000, a glass fiber filter,
3. Gelman Type AE, a glass fiber filter, and
4. Whatman # 41, a MCE filter media.
The Whatman # 41 filter media was evaluated principally as a candidate for wipe
sampling, since it is commonly used in this capacity for beryllium sampling in the DOE
complex. It was not considered for use as with the monitor’s CAM mode.
Particle retention includes both the ability to capture particles from the air stream, as well
as its ability to hold onto particles during the sparking process. The process of plasma
formatio n (sparking) is markedly violent on the small scale. The shock wave generated
by the sudden plasma formation can cause the particles collected on the filter media
adjacent to the spark location to be ejected if the filter media does not hold them tightly
enough. In general, if the particles are held on the media surface, these losses will be
higher than if the particles have penetrated the media. For these reasons, and because of
their brittleness, the nucleopore type filter media were not considered as candidates for
the CAM mode of operation.
The Millipore RW-19, Whatman EPM 2000, and the Gelman Type AE were evaluated
for their flow characteristics both in an unloaded condition and loaded with dust
approximately equivalent to the nuisance dust level of 5 mg/m3 for a sampling time of 6
minutes. Both of the glass fiber filters exhibited slightly better flow characteristics than
the Millipore RW-19 in both the unloaded and loaded configuration. Both the RW-19
filter media and the glass fiber media responded well to the LIBS sparking process, with
the glass fiber media exhibiting a melt crater that penetrated approximately half of the
media thickness.
The RW-19 media incorporates a fibrous support material to provide extra strength for
the otherwise brittle MCE media. During the sparking process the MCE media is
completely removed from the filter in the area where the spark occurs. The fibrous
support is much more resistant to the thermal and mechanical stresses of the spark
(plasma) formation, and remains largely unaffected. The photos in figure 3-6 illustrate
this.
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Figure 3-6: Photos of RW-19 filter media following LIBS analysis.
Further research into the composition of the glass fiber filter media, and in particular the
available data regarding trace element composition of the glasses used, revealed that
there may be beryllium contamination in these types of filter media. Because of this, and
because the RW-19 MCE filter showed the least amount of structure in the LIBS spectra
It was selected as the optimal filter media.
3.3 Internal Standard Evaluation
The team also investigated a number of internal standard elements and configurations for
potential use in the system. There were several issues to be investigated: 1) the internal
standard needs to have an emission line(s) within the spectral window of the 313nm line
for beryllium without interfering with the Be line, 2) the internal standard must not
interfere with the ambient dust emission lines, 3) the internal standard must have an
emission that is repeatable on a spark-to-spark basis, and 4) the internal standard must be
able to be placed onto filter media by itself for normal use and with beryllium for
validation/calibration samples. Preliminary work with La, Li, and Lu, resulted in the
selection of La as the most likely candidate based upon the location of the La peaks in
relation to the beryllium peaks. More detailed analysis, however, showed that the La
peaks do have significant overlap with the ambient dust components seen in the RFETS
samples. Figure 3-6 shows some example spectra illustrating this. Spectral overlap with
components in the ambient dusts will ultimately corrupt the usefulness of the internal
standard, as the measured peak intensity for the internal standard will not be dependant
upon just the abundance of the internal standard.
In addition, it appeared that it would be exceedingly difficult to place an internal standard
onto the filters in a reproducible and predictable manner. If the internal standard were
not evenly distributed across the sample it would actually introduce additional
uncertainty into the measurement. Based on experience with introducing beryllium, from
a plasma standard solution, onto filters, it was concluded that placing both Beryllium and
an interna l standard onto the filter simultaneously with perfect spatial distribution would
be very difficult and costly. It was therefore decided to look into other methods for
introducing an “internal” standard that could be used to potentially reduce the spark-tospark variations associated with LIBS analysis.
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40000
Arbitrary Y
30000
20000
Final Report
Beryllium
Copper
RFETS BB-06
10000
Lanthanum
0
305
310
315
320
Arbitrary X
325
330
335
Figure 3-7: Example spectra for lanthanum as an internal standard.
One configuration worthy of noting is to use a metallic wire mesh underneath the filter.
In this configuration, the laser penetrates through the filter, and sparks both the filter and
the underlying metal. The metal must be in the form of a screen or mesh to allow air to
flow through the filter during air sampling in the CAM mode and during the LIBS
analysis. An attractive aspect of using a wire screen beneath the filter media is that it
could be implemented with a minimal amount of labor and cost, while retaining
confidence that the spatial distribution was known and consistent. Several sets of test
were conducted. One set of tests looked at the emissions from some common metals
screens to look for likely candidates and another set addressed whether the system could
reproducibly interrogate the filter and mesh simultaneously. If the laser emission does
not consistently cause strong emissions from the wire mesh underneath the filter, then
this configuration would be inadequate.
The results of the other tests, unfortunately, showed that the laser does not reproducibly
interrogate the mesh underneath the filter. Tests of wire meshes under RW-19 filter
media indicated that the laser did not have the power to penetrate the filter and cause
appreciable sparking of the underlying mesh. The conclusions from all of the tests on the
various approaches to incorporating an internal standard into the filter media are: 1)
finding a universal internal standard that does not have any peak overlap with Beryllium
and the ambient dust components is very difficult, 2) if such a material existed, the
requirements for applying it with the necessary spatial uniformity may be prohibitive, and
3) using a mesh screen underneath the filter is less then ideal. Thus, evaluation of the use
of an internal standard resulted in the decision to not include it in the prototype system
design.
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3.4 Sample Preparation Techniques
Development of any type of instrumentation geared towards elemental analysis involves
the preparation of suitable samples to test instrument response. In this case the element is
beryllium, and the sample matrix is filter media. As mentioned in section 3.1, a variety
of filter media were evaluated for suitability for this application. Regardless of the filter
media, the same general procedures were followed. The major difference in sample
preparation had to do with the form of the beryllium tha t was used. Two different forms
of beryllium were used: (1) a beryllium plasma standard solution, and (2) size selected
beryllium particulates.
The plasma standard was purchased commercially, and supplied with NIST traceable
documentation. There are no commercially available beryllium particulate standards
traceable to NIST or otherwise. We were fortunate to be able to make use of size
selected beryllium particulates that had been collected by Dr. Mark Hoover at one of the
Brush Wellman locations. Initially it was thought that the plasma solution standard
would only be used for the initial measurements designed to select the appropriate
spectral region(s) of interest, and in evaluation of the various candidate internal
standards. The beryllium partic ulate material would be used in all samples used to
determine the quantitative performance of the prototype monitor. As will be discussed in
the following section, this turned out not to be the case.
Many traditional analytical techniques, such as Atomic Absorption or Inductively
Coupled Plasma Emission Spectroscopy analyze a solution for the concentration of the
analyte. Correspondingly calibration standards that are themselves solutions of known
concentration are used. In contrast, LIBS analysis of beryllium particulates on filter
media is based on knowing the total mass of beryllium deposited on the filter. Moreover,
this approach requires that either the filter media be analyzed in such a way that all of the
beryllium mass is involved in the analysis interaction, or that at least a constant fraction
be involved in the analysis interaction. Variability of the mass fraction of the beryllium
on the filter that truly is involved in the LIBS interaction is a source of variability that
contributes to the overall uncertainty in a LIBS measurement. In order to ensure that the
second condition is not grossly violated, it becomes necessary to prepare the filter
samples in such a way as to present all of the beryllium mass within the filter area that
will be interrogated by the LIBS process. It is easy to see that if some beryllium mass
were either lost from the filter, or deposited on a part of the filter that would not get
sparked, the instrument response would not correlate well with the beryllium mass.
3.4.1 Solution Based Samples
The first step in developing a preparation procedure for the solution-based samples, was
to determine what solution volume would appropriately fill the filter area to be
interrogated by the LIBS process. Too little solution volume would result in beryllium
areal concentrations (µ g Be/cm2 ) that are unreasonable for the total mass deposited
compared to the real samples, especially CAM samples. On the other hand, if too large
of a solution volume were used, the solution would wick out to the edges of the filter
media and be unavailable to interact in the LIBS process. Through some trial and error it
was determined that a solution volume of 50 µL was an appropriate compromise for filter
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media to be analyzed in the 47 mm diameter filter cassettes. A solution volume of 8 µL
was found to be appropriate for the 25 mm diameter filter cassettes.
Total mass deposited on the filter media ranged from as little as 0.05 mg Be to as much
as 20 mg over the course of the Method Development effort. Working solutions that
would result in a partic ular target mass of Be on a filter when 50 µL (or 8 µL) of the
solution was deposited were made by serial dilution of either a 10,000 ppm, or a 1,000
ppm Be plasma standard. Volumetric measurements were made with either a Rainin
EDP2 adjustable electronic pipette (0-250 µL) or a Hamilton model 1708-32,
mechanically adjustable pipette (0-10 µL). A 10 ml volumetric pipette was used to
dispense dilutant in some instances. The dilutant used was a 5% HNO3 solution made
from a low metals reagent grade Nitric acid and distilled/deionized water.
To ensure that all of the beryllium in the solution would remain on the filter as it dried,
the filter media was loaded into a Canberra filter cassette with the filter support media
removed. In this way the filter cassette would hold the filter media by the edge s, but
nothing would be in contact with the filter media in the area where the solution was being
deposited. Figure 3-8 shows a series of the filter cassettes ready to be loaded with filter
media. Once the solution was deposited on the filter media, a heat lamp was used to
thoroughly dry the sample before storage in a plastic petri dish. If the samples were not
thoroughly dried prior to storage, the residual highly concentrated acid would dissolve
the filter media.
Figure 3-8: Filter cassettes, used to support the filters during sample preparation
3.4.2 Particulate Based Samples
In contrast to the preparation of the solution samples, preparation of the particulate
samples started with making a particle suspension master. As mentioned previously, the
size selected beryllium particles were donated by Dr. Mark Hoover, currently at NIOSH
in Morgantown, WV. Dr. Hoover used I-400 material provided by Brush Wellman. The
power was placed in a reservoir and aerosolized using a dry powder blower (Model 175,
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DeVilbis, Inc., Somerset, PA). The beryllium particulates were collected in aerodynamic
size fractions using a Southern Research Institute 5-stage aerosol cyclone (SM79)
operated at 24 actual liter per minute flow rate. A concentric electrostatic precipitator
(ESP, Model02-1700, Mine Safety Appliances, Inc., Pittsburgh, PA) was used as the
backup collector. The cyclone stages and corresponding aerodynamic size range are
given in Table 3-2 below. Following collection the size selected material was stored in
metal tins.
Table 3-2: Cyclone stage and corresponding aerodynamic size range of the
particulate beryllium
Cyclone Stage
1
2
3
4
5
ESP (Backup)
Aerodynamic Size Range (µm)
> 5.9
2.5 – 5.9
1.5 – 2.5
0.74 – 1.5
0.5 – 0.74
≤ 0.5
Master particle suspensions of various beryllium concentrations (µg/ml) were prepared
from the size-selected material described above. These master suspensions were
prepared by massing a target amount of beryllium into a 25 ml glass scintillation vial
using a 5-digit analytical balance. A known volume of reagent grade ethanol (typically
10.0 ml.) was added as the suspension carrier fluid using a volumetric pipette. The vial
was immediately capped.
Working suspensions were prepared from these master suspensions by serial dilution.
Prior to any extraction from the master suspensions, or the working suspensions, the
tightly capped vial was shaken vigorously and then placed in an ultrasonic bath for a
minimum of 5 minutes. The cap was removed with the vial still in the ultrasonic bath,
and a pipette (see above) was used to extract the required volume of the suspension. The
vial was capped immediately following extraction of the suspension aliquot. Care was
taken to keep the bath water temperature near room temperature. This minimized errors
in the volumetric measurements, and keeps evaporative losses of the ethanol carrier fluid
to a minimum.
The same considerations with regard to areal deposition and volume of suspension
deposited that applied to the solution samples described in section 3.3.2, apply equally to
the particulate samples discussed here. Figure 3-9 shows three samples prepared from
beryllium particula te suspensions. The total beryllium mass on each filters is 1.0 µg.
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Figure 3-9: Filters prepared using the 2.5 – 5.9 µm beryllium particulate suspension
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4 SYSTEM DESIGN
4.1
Hardware Design
4.1.1 Design Approach
One of the design aspects that would have a very impact on the design approach was the
sampling approach used to acquire the air sample for LIBS interrogation. In order for a
LIBS instrument to function as a continuous air monitor for beryllium, a suitable air
sample must be obtained and presented for interrogation by the LIBS process. There are
essentially two ways that this can be accomplished. The first approach is to draw a
stream of air past a sampling location where the laser spark is focused into the air stream.
When the spark forms in the air stream, any particulates, including the ambient dust and
beryllium, that are within the spark volume will be exposed to the high temperature
plasma of the spark, and produce an optical emission signal. The second approach makes
use of conventional filter-based air sampling techniques, where a known volume of air is
drawn through a suitable filter media. The analyte of interest, in this case beryllium, is
trapped on the filter and therefore made available for LIBS interrogation.
Directly sparking an air stream is technically simpler, but it also imposes some significant
limitations on the instrument performance. While it offers an immediate response to the
presence of a large abundance of beryllium in the air stream, this fast response time
comes at the expense of instrument sensitivity. Conversely, the overall sens itivity, and
therefore minimum detection limit, offered by sampling on filter media may be as much
as 2 to 3 orders of magnitude better than directly sparking the air stream for a given LIBS
hardware configuration. This difference in sensitivity is determined in large part by the
signal to noise ratio for an individual spark. Directly sparking the air stream results in
much poorer sensitivity because the actual volume of sample air analyzed by the direct
spark method is equivalent to the spark volume itself. In the case of a filter-based
method, the volume of sample air analyzed is given by dividing the total volume of air
sampled by the number of sparks required to completely interrogate the filter area. The
higher volume of sample air represented on the filter means a larger mass of beryllium on
a spark by spark basis, equating to a larger signal to noise ratio.
Another significant benefit of the filter based sampling approach is the ability to easily
include spike and blank samples in the analysis routine. In the proposed instrument
system blanks are easily obtained by simply bypassing the air-sampling step, and
analyzing an unused filter. Spike samples may be prepared using laboratory methods of
loading beryllium particulates onto the same filter media as is used for the air sampling.
This ability to analyze spike and blank samples during the normal air sampling routine
greatly enhances the reliability and defensibility of the data generated with the airsampling instrument. Because of these adva ntages, SEA selected the conventional air
sampling on a filter media for this instrument.
Having settled on a filter media based sampling approach, one of the major design
aspects of the monitor was what type of filter holder (filter cassette) should be used?
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Again two fundamentally different options were apparent. The first option considered
was the use of a reusable filter cassette. In this scenario a relatively expensive, metal
filter cassette could be purpose designed for the automated handling equipment that
would be needed to move individual filter cassettes to the various functional stations
within the monitor. These filter cassettes would necessarily need to be cleaned in
between uses to ensure that there was an acceptably low probability of beryllium cross
contamination between successive uses of these filter cassettes. The necessity to clean
the filter cassettes would also require that more than one set of filter cassettes be
available so that recently used filter cassettes could be cleaned, while the monitor was
still in use with a second, or probably third set of filter cassettes. After an initial
consideration, it became apparent that the overwhelming cost aspect would be the labor
associated with cleaning the filter cassettes. This labor cost could easily approach the
baseline costs for laboratory analysis of beryllium filters reported by RFETS at
$22/sample.
The alternative to reusable filter cassettes is disposable filter cassettes. In this case a
relatively inexpensive and disposable filter cassette is used for only a single use, then
discarded as a waste. The key to this approach is the design of a filter holder that can be
manufactured relatively cheaply in modest numbers. It also must have the necessary
sophistication of design so that each filter cassette behaves the same, i.e. there is not a
significant variation in overall collection efficiency nor particulate distribution over the
filter area from one filter cassette to the next.
To keep manufacturing costs acceptable, such a filter cassette would likely be fabricated
as an injection molded part, or parts. Design of such a filter cassette is a relatively
straightforward process. The initial production set-up costs, however, can be very high.
These costs include not only the design work for the particular filter cassette, but the
costs of fabricating the master injection molds, and production set-up costs as well.
Initially this approach appeared to be beyond what the project budget could handle.
Fortunately, such a filter cassette was already commercially available from Canberra
Industries. This filter cassette, pictured in figure 4-1, is also available in two sizes, a 47
mm size, and a 25 mm size. And while the design of the filter cassette was not
specifically tailored for automated handling, it was amenable to automated handling. The
commercial availability of these filter cassettes made this the clear choice.
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Figure 4-1: The Canberra filter cassettes utilized in the prototype monitor design
Another very important aspect of the overall design approach is that of contamination
control. The beryllium monitor will largely be used in areas controlled for radiological,
as well as beryllium contamination. Consequently, the monitor design must address
control of contamination. This includes not only protection of the instrumentation from
external sources of contamination, but also protecting the environment surrounding the
instrument, and in particular the operators, from possible sources of contamination within
the instrument itself.
Keeping external sources of contamination out of the monitor internals is necessary
because of the need to service various components over the life of the monitor, and a
desire to be able to use the monitor in both contaminated and clean areas. Control of
external sources of contamination is traditionally accomplished by incorporating an
instrument ventilation scheme that keeps the instrument enclosure positively pressurized
with clean or filtered air. Any openings in the monitor enclosure will leak clean air out,
and not allow contaminated air to enter. Thus the monitor internals are protected from
contamination, and only the monitor exterior need be considered when decontamination
must be carried out. The instrument configuration also incorporates smooth external
surfaces that are easily washed down, and minimizes nooks and crannies that can
accumulate contaminants. These design features make external decontamination easily
accomplished.
Because the monitor handles not only samples representing the ambient air, but also wipe
samples containing unknown amounts of beryllium, and spike, where the filter media is
purposely doped with beryllium, there was concern about the potential for release of
beryllium from the instrument interior. The traditional means of controlling potential
sources of contamination from within an instrument, or a part of an instrument is to
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utilize a ventilation system that depressurizes the area of concern and filters the exhaust
from this system.
Since it is not possible to have it both ways, the monitor enclosure can not be
simultaneously pressurized and depressurized, some form of compromise needed to be
worked out. The following approach was developed for this instrument design.
•
•
•
•
Segregate – Segregate those components that necessarily must be in intimate
contact with beryllium- laden samples from those that do not.
Pressurize – Employ a ventilation system that will keep the entire monitor
enclosure positively pressurized with respect to the ambient atmosphere with
HEPA filtered air.
Depressurize Locally – Employ a negative pressure ventilation system within the
monitor enclosure that targets the most likely sources of fugitive beryllium
contamination from the monitor internals.
Seal - Seal all of the openings in the enclosure envelope that can be sealed.
The result of applying the segregation concept was to split the monitor enclosure into two
compartments, a CAM/Wipe module where the filter cassettes would be handled and
analyzed, and an instrumentation module where all remaining components would reside.
Both modules would be positively pressurized by a HEPA filtered ventilation system.
Since the most likely source for fugitive beryllium contamination from within the
monitor is the process of analyzing the filter media by the LIBS process, a separate
negative pressure ventilation system was developed control potential emissions from this
source. This vent system would be completely contained within the monitor enclosure,
and therefore within the positive pressure environment. The final design element is
sealing all penetrations in the monitor enclosure envelope. The traditional leaky points in
an instrument enclosure are panel seams, and fastener holes, and switch and cable
penetrations. The approach adopted was to first, minimize the number of penetrations of
the enclosure design, and second, seal all of those penetrations that were absolutely
necessary. This would include sealing washers on all of the fasteners, and gaskets and
other seals on all of the cable and connector penetrations and monitor panels. The result
of applying this design philosophy is described in section 4.1.3.
4.1.2 Design Trade Space
The evolution of any system from the design concept through fabrication of a working
prototype necessarily involves numerous trade-offs between competing objectives. This
is generally referred to as operating in the design trade space. It is in the design trade
space that the lofty goals and objectives are reduced to practical design elements by the
realitie s of cost, schedule, and physics. Evolution of the prototype beryllium monitor was
no different, in this respect, than many other DOE sponsored research and development
effort. This section attempts to address the major trades made during development of the
monitor. It is by no means an exhaustive treatment of the trades made between various
design aspects of the system.
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4.1.2.1 Direct Surface Monitoring Capability
As discussed in section 2.2, the capability to directly interrogate surfaces was determined
to represent a significant compromise in the overall design of the monitor, with little
return in terms of added capability. With the consent of the various project technical
monitors, and the end users, it was decided to defer development of this capability until
the basic monitor performance and utility could be evaluated. The rational for this
decision is presented in Section 2.2, and will not be repeated here.
4.1.2.2 Sample Handling System
The original concept for the sample handling system called for implementation of a
reusable filter cassette to hold the filter media for both the wipe and CAM operational
modes. It also called for purpose designed filter cassette handling sub-systems. These
were to be a number of linear actuators coupled with an overall compone nt placement
that would allow single axis motion to be used to transfer cassettes between the various
stations (filter storage, air sampling, LIBS analysis, and disposal).
Commercially available cassettes would be modified to incorporate a kinematic mount,
which would provide the necessary registration and position accuracy for the samples
with respect to the laser beam. SEA has used kinematic mounts to hold samples in the
correct position with respect to the laser beam in other LIBS systems, and was confident
in the utility of such an approach. It was also assumed that the same size filter media
would be used for both the wipe and CAM operational modes. The intent was to employ
a relatively small number of filter holder sets used with each monitor (one set would
equal the full capacity of the monitor). These filter cassettes would be cleaned between
uses, in the same way that glassware is cleaned between uses in a traditional analytical
chemistry laboratory. The labor costs of this approach are, howeve r, substantial. And
there is always the concern that the cleaning may be incomplete, resulting in false
positive results. Because of these concerns, as well as learning of the availability of a
disposable filter cassette from Canberra Industries, it was decided that a disposable filter
cassette would be used. This filter cassette is produced in two varieties, a 25 mm version,
and a 47 mm version. Additionally, the Canberra filter cassette exhibited excellent flow
characteristics, both in terms of flow rate and uniform distribution of particle loading on
the filter media, both of concern in the overall performance of the monitor. Thus, the
advantages of a disposable filter cassette outweighed the advantages of the reusable,
kinematic filter cassette, and the disposable filter cassette was selected. This decision
did, in fact, have a substantial impact on the course of monitor development.
The storage of filter cassettes in the monitor prior to sample acquisition in the CAM
mode, and prior to LIBS analys is in the wipe analysis mode, became more difficult. The
kinematic mount system to be employed on the reusable filter cassettes, was to also have
served to hold the filter cassettes into the filter magazine. Since the Canberra filter
cassettes did not incorporate a kinematic mount, sample positioning and registration
would need to rely on physical positioning of the cassette into a purposed designed
receptacle for all of the various filter cassette positions within the monitor, i.e. filter
magazines, the air sampling station, and the LIBS analysis station. The design of the
filter cassette, see figure 4-1, provided a tapered lip that was used to register the cassette
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Science & Engineering Associates, Inc.
Final Report
into the proper position in its original application, a radiation CAM. Using this means of
registering the cassette necessarily involved two axes of motion for a given placement
and retrieval stem. This drove the sample handling system design to a true pick and place
approach. Since there was certainly not the schedule or budget to develop such a system
solely for the beryllium monitor, the only alternative was to find a commercially
available system that would meet the pick and place requirements. Not surprisingly, a
robotic arm was found to be the logical choice. The objectives in selecting a robotic arm
were to meet the payload, and positioning accuracy requirements, while keeping the
overall package size and weight to a minimum. Cost was also a major consideration, in
that the original project budget did not include a robotic arm and controller. A robotic
arm was identified that would meet the general requirements. A 6-axis robotic arm was
selected over a marginally cheaper 5-axis arm to allow the overall enclosure size of the
monitor to be as small as possible. The 6-axis arm can use space more efficiently that a
5-axis arm of comparable size. In the final design, the dimensions of the CAM/Wipe
Module are determined to a large extent by the reach capabilities and maneuvering space
requirements of the arm selected. A less flexible arm could have resulted in an even
larger enclosure size for the monitor than was achieved. It should also be noted that the
placement of the various stations within the CAM/Wipe Module enclosure was
determined to an appreciable extent by the reach capabilities of the arm. As an example
of this, it was desirable to locate the air sampling inlet at a higher elevation within the
CAM/Wipe Module, but the existing location was at the vertical reach limit of the arm.
Another impact of the robot arm selection related to design trades in the area of the
system control computer and sample positioning under the fixed laser beam. The original
design concept called for the use of a set of X-Y stages to move the filter cassette in a
sparking pattern under the fixed laser beam for the LIBS analysis. The X-Y controller
would require serial communications with the system controller, and would also
contribute substantially to the overall system heat load. With the addition of the robotic
arm into the trade space, it was necessary to look seriously at using the robot arm instead
of the X-Y stages and controller. The positioning accuracy specifications and load
handling limit for the robot indicated that it could easily provide the necessary sample
positioning. Additiona lly, inclusion of the robot arm had taken one of the serial com
ports originally reserved for the X-Y stage controller. If both the robot arm and the X-Y
stage controller were implemented in the design, it would either be necessary to give up
serial communications with one of the other devices where serial communications had
been planned, or plan on using a serial expansion board to allow more than four serial
ports to be services by the operating system. Previous experience with expansion serial
hardware and the supporting driver software led the design team to reject this option as
having a high probability software problems, and result in a lower than required
reliability of operation.
The other devices that were allocated serial communication lines included the
spectrometer, the laser, and the flow meter. The flow meter has output capabilities that
include serial output of the flow data as well as an analog output line, so it would have
been possible to give up the serial communication with the flow meter and switch to an
analog signal out, in order to provide the necessary serial communications with the X-Y
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Science & Engineering Associates, Inc.
Final Report
controller. The cost of doing this would necessarily be an impact on the accuracy of the
flow measurements. This impact results from two principal sources. First, because this
path would require that the digital data in the processor of the flow meter would undergo
an digital to analog conversion in the flow meter, and a subsequent analog to digital
conversion in the multi I/O boards to be used on the computer. Both of these conversion
processes are subject to electronic noise and temperature driven errors. Secondly, the
processor capabilities of the air flow meter allow the unit to be triggered on a rising edge
flow rate signal and a on a falling edge flow rate signal. Since the air-flow volume has a
direct impact on the measurement result, it was felt that this would ultimately result in a
poor trade. The decision was made to use the robot for the required X-Y positioning of
the sample under the laser beam, and continue to use serial communications
4.1.2.3 Contamination Control
During a conference call early in the design phase between SEA, NETL and RFETS
personnel, an issue arose concerning the possibility of beryllium becoming entrained
within the exhaust of the Beryllium monitor, thus increasing the safety hazard to the user.
It was determined that the most likely scenario for release of beryllium would be from a
wipe sample and that this would occur if a filter cassette were dropped by the robot
during transport from one station to another. A semi-quantitative test was conceived and
executed to assess the potential for release of beryllium from wipe samples being
processed in the prototype instrument. To simulate this event, a series of wipe filters were
loaded with a fluorescent paint, then dropped from a height of 15” onto a hard metal
surface. The surface was examined visually, with the aid of a UV lamp, for evidence of
paint dislodged from the filter media. Additionally the filter media was weighed both
before and after the drop test to estimate the mass lost during the drop.
To estimate the mass loading of a typical wipe sample, four wipe samples were obtained
using 47 mm Whatman 41 filter media, with a wipe area of 100 cm2 . The wipes were
performed on some large diameter ductwork in SEA’s Technology Center that had not
been cleaned for a number of years. The filter media were massed before and after the
wipe sampling to determine the mass of dust collected on the filter. The average mass
increase of the four wipes was 8.4 milligrams. This mass was used as the target mass in
the preparation of the test filter media loaded with fluorescent paint.
The test procedure consisted of loading the filter with a known mass of fluorescent paint
powder, placing the filter in a filter cassette, and dropping it face down onto a hard metal
surface. After dropping, all of the filters ended up “face down” on the metal surface.
The filters were turned over in order to allow better inspection of the surface and debris.
Using a UV lamp to illuminate the area, debris showed up clearly on the black metal
surface. Photos of the filter and debris were taken using a digital camera. Finally, the
filter was carefully removed from the filter holder and a post drop mass determined.
Table 4-1 lists the mass changes for the test.
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Final Report
Table 4-1: Mass Change Results for drop tests
Sample ID
Whatman-41 A
Whatman-41 B
Whatman-41 C
Whatman-41 D
Whatman-41 E
Whatman-41 F
Amount of powder
on filter
(mg)
14.43
6.20
7.85
9.38
8.23
9.79
Amount of powder
ejected
(mg)
8.39
2.56
2.25
3.39
3.46
4.39
% of powder
ejected
58%
41%
29%
36%
42%
45%
The following photos show a “loaded” filter before and after the drop test. These photos
were taken using a UV lamp for illumination. Note the paint ejected from the filter
media on the edge of the filter cassette as well as to the upper left of the cassette.
Figure 4-2: Whatman-41A sample before (left) & after (right) drop test.
Both the visual examination and the measurement of mass indicate that a measurable
amount of the sample collected on a wipe will be ejected from the filter media if the filter
cassette is dropped within the instrument. The measurements made during this test
estimate that approximately 42 % of the mass collected on the filter media may be ejected
during a drop. Using an estimate of 60 micrograms of Be as the maximum Be
contamination typically seen on RFETS wipe samples, this would result in the loss of
approximately 25 micrograms of Be from the wipe media. As a result of these tests, it
was concluded that the exhaust from that part of the instrument that houses the filter
cassettes would require HEPA filtration.
4.1.2.4 System Cooling
Once all of the components and subassemblies were identified and located within the
integrated design, a heat budget model was developed to determine the airflow
requirements for forced air convective cooling of the instrument. The underlying
principle of the design at this point in the design process was the desire to easily clean the
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Science & Engineering Associates, Inc.
Final Report
unit so that it could be transported in and out of the various contamination zones. To this
end the design included features such as, smooth surfaces and one-piece construction.
External cooling fans and heat exchange radiators were not included due to the difficulty
in cleaning for the end-user.
The analysis of heat loading was separated into three subsets to account for the fact that
various groups of components can tolerate different temperature rises, and can be located
within different subsections of the instrument package. This segregation allows the total
ventilation requirements to be optimized. From this analysis it was determined that the
ventilation cooling system must remove approximately 1700 W of waste heat. This heat
load, and the corresponding allowed temperature rise of several key components, results
in a ventilation requirement of approximately 250 CFM. The design can accommodate
this airflow, but when it was considered that this unit might be used in small rooms, an
evaluation of the effect on ambient aerosol concentrations was needed. Operation of the
beryllium monitor with this ventilation airflow rate would act as an air cleaner due to the
HEPA filtration. For an assumed room size of 4,000 cubic feet with an air change rate of
6 volumes per hour, the beryllium monitor operating with a ventilation flow rate of 250
CFM will reduce the steady state concentration of an airborne contaminant by as much as
38%. This was deemed to be an unacceptably large impact on the measured parameter.
Correspondingly, the design team sought alternative methods of cooling the internal
instrument components.
The options considered included:
• Incorporate design elements to remove the heat via direct conduction into the
enclosure and radiative transfer to the surrounding environment.
• Remove some of the high heat generators to the outside of the filtered enclosure
• Provide the unit with an external source of chilled air for cooling
The latter scenario appeared the most attractive in the final evaluation. This option was
initially discarded due to the need to have a separate chiller/refrigeration unit that would
be very difficult for the user to decontaminate if they wanted to remove the unit from a
contamination zone. After discussing this aspect of the design with RFETS D&D
personnel, it is apparent that using a small chiller that potentially could not be cleaned
would not be considered a major problem. Operationally a cooling unit could be
designated for use in contaminated areas only and a separate cooling unit reserved for use
in non-contaminated areas. Thus the final design incorporated a separate chiller unit and
internal heat exchanger system to provide the necessary cooling for the monitor.
4.1.2.5 Spark Chamber Ventilation
Developing the design for ventilation of the spark chamber also involved a number of
trades between competing objectives. In the very early conceptual designs it was
considered necessary to provide ventilation of the spark chamber due to the nature of the
LIBS process. Dur ing formation of the plasma volume, and its subsequent collapse,
some sample material and filter media is ejected from the filter surface. If there is no
means to remove this material it will quickly accumulate to levels that will result in cross
contamination from one sample to another. Ventilation of the spark chamber was also
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necessary to keep this ejected material off of the optics, thereby protecting them from
absorption of the infrared laser emissions and the resulting thermal damage. Ventilation
of the spark chamber was also to be used as a means of controlling potential releases of
beryllium from the instrument. If the spark chamber ventilation system keeps the spark
chamber at a negative pressure relative to the rest of the instrument enclosure, any leaks
in the spark chamber will only allow air and potential contaminants to enter the chamber.
A concept that was introduced into the design process in its very early stages was that of
drawing some of the ventilation air through the filter during the LIBS analysis process.
The idea behind this concept was to recover some of the analyte (beryllium) that was
being lost from the filter from this ejection process back into the analysis, thereby
potentially increasing the monitor’s sensitivity.
One unintended consequence of the combination of operating the spark chamber at a
negative pressure and incorporating air flow through the filter cassette during the LIBS
analysis was a puffing of the filter media in the filter cassette during its placement into,
and most commonly during its retrieval from the spark chamber. The puffing of the filter
media occurred when the filter cassette was disengaged from nipple supplying the
negative pressure airflow to the filter cassette. This momentarily allowed the ambient
pressure outside of the spark chamber to tend to flow through the aperture in the bottom
of the filter cassette, through the filter media and into the spark chamber. The driving
force for this flow component is remove when the seal between the top surface of the
filter cassette and the bottom of the spark chamber is broken as the cassette is removed by
the robot arm. Developing the final ventilation design for the spark chamber involved a
careful balancing of the spark chamber negative pressure with the spark chamber
ventilation total flow rate, and selection of the appropriate filter media. In this case it
meant elimination of the use of Whatman # 41 for wipe samples, as this filter media
exhibited a much stronger tendency to puff than did the Millipore RW-19 media.
4.1.2.6 Other Design Issues
During the development of the data analysis techniques an unusual characteristic of the
LIBS spectra from the prototype monitor became evident. When one looks at the
baseline signal level as a function of spark number (by tracking the signal level over a
very narrow wavelength range in the LIBS spectra) the signal is seen to oscillate in a
periodic fashion. Figure 4-3 shows this feature of the spectral data. Recall that the
sample is being moved in a circular motion under a fixed laser beam. For a full test of
the largest diameter filter, 28 circular orbits are used. A considerable amount of effort
was expended to in an attempt to identify the source of the oscillations in the baseline,
and eliminate it. The CCD camera system, robotic manipulator, timing system, laser,
sample position, airflow and the alignment of the launch and reception optics were all
investigated as sources of the oscillations.
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Final Report
Figure 4-3: Oscillations in the spectral baseline showing a correlation with orbit.
As might be expected, the team attempted to evaluate each of the parameters individually
to isolate the cause of the fluctuations. All of the parameters, however, do effect each
other so, an attempt was made to minimize the fluctuations to the extent practical and
take this opportunity in the design/fabrication process to improve the overall system
performance whether it related to the fluctuations or not. For example:
Airflow – the airflow across and through the sample removes dust ejected during the
sparking. The ejected material can cause the light to be scattered/absorbed and the
detected signal level is reduced. The possibility that the airflow was being altering as a
function of sample position, thus causing a signal fluctuation was investigated. In
general, it was concluded that this was not the case, but in the process of investigating
this, the sample chamber design was altered to improve the airflow across the sample.
Robot/Laser Interference - The possibility that there was electronic interference between
the robot and the laser was investigated. It was concluded that this was not a factor
contributing to the oscillations.
Sample distance – the location of the sample (distance from the focusing lens) will affect
the spark/sample dynamics and the collection of the spark light. In general, the
fluctuation effect was evident at different sample positions. It was determined that the
current spacing of the sample and the focusing lens did not produce the most consistent
spark. As a result of this the sample-to- lens distance was changes. The sample was
moved closer to the laser resulting in an improved spark consistency, but did not
eliminate the oscillations.
System timing – There are a number of system triggers that, if wrong, could contribute to
the observer oscillation effect. For example, if the timing of the Q-switch trigger to the
laser were not consistent, then the laser power would fluctuate. Errors in the triggering of
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Final Report
the detector in relation to the spark would also cause fluctuation in the detected signal. In
the end, all of the timing was found to be correct.
Collection optics – The position of the optical fiber in relation to the collection lens in
front of it was re-evaluated. When the fiber is moved, the area on the filter that light is
collected from is altered. In this testing, a dramatic change in the fluctuation was not
observed. A change in the relative amount of continuum emission relative to atomic
emission was observed. The continuum (which is considered noise) could be reduced
considerably by a better positioning of the fiber. In addition, this testing prompted a
more rigorous evaluation of how much of the spark was being collected. The spark is
typically 5-7 mm in diameter and it was determined that the collection optics where only
viewing a 2-3 mm diameter circle at the center of the spark. In general, it was felt that
this “subsampling” of the spark may have contributed to signal fluctuations, so the last
optical element in front of the fiber was changed. The new element results in the
collection spot to be about the same size of the spark, i.e. about 7mm in diameter.
Stray light – As the sample chamber is being moved under the laser, it was postulated
that stray light reflecting off the sample chamber walls could be causing the fluctuations.
After several tests with darkening the chambers and removing elements of the
surrounding hardware, it was determined that this was not the cause.
Sample tilt – the most dramatic effect on the fluctuations that could be identified was
sample tilt. In order to evaluate this, a large tilt in the sample artificially created and the
resulting spectra evaluated for oscillations. This produced signal fluctuations much like
had been observed. As a result, a number of elements of the sample support structure
were re-evaluated and some modified to minimize the tilt of the sample. The exact tilt of
the sample was measured and this fluctuation effect is evident even with a 0.005” tilt in
the sample. It would be very difficult to design system that did better then 0.005” tilt, so
several key parameters were improved to insure that the sample is kept as flat as possible.
Data Analysis – The ability of correcting for this effect within the data analysis step was
investigated. It appears that relatively simple manipulation of the data can be performed
that will result in a “correction’ of the spectra for the systematic oscillations in the signal.
During the investigation to understand and correct the signal fluctuations, a better
understanding how many of the system parameters relate to each other and how each
effects the signal quality was developed. The eventual conclusion that was reached was
that sample tilt is most likely the dominant factor in the signal fluctuations and that the
current system design minimizes sample tilt without resorting to extreme measures.
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Final Report
4.1.3 Final Design Configuration
4.1.3.1 Monitor Overview
The general approach used to design the monitor was to use a robot arm to move
individua l filter cassettes from one station within the monitor to another to accomplish
the necessary functions of both CAM operation and analysis of wipe samples. The
following steps summarize the basic cycle of the wipe analysis function:
1. Obtain the next filter cassette in the analysis sequence from the Filter Carousel,
and place it in the Spark Chamber in the LIBS Column.
2. Conduct the LIBS analysis of the sample.
3. Retrieve the filter cassette from the Spark Chamber and dispose of the filter
cassette into the Spent Filter Receptacle.
The CAM function requires the addition of several steps to accommodate acquisition of
an air sample. The basic cycle for the CAM function is as follows:
1. Obtain first unused filter cassette from the Filter Carousel, and place it in the Air
Sampling Station.
2. Acquire the air sample on the first filter for an operator specified period of time
(~15 min).
3. Retrieve the first filter cassette from the Air Sampling Station and place it in the
Spark Chamber in the LIBS Column.
4. Retrieve the second filter cassette from the Filter Carousel, and place it in the Air
Sampling Station.
5. Start acquisition of the second air sample.
6. Conduct the LIBS analysis of the first sample.
7. Retrieve the first filter cassette from the Spark Chamber and dispose of the filter
cassette into the Spent Filter Receptacle.
8. Retrieve the second filter cassette from the Air Sampling Station and place it in
the Spark Chamber in the LIBS column.
9. Retrieve the third filter cassette from the Filter Carousel and place it in the Air
Sampling Station.
10. Start acquisition of the third air sample.
11. Conduct LIBS analysis of the second filter cassette.
12. Retrieve the second filter cassette from the Spark Chamber and dispose of it in the
Spent Filter Receptacle.
13. …
This sequencing continues for the scheduled number of cycles, which is the total time
scheduled for the CAM run divided by the air sampling time selected for the CAM run.
Note that the system is multi-tasking in that it is conducting the LIBS analysis while an
air sample is being acquired. The time required to complete a LIBS analysis of a CAM
sample (a 25 mm diameter filter cassette) is approximately 2 minutes, significantly
shorter than the suggested pump time for air sampling. This means that the system can
include analysis of a spike or a blank into the analysis sequence between two CAM
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Final Report
samples without interrupting the air sampling coverage for pump times down to
approximately 6 minutes. The system requires approximately 40 seconds to complete all
of the robot moves necessary to retrieve a CAM sample from the Air Sampling Station,
move it to the Spark Chamber, retrieve the next filter cassette from the Filter Carousel,
place it in the Air Sampling Station, and start the pump for the second sample. That is to
say that the pump is only off for 40 seconds between successive air samples.
The Filter Carousel capacity, 50 unknowns, 5 Spikes and 5 Blanks, is sufficient to allow
the monitor to be run for over 5 hours with the pump time as low as six minutes, and over
13 hours at the recommended pump time of 15 minutes. The 15-minute recommended
pump time arises from the LIBS analysis performance in combination with the pump
flow rate that can be achieved.
It should be noted that the robot is the only active motion control system utilized in the
system design. The robot is responsible not only for moving filter cassettes from stationto-station, but also for moving the filter cassette under a fixed laser beam during the LIBS
analysis. This is accomplished by mounting the Spark Chamber, the enclosure where the
LIBS analysis takes place, on a pair of X-Y translation stages and providing a point on
the Spark Chamber for the robot hand to grip it. The robot arm then moves the Spark
Chamber in a series of concentric circles of increasing diameter while the laser is fired at
a repetition rate of 15 Hz. This LIBS interrogation starts at the center of the filter and
moves out to the filter edges.
Figure 4-4 shows the SPARK I.D.™ Beryllium monitor configuration. Note that the
main part of the monitor system is segregated into two different modules. The
CAM/Wipe Module contains those components that must be in contact with the filter
cassettes, and therefore exposed to potential beryllium contamination.
The
Instrumentation Module contains the bulk of the remaining components in an enclosure
that is protected from exposure to potential beryllium contamination. There are
essentially two components that are external to the monitor enclosure system. These are
the chiller, and a rotary vane pump for air sampling.
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Science & Engineering Associates, Inc.
In-Line
HEPA
Filter
TSI
Flowmeter
MB840-B
Cent. Blower
& HEPA Filter
Spark Chamber
In-Line
HEPA Filter
Spark Chamber
In-Line
Pre-Filter
Robot Arm &
Hand Set
Filter Carousel
Mitsubishi
Robot
Controller
SX Chip
Timing
Controller
PC104
SB Computer System
Relay & I/O Boards
Gast
0523-101Q
Air Sampling
Pump
SX Q-Switch
Driver
Spent Filter
Receptacle
CAM / Wipe Module
Air
Sampling
Station
Spark Chamber
Ventilation
Blower
LIBS Column
Optics
Spark
Chamber &
X-Y Stages Assembly
In-Line
HEPA
Filter
Passive Flow
HEPA Filter
Andor
Chromex 1/4 M
DB420-OE
CCD Detector Spectrometer
Ocean Optics
HG-1
Cal Source
Big Sky
CFR 200
Laser Head
Big Sky Laser
Mini- Ice
Power Supply
Liquid-To-Air
Heat
Exchangers
Instrumentation Module
Ambient
Air Temp.
RTD
Final Report
Affinity
2 kW Chiller
Electronic
Fiber Optic
IR Laser
Air
Cooling Fluid
Figure 4-4: Simplified block diagram of the SPARK I.D.™ Beryllium Monitor.
A general description of the function of each of the primary units labeled is given below.
PC104 SB Computer – The PC104 single board computer and associated relay and I/O
boards serve as the primary system controller. They are mounted within the
Instrumentation Module. This computer includes a hard disk, also mounted within the
Instrumentation Module, and a flat panel LCD display and membrane keyboard/mouse
that are mounted on the front of the monitor enclosure. Using the custom application
software written for this monitor, the PC104 computer controls almost all of the activities
that are required for the hardware to operate as a beryllium continuous air monitor and
wipe analyzer. Some time critical timing functions are provided by a dedicated
microprocessor, the SX Chip Timing Controller.
SX Chip Timing Controller – The SX chip timing controller provides the timing required
to coordinate the laser firing with the CCD detector acquisition and robot movement of
the Spark Chamber to achieve LIBS interrogation of the entire filter sample. The SX
Chip Timing controller is mounted in the Instrumentation Module. Firing of the laser is
achieved by sending the laser controller a pulse to trigger the flash lamp at a repetition
Contract DE-AC26-00NT40768
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Science & Engineering Associates, Inc.
Final Report
cycle of 15 Hz, and supplying the laser head with a pulse to trigger the Q-Switch at an
appropriate delay time following the flash lamp pulse. Because of the need to isolate the
SX controller from the intense RF noise resulting from the Q-Switch circuitry in the laser
head, the SX circuit uses a fiber optic to provide optoisolation between the SX Chip
circuit and the SX Q-Switch Driver. It is the SX Q-Switch Driver that actually produces
the electrical pulse to trigger the Q-Switch.
SX Q-Switch Driver – The SX Q-Switch driver provides the driver circuitry to accept the
optical pulse from the SX Chip Timing Controller and produces the electrical pulse that
actually fires the laser Q-Switch. The SX Q-Switch Driver is mounted in the CAM/Wipe
Module.
Big Sky Laser Mini-Ice Power Supply – The Mini-ICE unit is the power supply and
cooling unit for the laser head. It is mounted in the Instrumentation Module. Under
normal operating conditions, i.e. when the system is being controlled by the Be CAM
software, all of the Mini-Ice functions are set and controlled by either the PC104
Computer or the SX Chip Timing Controller. At certain times during some maintenance
procedures it is necessary to operate the laser manually. For these instances a remote
hand controller may be connected to the Mini-Ice for the purposes of operating the laser
system.
Big Sky CFR 200 Laser Head – The laser head is the source of laser energy and is
mounted on the LIBS column in the CAM/Wipe Module. It is aligned with the optics
assembly and the sample aperture in the bottom of the Spark Chamber.
Optics Assembly – This system of optics and mounts accepts the laser light, focuses the
laser onto the sample, collects the plasma emission, and launches the emission into an
optical fiber bundle that is connected to the input of the spectrometer. It is mounted on
the LIBS column within the CAM/Wipe Module.
Spark Chamber & X-Y Stages – The Spark Chamber is the enclosed and ventilated space
in which the LIBS plasma, or spark, is produced on the filter surface. An aperture in the
bottom of the Spark Chamber allows a filter cassette containing the filter sample to be
introduced into the correct position with respect to the focused laser beam and the
emission collection optics. The Spark Chamber is mounted on a pair of orthogonally
arranged stages that allow the robot arm to move the entire Spark Chamber in a series of
orbits of increasing diameter. This is the bottom most part of the LIBS column.
Chromex ¼ m Spectrometer & Andor CCD Detector – The emission from the spark is
collected by the Optics Assembly and launched into an optical fiber bundle. The optical
fiber bundle delivers the light to the entrance slit of the spectrometer where the light is
split into a range of wavelengths that depend upon the spectrometer settings. The optical
fiber bundle also includes a single fiber for delivering the light output of a wavelength
calibration source, the HG-1 Cal Source. The spectrometer is mounted in the
Instrumentation Module.
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Science & Engineering Associates, Inc.
Final Report
Ocean Optics HG-1 Cal Source – The HG-1 Cal Source is a mercury-argon lamp used to
provide emission light with lines of known wavelength. It is mounted in the
Instrumentation Module. The HG-1 is energized and the system collects a spectrum of
this source just before, and immediately following the LIBS analysis of every sample.
This spectral data is archived with the spectral data from the sample for quality assurance
purposes.
Mitsubishi Robot Controller – The robot controller provides the primary interface
between the robot arm and the PC104 Computer and SX Chip Timing Controller. The
robot controller also stores the various robot programs used by the system during normal
operations. It is mounted within the Instrumentation Module.
Robot Arm & Hand Set – The robot arm and hand-set are mounted within the
CAM/Wipe module and are used as the primary motion control device in the system.
Specifically this includes rotating the Filter Carousel to the proper station, retrieving
filter cassettes from the Filter Carousel, placing them into and retrieving them from the
Air Sampling Station, placing them into and retrieving them from the Spark Chamber,
and disposing of the spent filter cassettes in the Spent Filter Receptacle following the
LIBS analysis.
Filter Carousel – The filter carousel is a removable carousel that holds the filter cassettes
prior to their use by the system. It is installed in the CAM/Wipe Module, and access is
provided through an access panel on the back of the monitor enclosure. The carousel
holds up to 60 Canberra filter cassettes of either the 47 mm or 25 mm variety. The
carousel is comprised of five columns with 12 levels each. The top most level of the
carousel is reserved for BLANK filter cassettes, while the bottom most level is reserved
for SPIKE filter cassettes.
Spent Filter Receptacle – The spent filter receptacle is a removable receptacle used to
collect the filter cassettes following the LIBS ana lysis. The receptacle is mounted on two
rails in the CAM/Wipe Module with access provided by an access panel on the right hand
side of the monitor. The receptacle holds three disposable cardboard tubes each of which
has a capacity of 20 filter cassettes.
Spark Chamber Ventilation Blower – A ring blower mounted in the CAM/Wipe Module
provides air- flow to ventilate the Spark Chamber and draw air through the filter cassette
during the LIBS analysis. This ventilation air is drawn from the CAM/Wipe Module
interior through a replaceable In-Line HEPA Filter into the lower portion of the Optics
Assembly and into the Spark Chamber. The line from the Spark Chamber passes into the
Spark Chamber In-Line Pre-Filter to remove the larger particles entrained in the air
stream from the Spark Chamber. The outlet line from the pre-filter is connected to the
inlet of a larger in- line HEPA filter to trap the smaller particles before the air stream
reaches the ring blower. The exhaust from the ring blower is dumped back into the
CAM/Wipe Module enclosure.
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Final Report
MB840-B Centrifugal Blower & HEPA Filter – The centrifugal blower and HEPA filter
are mounted in the CAM/Wipe Module, with the HEPA filter inlet face exposed to the
ambient environment. This blower provides an air- flow of approximately 15-20 CFM to
pressurize the CAM/Wipe Module and the Instrumentation Module and provide sufficient
cooling to operate the system in a minimal power state in the event that the Affinity
Chiller fails.
Affinity 2 kW Chiller – The Affinity Chiller is a separate unit connected to the main
monitor enclosure by an umbilical. The purpose of this chiller is to supply two LiquidTo-Air Heat Exchangers mounted within the Instrumentation Module with chilled water.
This heat extraction system provides the cooling capacity required to extract the heat
produced by the various components within the Instrumentation Module. The umbilical
is comprised of an outflow and return coolant line, as well as a signal line to
communicate the chiller status to the PC104 Computer.
Air Sampling Station – The air sampling station is mounted in the CAM/Wipe Module
and is comprised of the air sampling inlet nozzle and the filter cassette receiver assembly.
During collection of an air sample, a 25 mm filter cassette is placed in the filter cassette
receiver and a seal is formed between the front face of the filter cassette and the inlet
nozzle, and between the conical aperture in the base of the filter cassette and the filter
cassette receiver plumbing. The line connected to the filter cassette receiver passes to an
In-Line HEPA Filter, the TSI Flow Meter, a normally closed solenoid valve, through a
bulkhead fitting and to the inlet of a GAST 0523-101Q rotary vane air pump. The In-Line
HEPA Filter protects the flow meter from particulate matter in the event of a missing or
ruptured filter.
TSI Flowmeter – The TSI Flowmeter is mounted in the Instrumentation Module between
the air sampling station and the normally closed solenoid valve. This is a thermal mass
flowmeter that is also equipped with a barometric pressure transducer. Using the average
of a measurement of barometric pressure just before and just after collection of the air
sample, combined with a measure of the ambient air temperature provided by and
externally mounted RTD, the system corrects the integrated mass flow volume to a true
volumetric sampled volume. The beryllium mass resulting from the LIBS analysis of a
CAM sample is divided by this sample volume to give a beryllium concentration in the
ambient air in units of µg/m3 .
Ambient Air Temperature RTD – The ambient air temperature RTD is mounted in the
CAM/Wipe Module, with the RTD probe extending into the ambient air environment
near the air sampling inlet nozzle. It is used to measure the ambient air temperature for
the purposes of correcting the measured mass flow into a true volumetric flow volume.
Figure 4-5 shows the overall layout of the monitor. The monitor enclosure is divided into
two separate modules, the Instrumentation Module on the bottom, and the CAM/Wipe
Module on the top. Compare this with the block diagram presented in figure 4-4.
Contract DE-AC26-00NT40768
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Science & Engineering Associates, Inc.
Final Report
CAM/Wipe Module
Instrumentation Module
Figure 4-5: Drawing of the overall layout of the monitor enclosure
Figure 4-6 shows a drawing of just the Instrumentation Module so that the various
internal components can be readily shown.
Contract DE-AC26-00NT40768
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Science & Engineering Associates, Inc.
PC104 SB
Computer,
Relay, & I/O Boards
Chromex ¼ m
Spectrometer
Final Report
Andor CCD
Detector
Liquid-To-Air
Heat Exchangers
Laser Coolant
Fill Cap
HG-1 Optical
Cal Source
SX Chip
Timing Controller
Gast Air Sampling
Pump
Mitsubishi
Robot Controller
Big Sky Mini-Ice
Laser Cooling/Power
Supply
Hard Disk
Terminal
Blocks
Andor PCI
Interface Card
Figure 4-6: Cut-away view of the Instrumentation Module.
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Science & Engineering Associates, Inc.
Final Report
Figure 4-7 shows a cut-away view of the monitor as viewed from the left- hand side.
Note that none of the air plumbing, electrical cabling, nor fiber optic cabling is shown.
Spent Filter
Receptacle
Spark Chamber
Ventilation Pre-Filter
CAM
/
Module
Inlet HEPA
Air Sampling
Station
Wipe
System Ventilation
Exhaust Port
Laser Head
Optics
Assembly
Spark Chamber
Ventilation HEPA
LIBS Column
Spark Chamber
Ventilation
Blower
Spark Chamber
Filter Cassette
Receiver
Module Interface
HEPA
X-Y Stages &
Homing
Solenoids
Filter Cassette
Carousel
Robot Arm & Hand Set
Robot
Boot
Arm
Sealing
DC Power Supplies
& DC/AC Relays
Figure 4-7: Cut-away view of the monitor viewed from the left-hand side
Figure 4-8 shows a view of the right- hand side of the monitor with the panels removed.
The Air Sampling Inlet Nozzle is shown in the upper right portio n of the photo. The inlet
nozzle is mounted to the Filter Cassette Receiver, which is mounted to the frame of the
monitor. The step on the periphery of the inlet nozzle receives a gasket that provides a
seal between the nozzle and the right- hand side panel. 8-32 machine screws are used to
secure the panel to the inlet nozzle, as well as to the instrument frame.
Contract DE-AC26-00NT40768
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Science & Engineering Associates, Inc.
Final Report
Air Sampling Inlet Nozzle
In-Line HEPA for
Mass Flow Meter
CCD Support
Mount
Multi I/O Breakout
Box for Andor CCD
Figure 4-8: Photo of the right hand side of the monitor with the panels removed
4.1.3.2 Safety Interlock System
The beryllium monitor utilizes three separate interlock circuits to ensure operator safety.
One circuit is queried by the BeCAM software and is used to ensure that the system is
configured properly prior to the start of an analysis run. This interlock circuit uses
switches on each of the access panels in the CAM/Wipe Module to detect the presence of
these instrument panels, and switches to detect the presence of the two side instrument
panels on the Instrumentation Module.
The second interlock circuit monitors the status of the access pane ls and instrument
panels in the CAM/Wipe Module and is connected directly to the Mini-Ice
Power/Cooling Supply unit. If any of the switches in this circuit are open, the laser will
enter a fault condition, and no laser output can be achieved. The BeCAM software will
read this fault condition and display a message to the operator indicating the nature of the
fault. The Nd:YAG laser used in the unit is a Class IV laser, but the beam is completely
enclosed within an optical system and sample chamber, thus the SPARK I.D.™
Beryllium Monitor can be operated as a Class I laser system.
The third interlock circuit monitors the status of the access panels and instrument panels
in the CAM/Wipe Module and is connected directly to the robot controller door interlock
input. If any of the switches in this circuit are open, the robot will enter a fault condition,
Contract DE-AC26-00NT40768
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Science & Engineering Associates, Inc.
Final Report
and no robot movement can be achieved. The BeCAM software will read this fault
condition and display a message to the operator indicating the nature of the fault.
A CAUTION sign has been placed on each of the operator removable access panels to
remind the user that the system must be operated with all covers closed. Figure 4-9
shows the labling.
! CAUTION !
LASER RADIATION WHEN OPEN
AVOID EYE OR SKIN EXPOSURE
TO DIRECT OR SCATTERED
LASER RADIATION
Figure 4-9: Caution label affixed to all operator removable access panels
4.1.3.3 Air Sampling System
The function of the air sampling system is to provide a sampling inlet, a means of holding
the Canberra filter cassette in place on the sampling inlet, a pump to draw air through the
filter, a mass flow meter to quantitatively measure the total air sampled, an in- line HEPA
filter to protect the mass Flowmeter, a normally closed solenoid valve, and a bulkhead
fitting. An RTD to monitor the ambient air temperature supplements these components.
Figure 4-10 shows a schematic for the Air Sampling Station. Note that the components
are distributed over both the CAM/Wipe and Instrumentation Modules. This is in
keeping with the philosophy of segregating components for contamination control.
RTD
(Omega RTD-860)
With Omega Model
TX92-1 Transmitter
Instrumentation Module
Air Sampling Pump
Gast 0523-101Q-G588DX
CAM / Wipe Module
Inlet Nozzle
In-Line
HEPA Filter
Flow
Bulkhead
Pass-Thru
Fitting
Normally Closed
Solenoid Valve
ASCO 8210G95
TSI Model 4043
Mass Flow Sensor
Standard Flow 0 - 200 SLPM
Absolute Pressure (kPa)
Gas Temperature (Deg. C)
RS-232 Communication
to PC-104 Computer
Flow Direction
Filter Cassette
Receiver
Canberra
25 mm
Filter Cassette
Figure 4-10: Schematic of the air sampling station
The Inlet Nozzle and the filter cassette receiver together are referred to as the Air
Sampling Station. The filter cassette receiver is a spring- loaded platform that is designed
to receive the filter cassette from the robot. A retractable tongue & nozzle assembly
Contract DE-AC26-00NT40768
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Science & Engineering Associates, Inc.
Final Report
fitted into the receiver plate allow the air sampling plumbing to be sealed to the conical
aperture on the bottom of the filter cassettes. An O-Ring provides a face seal between the
front of the filter cassette and the inlet nozzle.
A TSI Model 4043 thermal mass flow meter is used to quantitatively measure the total air
sampled for each CAM sample obtained. Figure 4-11 shows a photo of this flow meter.
This flow meter is also equipped with a barometric pressure transducer and internal
temperature sensor. Since the flow meter returns flow result for standard conditions
based on TSI’s calibration protocol, the results must be corrected to a true volumetric
basis for the ambient conditions at the time of sample acquisition. What is needed to
accomplish this, is the ambient temperature, and the ambient barometric pressure. The
external RTD temperature sensor provides an accurate ambient temperature
measurement, and the barometric pressure sensor within the flow meter can be used to
measure the ambient barometric pressure immediately before and after each CAM air
sample.
The air-sampling pump was mounted externally to the monitor enclosures partly as a
tactic to reduce the internal heat load, and partly for flexibility in operation of the
monitor’s CAM mode. By the incorporation of the normally closed solenoid valve
between the pump and the flow meter, it is possible to replace the pump with a house
vacuum as the airflow source. The tubing between the pump and the bulkhead fitting is
replaced with tubing routed to the house vacuum source. No other changes are needed.
The solenoid valve isolates the house vacuum from the rest of the air sampling system
until the start of an air-sampling interval.
Figure 4-11: TSI Model 4043 thermal mass Flowmeter.
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Final Report
4.1.3.4 LIBS Column
As implied by the name, the LIBS Column is a sub-assembly dedicated to the LIBS
analysis process. Figure 4-12 shows a photo of the LIBS column with many of the
components identified. The basic design approach to conducting the LIBS analysis was
to move the filter cassette containing the filter sample under a fixed laser beam to
produce a sparking pattern that would adequately interrogate the filter for beryllium. For
a number of reasons it was decided that the filter should lie in a horizontal plane during
the LIBS analysis process. To minimize the number of optical elements exposed to the
very high energy density of the YAG laser beam, it was decided to mount the laser head
vertically. In this way only one focusing optic would be in the beam path of the laser.
This simplifies alignment and maintenance requirements of the LIBS column, as well as
reducing the probability of laser damage to optics due to dust etc collecting of the optics.
Big Sky
Laser
Head
Laser Shutter Indicator
LIBS Support Frame
Emission
Collection
Fiber Optic Bundle
Spark
Chamber
Ventilation Inlet
HEPA Filter
Lower Optics Wiper
Upper Optics
Assembly
Lower Optics
Assembly
Spark Chamber Grab
Handle for Robot
Spark Chamber
Spark Chamber
Homing
Solenoid
For the Y-Axis
Filter Cassette
Receiver
Spark Chamber
Homing
Solenoid
For the X-Axis
Spark
Chamber
Home Solenoid
Figure 4-12: Components of the LIBS column
The foundation of the LIBS Column is a stiff LIBS support frame to which all other
components of the LIBS Column are attached. Two 1/8” dowel pins are used to align the
laser head to the remaining optical components. A co- linear optical design is employed
in the monitor. It is co-linear in that the optic axis of the laser beam is collinear with the
initial optical path of the emission collection optics. This design approach has a number
of advantages; chief among them is simplicity in aligning the emission collection optics
with the IR laser beam and the location of the spark. Figure 4-13 shows a diagram of the
co-linear optics system.
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Science & Engineering Associates, Inc.
Final Report
Laser Head
Emission Collection
Fiber Optic Bundle
Nd:YAG IR Laser Beam
45 Degree Mirror with a Hole
for the IR Laser Beam
1-Inch Optic
Focuses Laser Beam
Primary Emission Collection
½-Inch
Optic
AR
Coated
LIBS Plasma (Spark)
Created on Filter Surface
Spark Chamber
Filter Cassette
Figure 4-13: Diagram of co-linear optical system.
The Nd:YAG IR laser beam is emitted from the laser head, passes through a hole in a 45degree front-surface mirror, and is focused to a small spot on the top surface of the filter
by the 1-inch optic. The optical emission resulting from the plasma (spark) radiates out
in all directions from the plasma volume. The same 1- inch optic used to focus the laser
beam also serves to collect a portion of the emission light and direct it to the front surface
mirror, where it is reflected to a secondary focusing lens, the ½- inch AR coated lens.
These two lenses, acting together, collect light from the plasma (spark) and focus it onto
the end of the emission collection fiber optic bundle. The fiber optic bundle transmits the
collected light to the entrance slit of the ¼- meter spectrometer located in the
Instrumentation Module.
The 45-degree mirror is mounted in an adjustable mirror mount so that the hole may be
centered with the laser beam, and the collection optical system may be aligned with the
laser beam. Note that the 1- inch optic (a plano-convex lens) is tilted at an angle of 5
degrees with respect to the optic axis of the laser beam. This is done to prevent back
reflections from the flat surface of the lens from reaching the exit aperture optics of the
laser head and potentially damaging them. The 1- inch optic is also mounted in a
removable slide so that this lens may be easily cleaned and inspected for laser damage.
Figure 4-14 shows this removable slide. Note that the 45-degree mirror is located in the
Upper Optics Assembly, while the laser focusing lens is mounted in the lower optics
assembly.
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Science & Engineering Associates, Inc.
Seats for ball plungers are located
on the bottom of the slide
Final Report
Slide Dust Seal
Laser-Focusing Lens
Mounted
In
Removable
Slide
Figure 4-14: Removable laser focusing lens.
The Filter Cassette Receiver is a spring- loaded platform designed to allow the robot
grippers to load a filter cassette into an aperture in the bottom of the Spark Chamber and
seal a nozzle to the conical aperture on the bottom of the filter cassette. This nozzle is
connected to the Spark Chamber ventilation system and is used to draw air through the
filter during the LIBS analysis. The Spark Chamber is mounted to the Filter Cassette
Receiver. The entire Filter Cassette Receiver and Spark Chamber assembly is mounted
on a pair of spring- loaded X-Y slides that allow the assembly to be moved under the
fixed IR laser beam. The robot is the motion control device that is used to move this
assembly to produce the necessary sparking pattern. This is accomplished by having the
robot grip a handle attached to the Spark Chamber. It can then move the Spark Chamber
in the X-Y plane. A Spark Chamber Home Solenoid is used to lock the Spark Chamber
and Filter Cassette Receiver in the home position during loading and unloading of the
filter cassettes. A pair of solenoids, one for the X-Axis and one for the Y-Axis, are used
to assist the slide springs in returning the Spark Chamber/Filter Cassette Receiver to the
home position.
It is necessary to ventilate the Spark Chamber to prevent ablation debris from
accumulating on the bottom surface of the laser focusing lens and to prevent the build up
of beryllium contamination in the Spark Chamber that would lead to cross-contamination
between successive filter samples. Figure 4-15 shows a diagram of the Spark Chamber
ventilation scheme. Note the only the components associated with the LIBS column are
shown in figure 4-M. A diagram for the entire Spark Chamber Ventilation System is
shown in section 4.1.3.8. Note that air is drawn in past the bottom surface of the laser
focusing lens and down into the Spark Chamber. A skirt incorporated into the Spark
Chamber lid creates a narrow gap just above the top of the filter cassette. The annular
volume behind this skirt serves as a plenum and is depressurized by connection to the
vent system. This keeps the air velocity relatively high at the periphery of the filter
cassette, and therefore keeps ablation debris away from the filter cassette. Air is also
drawn through the filter media while it is situated in the Spark Chamber.
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Inlet HEPA Filter
Spark
Chamber
Final Report
Arrows Show
Direction of Air Flow
Spark Chamber Outlet & Nozzle
Outlet Connected to Spark Chamber
Ventilation System
Filter Cassette
Receiver
Figure 4-15: Spark chamber ventilation diagram.
The inlet HEPA filter is a precaution against the introduction of any foreign material
being drawn into the Spark Chamber and deposited onto the filter during the LIBS
analysis. A seal is also required between the moving Spark Chamber/Filter Cassette
Receiver and the Fixed Lower Optics Assembly. Although originally envisioned as a
flexible rubber boot, this concept proved difficult to implement in the space available.
An alternative approach was used. In this approach the top of the Spark Chamber is
configured with an F-1 felt washer as a face seal. A spring loaded Lower Optics Wiper is
attached to the Lower Optics Assembly and provides the dust seal against the F-1 felt
washer.
4.1.3.5 LIBS Timing
In order for the LIBS measurement process to be performed, a number of actions need to
be correctly timed with respect to each other. These include:
1. Moving the sample in the circular pattern
2. Triggering the CCD acquisition
3. Triggering the laser flash lamp
4. Triggering the laser Q-Switch
One approach to timing the sample movement with the laser is to move the sample to
each point to be interrogated in discrete steps with the robot, and then fire the laser to
conduct the LIBS analysis for that point.
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Final Report
The Big Sky laser used in this monitor requires a thirty shot, or more, warm- up of the
flash lamp prior to triggering the Q-Switch. This is necessary to allow the YAG rod to
reach thermal equilibrium prior to firing the Q-Switch. If thermal equilibrium is not
reached, thermal lensing effects of the rod end can result in damage to the laser output
optics. Recall that in a Q-Switched laser, laser output is only achieved when the QSwitch is triggered.
It was not feasible to incur the 30 shot warm- up before each LIBS analysis point on the
filter. There are 2,193 sparks required to analyze a 47 mm filter. With a 2 second period
for the 30 shot warm- up (30 shots / 15 Hz = 2 sec), 73.1 minutes would be required for
the LIBS analysis of each filter. So an alternative approach was used in which the 30
shot warm-up would be incurred only once for each filter to be analyzed. For this to be
feasible, it was necessary to be able to start the laser flash lamp and wait for the 30 shot
warm- up. Then, while the sample is being moved under the laser beam at an appropriate
rate, the Q-Switch triggering is enabled and disabled as appropriate to achieve the desired
sparking pattern. Note that when the Q-Switch is disabled, the laser flash lamp is still
running at 15 HZ to keep the YAG rod warm. With each Q-Switch trigger, the system
also needs to trigger the CCD detector to acquire the characteristic emissions from the
spark.
A circular sparking pattern was selected for several reasons. First and foremost, a pattern
comprised of a series of concentric circles that starts at the center of the filter can be
truncated at various numbers of circles to achieve different circle diameters. This allows
one basic pattern to be used for analysis of 25 mm, 37 mm, and 47 mm diameter filters.
Secondly, a circular sparking pattern fits a circular filter better.
Use of a fast, flexible dedicated microprocessor dedicated to this timing task was
necessary to keep the monitor’s computer system resources available for the data
reduction tasks and system monitoring and control. An SX28 microprocessor,
manufactured by Scenix was selected for this task. This microprocessor provides the
necessary control interface between the robot controller, laser and CCD detector. Figure
4-16 shows a block diagram of the components involved.
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Big Sky
CFR 200
Laser Head
Final Report
PFN
Laser I/O
PFN
Laser I/O
RS-232
Big Sky Laser
Mini- Ice
Power Supply
To COM-1
Ext. Trigger
Trig. Out
SX Q-Switch
Driver Circuit
Andor PCI
Detector I/O
Board
Fiber Optic For Opto Isolation
Auxout 1
Auxin 1
Ext Trig
Fire
Shutter
Sh. (30V)
To COM-3
RS-232
Q-SW Trig. Out
Andor Detector
Cable
A2
OK to Move From Circle #B
OK to Move From Circle #A
Andor
DB420-OE
CCD Detector
Fiber
Mitsubishi
CR1-571
Controller
SX Reset
Orbiting Circle #B
Orbiting Circle #A
Enable SX Chip
M_I7
M_I6
M_O4
M_O7
M_O6
M_O5
RB7
RA2
\MCLR
RB1
RB0
RB2
Fiber
CCD Trig. Out
OK to Move From Circle #B
OK to Move From Circle #A
Chip Reset
Orbiting Circle #B
Orbiting Circle #A
SX Enable
Flash Lamp Trig. Out
A1
Scenix SX 28
Microcontroller
Circuit
Figure 4-16: Block diagram of the SX28 microcontroller and associated
components
The robot controller drives four output lines to the SX 28 circuit (M_O4, M_O5, M_O6,
and M_O7). The SX 28 circuit drives two output lines to the robot controller (RA2 &
RB7), one output line to the Mini-ICE Laser Power Supply (A1), one output line to the
Andor Detector I/O board (A2), and an optical output (Fiber) to the SX Q-Switch Driver
Circuit. The Q-Switch Driver Circuit drives one output line to the Laser head to trigger
the laser Q-Switch.
The system control works as follows. With a filter cassette loaded in the Spark Chamber,
the system control software (BeCAMAppe.exe, operating on the PC 104 computer)
configures the laser for operation, and directs the robot controller to begin the LIBS
analysis via COM 3. That is, it launches a robot program that performs the orbit patterns
and interfaces with the SX 28 Circuit (2.prg). The system control software also passes a
variable telling the robot program how many orbits to perform.
Upon power up, the resident program on the SX chip waits for the Enable SX Chip line
(M_O5 – RB2) to be raised. Wherever this line is raised, the SX will drive the Flash
Lamp Trigger Out (A1) at 15.00 HZ to keep the laser flash lamp triggering at 15.00 Hz.
It also starts a 30-pulse count down, i.e. the 30 pulse warm-up. The robot program raises
the Enable SX Chip line (M_O5 – RB2), then grabs the spark chamber and moves the
filter to its center position (Orbit # 1) and raises the Orbiting Circle #A line (M_O6 –
RB0). This tells the program operating on the SX chip tha t the filter is in position and it
may run the timing necessary to produce the number of LIBS sparks for the first orbit,
which is one spark. Figure 4-17 shows a timing diagram for a spark sequence. When the
SX program has completed the required number of sparks, it raises the OK to Move from
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Circle #A line (RA2 – M_I6). The robot program reads the change in state of this line
and starts orbiting for orbit # 2 and drops the Orbiting Circle #A line (M_O6 – RB0).
When the robot is up to the required speed, it raises the Orbiting Circle #B line (M_O7 –
RB1). The SX program reads the change in state of the Orbiting Circle #B line (M_O7 –
RB1) and drops the OK to Move from Circle #A line (RA2 – M_I6) and begins generating
the number of sparks required for orbit # 2. The SX program uses a look- up table to
determine the number of sparks required for each orbit. When the required number of
sparks for orbit # 2 have been completed, the SX program raises the OK to Move From
Circle #B line (RB7 – M_O7). The robot program reads the change in state of this line
and starts orbiting for orbit # 3 and drops the Orbiting Circle #B line (M_O7 – RB1).
When the robot is up to the required speed, it raises the Orbiting Circle #A line (M_O6 –
RB0). The SX program reads the change in state of the Orbiting Circle #A line (M_O6 –
RB0) and drops the OK to Move from Circle #B line (RB7 – M_I7) and begins generating
the number of sparks required for orbit # 3. This handshake sequence between the robot
program and the SX program continues until the required number of orbits for the current
filter size have been completed. Then the robot program drops the Enable SX Chip line
(M_O5 – RB2) to discontinue output of the flash lamp triggering, and pulses the SX Reset
line (M_O4 - \MCLR) to restart the SX program.
Laser / CCD Detector Timing Diagram
25 Microsec.
1. Flash Lamp Trigger Pulse
257.5 Microsec.
100 Microsec.
2. Q-Switch Trigger Pulse
157.5 Microsec.
3. CCD Trigger Pulse
20 Microsec.
Time Scale in Microseconds
0
100
200
300
400
500
600
Figure 4-17: Laser / CCD detector timing diagram.
4.1.3.6 Carousel
To facilitate easy loading of the filter cassettes containing the wipe samples for a wipe
analysis, or unused filter media for a CAM run, some form of a removable filter cassette
magazine was required. Several different concepts were evaluated. The final design
utilizes a carousel arrangement. Figure 4-18 shows a photo of the Filter Cassette
Carousel used in the monitor.
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Rotating Handles Provide
Grip
Points for Robot Hand
Top Most Level Reserved
for BLANKS
Intermediate Levels Used for Unknowns
In Wipe Analysis Runs or Unused Filters
In CAM Runs
Bottom Most Level Reserved
for SPIKES
Spring Contacts Provide Connection Between the
Potentiometer and the Multi I/O Input of the
PC104 Computer
Figure 4-18: Filter cassette carousel used in the monitor.
The Filter Cassette Carrousel is configured with 5 columns (A – E) with 12 levels each,
for a total capacity of 60 filter cassettes. The top most level is reserved for BLANK
samples, and the bottom most level is reserved for SPIKE samples, leaving a capacity of
50 unknowns. The filter cassettes are registered in the proper position by a pair of
vertical rods for each column. The interior platter structure rotates relative to the support
structure. Spring- loaded ball plungers are used to provide detent positions in rotation.
The photo shows the carousel in what is called a full-detent position. In a full-detent
position a column is aligned with the vertical opening in the shield at the front of the
carousel, thereby allowing the robot are to retrieve cassettes from the column, Column A
in the photo. A half-detent position places the platter such that the opening in the shield
is half way between one column and the next. This has the advantage that the shield
keeps the filter cassettes from falling out of the carousel.
Again, the robot is the only motion control device used. Correspondingly, the robot is
also responsible for rotating the carousel as needed. The 5 handles mounted on top of the
carousel allow the robot hand grippers to grab the carousel and turn it from one detent
position to another.
A potentiometer mounted to the platter axel is used by the PC 104 computer to determine
the current location of the carousel. Three spring contacts located on the lower left part
of the carousel are used to connect the pot to the PC 104 computer when the carousel is
installed in the monitor. An access panel on the rear monitor enclosure panel provides
access to remove and replace the carousel. The carousel is mounted on four rails attached
to the monitor frame.
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4.1.3.7 Spent Filter Receptacle
Following analysis by the LIBS process, each filter cassette is retrieved from the Spark
Chamber and disposed of in the Spent Filter Receptacle by the robot. Figure 4-19 shows
a photo of the Spent Filter Receptacle. This assembly is comprised of a removable
enclosure that holds three disposable cardboard tubes, each capable of holding 20 used
filter cassettes. Three spring loaded slide drawers are located on the top most part of the
enclosure. These drawers serve to close off the cardboard tubes located within the
enclosure, except when a spent filter is being deposited into the tubes. The front cover
of the enclosure is easily removed using 6 quarter-turn fasteners to gain access to the
cardboard tubes. Following a run the tubes may be removed, a cap placed on the open
end, and the entire tube and spent filters disposed of a Be contaminated waste.
Alternatively, the tubes may be emptied of their spent filters and reused.
Disposable
Cardboard
Tubes
Spring-Loaded
Slide Drawers
Quick Remove
Front Cover
Figure 4-19: Spent filter receptacle used in the monitor.
4.1.3.8 System Ventilation
Figure 4-20 shows a schematic for the major airflow occurring within the monitor
enclosures. There are four major groupings related to airflow & ventilation within the
monitor. These are:
1. The Enclosure Ventilation System, comprised of the CAM/Wipe Module Inlet
HEPA Filter & Centrifugal Blower and the Module Interface HEPA Filter.
2. The Spark Chamber Ventilation System, comprised of the spark chamber inlet
HEPA filter, the Spark Chamber, the In-Line Prefilter, the In-Line HEPA Filter,
and the Fuji Regenerative Blower.
3. The Air Sampling System, comprised of the Air Sampling Station, and In-Line
HEPA Filter, The TSI Mass Flow Meter, a Solenoid Valve, and the GAST Rotary
Vane Air Pump.
4. The Air Circulatio n Fans on the Liquid-To-Air Heat Exchangers.
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Air Flow Schematic
Regenerative Blower
Fuji VFC 100P - 5T
Exhaust
CAM/Wipe Module
Enclosure
LIBS Column
Lower Optics
Assembly
Spark Chamber
Inlet HEPA Filter
In-Line
Pre-Filter
Fuji TX1215
Inlet
Spark Chamber
In-Line
HEPA Filter
Fuji IVF-23
Air Sampling
Station
Filter Cassette
In-Line
HEPA Filter
CAM/Wipe Module Inlet
HEPA Filter &
Centrifugal Blower
Moidule Interface
HEPA Filter
Liguid-To-Air
Heat Exchangers
Solenoid
Valve
TSI Model 4043
Mass Flow Sensor
Instrumentation Module
Enclosure
Standard Flow 0 - 200 SLPM
Absolute Pressure (kPa)
Gas Temperature (Deg. C)
RS-232Communication
to PC-104 Computer
Air Sampling Pump
Gast 0523-101Q-G588DX
Arrows Show Air Flow Direction
System Ventilation
Exhaust Port
Figure 4-20: Generalized air flow schematic for the monitor enclosure
The CAM/Wipe Module HEPA filter is the primary means of protecting the monitor
internals from airborne contamination in the operating environment. This HEPA filter is
mounted in an inlet plenum, with a small centrifugal fan drawing air through the filter
and pressurizing the monitor interior with several inches of water column pressure. All
other openings in the CAM/Wipe Module envelope are sealed under normal operations,
with the exception of the Air Sampling Station inlet. The Air Sampling Station Inlet
Nozzle is momentarily opened to the outside environment when a filter cassette is placed
into, or retrieved from the Air Sampling Station by the robot. At all other times this
orifice remains sealed, either by a seal between the back of the inlet nozzle and the filter
receiver, or by the back of the inlet nozzle and the face of the filter cassette currently
being used to acquire an air sample.
Pressurization of the CAM/Wipe Module by the centrifugal blower causes air to flow
through the Module Interface HEPA filter and into the Instrumentation Module, also
pressurizing it by several inches of water. This HEPA filter ensures that any beryllium
that may become loose in the CAM/Wipe Module does not reach the components in the
Instrumentation Module. Pressurization of the Instrumentation Module causes air to flow
into the bottom of the monitor/keyboard panel on the front of the monitor, and finally out
the System Ventilation Exhaust Port located on the upper left-hand side of this panel.
The restricted diameter of the exhaust port ensures that the CAM/Wipe Module and the
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Instrumentation Module will always be at a positive pressure with respect to the ambient
environment, so long as the centrifugal blower is operating.
As discussed in section 4.1.3.4, the purpose of the Spark Chamber Ventilation System is
to keep the laser-focusing lens clean, and prevent cross contamination between
successive samples. Figure 4-Q shows the entire Spark Chamber Ventilation system and
its relationship to the Enclosure Ventilation System. Note that the Spark Chamber
Ventilation System draws air in from the CAM/Wipe Module, and exhausts back to the
same module. This ventilation system is extensively filtered because the Spark Chamber
is a known source of beryllium contamination. The in- line pre filter is used to extend the
life of the In- line HEPA filter by trapping most of the larger particles ablated from the
filter during LIBS analysis.
4.2
System Control Software (BeCAMApp.exe)
4.2.1 Overview
The system control software (Be CAMApp.exe) controls the various hardware
components and provides an interface to the user. The software was written in Visual
C++, Microsoft Compiler Version 6.0. The user interface is comprised of three
components: operational set-up and run, data management, and system configuration.
There are two different operational functions: continuous air monitor or CAM mode and
wipe analysis mode. The system computer, on which this software operates, is a single
board computer based on the PC104 bus architecture with a 266 MHz Pentium processor.
The operating system is Microsoft Windows 98.
4.2.2 Software Architecture
The system supports three different operational modes: Continuous Air Monitor or CAM
Mode, Swipe Analysis Mode, and Calibration Mode. The CAM Mode allows the user to
set-up and execute a CAM run, the Swipe Analysis Mode allows the user to set-u and run
an analysis of swipe samples. The Calibration Mode allows the user to reprocess
previously collected data with a selectable calibration data file. In addition to these
operational modes, the user can select a Data Management option that allows the user to
select previously collected data and display the spectra for the sample. The System
Configuration option allows the user to change the various configuration settings for the
system. These include hardware settings such as which spectrometer grating, and
software settings such as which calibration data file to use and the CAM alarm threshold.
Each of these five modes is accessible from the start-up screen, shown in figure 4-21.
Detailed instructions for using the software to set-up and execute CAM and Swipe runs,
as well as using the Data Management and the System Configuration options are given in
the User’s Guide (Appendix B) and are, therefore, not repeated here.
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Figure 4-21: Start screen of the system control software.
4.2.2.1 State Diagrams
Figure 4-22 gives an overview of the top-level states of the system from the view of the
system operator.
4.2.2.2 Start State
On system power up, the computer is powered up and loads the operating system. The
operator selects the BeCAMApp.exe shortcut to start the software us ing a shortcut on the
desktop. The user can manually check for any of the system faults monitored through the
use of the Mode command, left menu item on the top menu bar.
4.2.2.3 Sample Handling Operational Modes
The Continuous Air Monitor and Swipe Analysis use the sample handling features of the
system and operate similar to each other. Figure 4-23 shows the sample handling state
transition diagram for these modes. The system uses the robotic arm to move filter
cassettes in the system and to position the filter during LIBS analysis. Prior to entering
sample operational mode, the program checks for operational faults including: carousel
installation and position, spent filter receptacle installation, chiller status, spark chamber
status, and pump station status. The system cools down the CCD detector and sets the
spectrometer.
4.2.2.4 Non-Operational States
Two administrative states allow the user to manage collected data and system
configuration to set operational parameters, including setting calibration data for data
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analysis and alarm set point levels. The system configuration is password protected.
4.2.2.5 Task Definitions
Figure 4-24 shows the program tasks, inter-process communication and task
synchronization and resource sharing. Inter-process sharing takes the form of message
queues, shared memory, semaphores and signals as supported by the operating system.
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Power Off
Systems Powered:
Computer/CCD Detector
Enclosure Ventilation
Spectrometer
Spark Chamber Ventilation
Power
Switch
Start State
Operational States
Sample
Handling
Operational
Modes
Continuous Air
Monitor
Swipe Sample
Calibration
User
Selection
Sample Handling
Transition
Check chiller status
Check carousel installation and position
Check gripper status
Check pump station status
Check spark chamber status
Check spent filter receptacle status
Check interlock status
Cool CCD Detector and set spectrometer
CAM
Setup
Swipe
Setup
Calibration
Setup
Non-Operational
States
Data
Management
System Setup
(Advanced User)
Figure 4-22: System state transition diagram.
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Sample Pump
Not Empty
Next Filter
Idle
Check Next
Filter Type
Sample Filter
Check
Pump
Station
Sample Pump Finished
Sample
Station
Empty
Spike, blank or
calibration
Move Filter Cassette from
Pump Station to LIBS Station
Move Filter Cassette from
Magazine to LIBS Station
Move Filter Cassette from
Magazine to Pump Station
LIBS Empty
LIBS Ready
Samples Left
in Magazine
Samples Remaining to Process
No More Samples
LIBS Analysis Sample
Positioning
LIBS Analysis Complete
Move Filter Cassette from
LIBS Station to Disposal
Figure 4-23: Sample handling state transition diagram.
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Message Queue
Alert/Alarm
Signal/Synchronization
Data
Resourc
e
User Interface
Run/Session
Setup
Data Transfer
Pump/Airflow
Fault Detection
Sample Control
Storage
Alerts
Airflow
Spectrometer
Ready
Robot
Data Storage
Next Posit ion
LIBS Analysis
CCD Detector
Data Ready
Operator
Update/Alarm
Data
Analysis
Trigger
Figure 4-24: Software task relationships.
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5 SYSTEM CALIBRATION
Calibration of the instrument can be broken down into several distinct areas. These are:
1. Calibration of the Mass Air Flow Meter
2. Calibration of the RTD & Transmitter for the Ambient Air Temperature
Measurement
3. Calibration of the LIBS Measurement Process
5.1 LIBS Calibration
5.1.1 Approach
The general approach used to develop a calibration model for the prototype instrument
was to use the Principal Component Analysis model developed during the Method
Development phase as a starting point and refine this as necessary to reflect any changes
in the spectral data exhibited by the prototype instrument. Recall that much of the work
performed during the Method Development Phase was acquired using either the
Continuim Laser and a the Arrick X-Y Stage for sample positioning, or the LIBS column
from the prototype instrument configured with an external ventilation system.
A series of samples, called the Calibration Samples, were prepared and analyzed using
the prototype instrument to produce the spectral data necessary to refine the calibration
model for the prototype instrument. Following analysis of the Calibration Samples,
another set of samples, the Validation Samples, were analyzed using the prototype
instrument. The results from the Validation Samples were reduced using the refined
calibration model, and compared against the known mass of beryllium deposited on the
filters. Several iterations of model refinement followed by data analysis of the spectra
from the Validation Samples data were used to arrive at the final calibration model used.
Filter samples of all of the beryllium mass loadings used for both the Calibration Samples
and Validation Samples were submitted to an analytical laboratory to verify the beryllium
mass deposited on the filters.
5.1.2 Spectral Data Structure and Processing
Raw data from a single sample on the Beryllium Analyzer come in an array of 32-bit
integers with 2193 (41 mm filter) or 653 (25 mm filter) single spark Laser Induced
Breakdown (LIB) spectra measured over 1024 wavelength channels. Ancillary
information carried along with the raw LIB spectra for each of the samples include:
•
•
•
Data file path – Location of raw data files on the computer
Data file name – File name assigned to the sample
Spectrometer Settings
o Entrance slit width
o Diffraction grating
o Center wavelength
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o Detector temperature setting
o Detector exposure time
Sample Parameters
o Run type – Air or Swipe samples
o Number of orbits – Number of concentric rings in the spark pattern
o Number of sparks – Total number of LIB spectra collected
o Calibration file – Name of instrument calibration file
o Number of samples – Total number of samples in this run.
Data are read into a Matlab® data structure containing the elements listed above. Custom
programs developed in the native Matlab ® language are used to load and display LIBS
data. For example plots may be produced which show the distribution of Beryllium on
the surface of the sample as in Figures 5-1 and 5-2.
Figure 5-1: Contour plot of beryllium surface distribution.
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Figure 5-2: Three-dimensional plot of beryllium surface distribution.
The intensity of the Beryllium emission line at 313 nm may also be plotted as a function
of spark number a shown in figure 5-3.
Figure 5-3: Spark series plot of Beryllium emission line intens ity.
All spectra collected on a filter sample may be plotted on a single axis as shown in figure
5-4. Also mean and standard deviation spectra can be plotted as in figure 5-5.
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Figure 5-4: All spectra from a sample plotted on a single axis.
Figure 5-5: Mean and standard deviation spectra for a calibration sample.
5.1.3 LIBS Data Analysis
The objectives of the data analysis are to develop a calibration for the instrument which
allows unattended analysis of samples for total mass of Beryllium, and to provide data
quality indicators for the mass estimate which allow the user be alerted when samples are
encountered which differ significantly from those that were used in the calibration (e.g.
new sample constituents found).
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5.1.3.1 LIBS of Calibration Samples
In order to provide quantitative estimates for the mass of Beryllium in the sample,
samples were prepared in the laboratory to allow development of calibration models. The
instrument is designed to scan a regular grid of points on the surface of the sample as
shown in figure 5-6.
LIBS Analysis
positions
Circular spark
pattern covers
entire filter surface
Sample of
Mass M
Sample
Cassette
Figure 5-6: Sample-sparking pattern.
Some assumptions during the calibration process are necessary in order to develop
methods of analysis for Beryllium mass detected.
•
•
•
The mass of Beryllium in the sample (M) is known.
The area where the sample is deposited is completely covered by the laser spark
grid (all Be mass is observed).
The error of the LIBS measurement is random (i.e. sample statistics represent the
population of measurements.)
Since the instrument collects single-spark spectra in the manner described above, a model
may be developed that estimates the quantity of Beryllium detected on a spark-by-spark
basis. This may be accomplished within the assumptions listed above since the total
mass of Beryllium on the sample is known, and the sparking pattern allows observation
using LIBS of the entire mass deposited on the sample. From this information, the
instrument response to Beryllium may be extracted for each single-spark spectrum. Then
the instrument response for each single-spark spectrum at the Beryllium emission
wavelengths, may be converted to an estimate for mass of Beryllium detected. Once the
estimated mass for each single spark is known, this information may be used to perform a
regression of the set of spectra against the mass detected. Thus a model is derived which
allows an estimate of Beryllium mass detected in each single spark spectrum.
To illustrate the process described in the previous paragraph, an example from the
calibration of the Beryllium analyzer using standard solutions is described below. First a
summary outline of the process is given to provide a framework for the example.
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1. Collect LIBS spectra for a set of samples over the range of interest for Beryllium
mass loading (e.g. 0-1µg Be.) During this time duplicate samples are run to
assess the instrument repeatability.
2. A duplicate set of the calibration samples is submitted for reference method
analysis (e.g. ICP-OES or ICP-MS) by an outside laboratory.
3. Extract the spectral variations (instrume nt response) associated with Beryllium for
each spark from one of the samples using Principal Components Analysis (PCA).
4. Use the PCA derived single-spark instrument response to Beryllium to estimate
the mass detected in each spark.
5. Perform a Partial Least Squares (PLS) regression of the raw spectra (X-block)
against the single-spark instrument response to Beryllium (Y-block).
6. Test the PLS model by using it to estimate samples which where not included in
the regression process.
7. Correct the PLS model for skew and bias to provide a more accurate estimate of
the mass of Beryllium detected.
LIBS spectra were collected for triplicate samples of six different Beryllium mass
loadings. A triplicate set of duplicates for these samples was submitted to an outside
laboratory for Beryllium analysis by ICP-OES. Table 1 lists the estimated amount of
mass deposited for each sample along with the average value for the mass on each sample
determined by the reference method (ICP-OES.)
Table 5-1: Beryllium Calibration Sample Data
Expected Be
Mass (µg)
0.0600
0.1300
0.1900
0.5100
1.0200
5.1.3.2 Reference Method
Average Be
Mass (µg)
2X Standard
Deviation
0.0587
0.1257
0.1840
0.5237
1.1000
0.0162
0.0150
0.0069
0.0214
0.1044
Figure 5-7 shows the average spectrum from each of the mass loadings. Figure 5-8 shows
an expanded view of the Beryllium region of interest for the average spectra of figure 57.
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Figure 5-7: Average LIBS spectra of calibration samples.
Figure 5-8: Expanded view of calibration samples in the Be spectral region.
5.1.3.3 Principal Components Analysis
From the set of mass loadings available, one is selected to be the calibration point for
developing the model of Beryllium mass for single-spark spectra. For this example the
1.020 µg sample was selected. Since there are triplicate sets of LIBS data available at
this mass loading, an average of the three sets of spectra is taken to form the 2193 X 1024
element (single sparks X wavelength channels) matrix of spectra for analysis by Principal
Components Analysis. The PCA results in a set of ortho-normal vectors that can be
interpreted as spectra, since the x-axis for these vectors is the wavelength axis of the
measured data. Figure 5-9 shows the second principal component (PC2) for analysis of
the average of the three LIBS data sets for the 1.020 µg sample.
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As can be seen in figure 5-9, that the PCA captured the spectral variations associated with
Beryllium almost exactly. This is evident by comparing the average spectra of Figures 57 and 5-8 to figure 5-9. Is it seen that the other atomic emissions observed during LIBS
of the filters are not included in PC2 from the PCA. Notice also in figure 5-9 that the two
prominent features of the “spectrum” occur at the wavelength channels centered on 313
nm and 332 nm, which are the atomic emission lines for Beryllium in this spectral region.
Therefore, the score associated with PC2 will be directly correlated to the amount of
Beryllium observed in each LIBS single-spark spectrum. Figure 5-10 shows the PC2
scores for each single-spark spectrum that correlate to the Beryllium mass detected.
Figure 5-9: Second principal component for 1.020 µg data set.
Figure 5-10: PC2 score for each single spark spectrum.
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5.1.3.4 Instrument Response to Beryllium
Using the assumptions listed in section 5.1.4, the relationship of the scores depicted in
figure 5-10 and the mass of Beryllium detected is accomplished. By assuming that the
mass of Beryllium on the sample is known, and all of the mass is observed, a closure
condition is reached where the area under the line plot of figure 5-10 is related to the total
mass of Be on the sample by a constant coefficient. This coefficient can be derived from
the data and a mass detected for each spark calculated as follows.
C=
M Be
∑ ( Si − S min )
i
mi = C ⋅ S i
Where :
mi = The mass of Berylli um observed in spark i
M Be = Total mass on the sample
S i = PCA derived Berylliu m score for spark i
S min = Minimum value of Beryllium sco res
Therefore, the Y-axis in figure 5-10 may now be plotted as Beryllium mass detected.
Figure 5-11 shows the result of recalibration of the Y-axis of figure 5-10.
Figure 5-11: Calibrated spark series plot.
5.1.3.5 Partial Least Squares Regression
Partial Le ast Squares regression was done to provide a single-spark prediction model for
Beryllium mass. The original set of raw spectra used in the PCA above was set as the Xblock and the data shown in figure 5-11 was used as the Y-block. Data were mean
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centered prior to running the regression. Figure 5-12 shows the Predicted Residual Error
Sum of Squares (PRESS) result for the PLS.
Figure 5-12: PRESS result from PLS regression.
As can be seen in figure 5-12, the global minimum in the PRESS result occurs at 11
latent variables. Since the PRESS increases with the higher order (>11 LVs) PLS
models, inclusion of more variables would only be an attempt at modeling the noise in
the data and would degrade the ability of the model to estimate beryllium mass from the
instrument response. Therefore, as shown in figure 5-12, 11 latent variables were chosen
for the PLS model. Figure 5-13 shows the regression coefficients for the 11- variable
model.
Figure 5-13: Regression coefficients for 11 latent variable PLS model.
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Examination of figure 5-13 shows that the regression achieved the desired result in that
the magnitude of the regression coefficients is essentially zero everywhere in the
wavelength domain with the exception of the 313 and 332 nm regions where the
Beryllium atomic emissions occur.
5.1.3.6 Calibration Model Testing and Validation
The predictive model for Beryllium mass was tested by using it to estimate the total mass
in each of the samples from the calibration set that were not used during the regression
process. Figure 5-14 shows a correlation plot of the estimated to actual mass of
Beryllium in each sample.
Figure 5-14: Estimated versus actual Beryllium mass for PLS model.
As can be seen in figure 5-14, there is a slight skew (slope error) and a small bias
(intercept error) to the PLS regression model. A correction was applied to the model to
compensate for the skew and bias errors. The resulting correlation plot is shown in figure
5-15.
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Figure 5-15: Correlation plot for skew and bias corrected model.
Figure 5-15 shows that the corrections to the PLS model have improved the ability of the
calibration to predict the mass of samples at 0.2 µg mass and below.
Since there are three replicate measurements for both the LIBS and reference method at
each of the calibration points, an estimate of the Limit of Detection and prediction error
can be done. Limit of detection is estimated by extrapolating the relationship between
the instrument response and Beryllium mass to zero, then taking the mass at which the
instrument response is 2 σ (σ = standard deviation) above the mean value of the
instrument detector noise. By plotting the average value of the three measurements for
both the LIBS and reference methods, 2σ error bars may be added for both the X- and Yaxes.
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2σ MDL = 0.0433 µg/sample
2σ MDL = 20 pg/spark
X-axis error bars represent 2σ of three replicate measurements with the reference method.
Y-axis error bars represent 2σ of three replicate measurements with the LIBS method.
Reporting limit for the reference method is 0.05 µg Be per sample.
Figure 5-16: Correlation plot with error bars for Beryllium Analyzer calibration.
The result of applying this process to a correlation plot of the corrected predictive model
is shown in figure 5-16.
5.1.4 Automated Beryllium Analysis
5.1.4.1 Automated Analysis Goals
Having developed a calibration model that relates instrument response to Beryllium mass,
an algorithm needs to be defined which will allow unattended analysis of samples. The
overall goals of the algorithm are as follows.
•
•
Quantify the mass of Beryllium
Extract information from spectral data which indicates:
o Data quality (e.g. detect instrument malfunctions)
o When samples contain constituents that have not previously been
observed.
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5.1.4.2 Automated Analysis Approach
As discussed above, the calibration model estimates mass of Beryllium from each singlespark-spectrum. Additional calculations are now to be added to the chain of events to
provide information on data quality and sample composition changes. Since the user of
the instrument is only concerned with the bulk values associated with the entire sample
and not the individual spark data, the following outline is set forth for the automated
analysis algorithm.
•
•
•
Each sample cassette that has been used to sample the airborne particulates or
take a swipe sample of a surface is subjected to LIBS where 2193 sample points
are sparked with the laser (single-spark spectra).
For each of the single-spark-spectrum a data classification and prediction
algorithm is applied to qualify the data for quantification of the Beryllium mass
detected.
Each of the quantities (e.g. Be mass detected) calculated from the single-spark
spectrum for a sample are combined to produce a composite result
A block diagram of the automated analysis algorithm is shown in figure 5-17.
LIB Spectra
One Per
Spark
Header Information
Ÿ
Ÿ
Ÿ
Sample Type
Filter type
etc.
LIBS Spectral Data
Processing Module
Sample
Acceptance
Score
(1)
Sample
Data Quality
Score
(1)
Sample
Beryllium
Score
(1)
Sample
Predicted
Beryllium
Mass (1)
Figure 5-17: Top level automated data analysis block diagram.
As shown in figure 5-17, there are three additional quantities calculated for each singlespark-spectrum from which composite values are computed for the entire sample. The
following outline summarizes the information in the figure above.
•
•
All values reported from the analysis are composite values for the entire sample;
data are not reported to the user on a spark-by-spark basis.
Beryllium Mass Quantification – Mass of Beryllium detected for each singlespark spectrum is estimated using a Partial Least Squares (PLS) regression model.
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•
Final Report
Mass estimates for all single spark spectra for a sample are added together to get
the total mass of Beryllium on the sample.
Data Acceptance – A primary and secondary data acceptance model is applied to
each single-spark spectrum
o Primary Data Acceptance – The purpose of this evaluation is to detect
(and possibly diagnose) instrument malfunctions. Data flagged as
unacceptable are separated out and are used to detect any degradation in
instrument performance.
o Sample Data Quality Score – This evaluation detects radical changes in
the chemical constituents in the sample matrix. Unrecognized spectra are
separated out from further automated analysis to be inspected off- line in
detail.
o Sample Beryllium Score – This parameter is for future use in the
development of advanced methods of improving the precision and
accuracy of the Beryllium quantity reported. At this time this value is
calculated but not used in the algorithm.
5.2 Flow Measurement Calibration
TSI recommends that the Model 4030 undergo factory recalibration on an annual basis.
Prior to shipment, an RMA number should be obtained from TSI. The unit should be
shipped to:
TSI Incorporated
500 Cardigan Rd.
Shoreview, NM 55126-3996
5.3 Air Temperature Calibration
The ambient air temperature that is used to correct the airflow measurement is obtained
with a 100 Ω platinum RTD probe and an Omega TX92-1 4-20 mA transmitter. Consult
the User’s Guide for the TX92-1 transmitter for a general discussion of calibration
procedures. The procedure detailed here assumes that a precision RTD simulator, such as
an Altek Series II RTD simulator, is available.
A 24 VDC power supply is used to power the TX92-1 transmitter current loop. A 250 Ω
precision resistor is used as a load in the current loop, and the voltage drop across the
resistor is measured using an analog input channel on the PC 104 Multi I/O board. The
high side of the resistor is connected to terminal # 8 of the Signal terminal block using an
orange wire. The low side of the resistor is connected to terminal # 9 of the same
terminal block using a blue wire. Figure 5-18 shows these connections. A voltmeter
connected to the screw terminals on the terminal blocks may be used to directly measure
the signal voltage seen by the PC 104 Multi I/O board.
The BeCAMApp.exe software uses the following relationship to reduce the input voltage
to a temperature in degrees C.
Temp Deg. C = 22.222 (Deg C/Volt) * X (Volts) + 62.222 Deg. C
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Calibration involves connecting a precision RTD simulator to the TX92-1 transmitter in
place of the RTD while monitoring the voltage across terminals 8 & 9. The RTD
simulator is set to its lowest temperature setting within the TX92’s operating range. The
ZERO pot of the TX92 is adjusted until the voltage measured across terminals 8 & 9
matches the theoretical value derived from the above relationship. The RTD simulator is
then set to its highest temperature setting that is within the range of the TX92’s operating
range. The SPAN pot of the TX92 is adjusted until the voltage measured across
terminals 8 & 9 matches the theoretical voltage derived from the above relationship.
Since the ZERO adjustment affects the SPAN and vica- versa, it is necessary to alternate
adjustment s back and forth until stable readings are obtained. The Table 3 gives the
various temperature settings available on the Altek Model 11-250 F in degrees F, the
corresponding temperature in Degrees C, and the theoretical voltage that should be
observed across terminals 8 & 9 when the ZERO and SPAN adjustments are made
correctly on the TX92.
Table 5-2: Temperature settings available on Altek Model 11-250 and
corresponding terminal voltages
Setting on Altek
Model 11-250F (Degrees F)
0
25
50
75
100
Degrees C
-17.778
-3.889
10.000
23.889
37.778
Theoretical Voltage
Terminals 8 & 9 (Volts)
2.000
2.625
3.250
3.875
4.500
Use the clamping screw to make
Electrical contact with the terminal
contact
GND (-) Lead To #9 (Blue Wire)
Input (+) Lead to #8 (Orange Wire)
Figure 5-18: Photo showing the voltage measurement points for TX92-1 calibration.
Figure 5-19 shows the TX92-1 transmitter, which is mounted on the back of the Air
Sampling Station mounting plate. Access to the TX92 can be achieved by removing
either the left or right side enclosure panels of the CAM/Wipe Module.
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Figure 5-19. The Omega TX92-1 RTD transmitter (4-20 mA Current Loop).
5.4 Air Sampling Inlet Calibration
In order for the beryllium mass results obtained with the LIBS analysis to be interpreted
correctly, the collection efficiency of the sample inlet must be determined. If, for
example the collection efficiency of the inlet nozzle were very poor, then a small mass
collected on the filter would equate to a much larger mass concentration in the air being
monitored.
The collection efficiency of the inlet nozzle design for the beryllium monitor was
measured at the Lovelace Respriatory Research Institute (LRRI), using the aerosol wind
tunnel. Figure 5-20 shows a photo of the inlet nozzle and the reference aerosol samplers
configured for testing in the wind tunnel.
Figure 5-20: Photo of inlet nozzle efficiency test configuration.
The procedure used by LRRI to measure inlet nozzle efficiency makes use of fluorescent
latex microspheres of the aerosol size of interest, 5 µm in diameter in this case. An
aerosol generator is used to produce a constant aerosol concentration of the microspheres
in the wind tunnel. Three reference samplers are placed to sample the air stream in the
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wind tunnel at the same lateral position as the inlet nozzle under test. Sampling is carried
out for approximately 20 minutes, using a free stream velocity in the wind tunnel of
approximately 1 m/s. Following the sampling, the samples are removed from the
reference samplers and the orifice under test. The mass of the fluorescent microspheres
collected on each filter is determined using a calibrated fluorometer. The collection
efficiency is then determined by calculating the ratio of the aerosol mass measured from
the orifice under test to that of the average of the three reference isokinetic samplers.
Table 5-3 shows the results of five separate runs used to characterize the inlet orifice used
in the beryllium monitor.
Table 5-3: Inlet nozzle collection efficiency measurement results
Run 1
Flow (STD L/min)
∆p ("water)
Rotameter (SCFH)
Fluorometer (mVolts)
Efficiency
Run 2
Flow (STD L/min)
∆p ("water)
Rotameter (SCFH)
Fluorometer (mVolts)
Efficiency
Run 3
Flow (STD L/min)
∆p ("water)
Rotameter (SCFH)
Fluorometer (mVolts)
Efficiency
Run 4
Flow (STD L/min)
∆p ("water)
Rotameter (SCFH)
Fluorometer (mVolts)
Efficiency
Run 5
Flow (STD L/min)
∆p ("water)
Rotameter (SCFH)
Fluorometer (mVolts)
Iso Sampler 1
14.46
3
37
12.3
94.37%
Iso Sampler 2
14.46
3
35
12.3
Iso Sampler 3
14.46
3
35
12
Be CAM Orifice
53
63
180
42.2
Iso Sampler 1
14.45
3
38
15.8
96.53%
Iso Sampler 2
14.45
3
35
15.8
Iso Sampler 3
14.46
3
36
15.8
Be CAM Orifice
53
80
175
55.9
Isokinetic Sampler 1 Isokinetic Sampler 2 Isokinetic Sampler 3 Be CAM Orifice
14.46
14.46
14.46
53
3
3
3
80
37
37
35
180
8.4
8.3
8.4
28.3
92.36%
Iso Sampler 1
14.46
3.5
37
11.3
90.77%
Iso Sampler 2
14.46
3.7
38
11.9
Iso Sampler 3
14.46
3
36
11.3
Be CAM Orifice
53
84
183
37.2
Iso Sampler 1
14.46
3.2
38
9.4
Iso Sampler 2
14.46
3
38
9.9
Iso Sampler 3
14.46
2
37
9.5
Be CAM Orifice
53
82.5
182
32.1
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Efficiency
Final Report
91.23%
Results
Average Efficiency
Standard Deviation
93.05%
2.39
The average of the five measurement runs, 93 %, was used in the data reduction to
correct the CAM measurement results for collection efficiency. This parameter is
editable by the advanced user, in the event that the inlet nozzle is changed, or needs to be
characterized for a substantially different aerosol size range.
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6 DEMONSTRATION MEASUREMENTS
Following completion of the initial calibration activities, the prototype monitor
underwent a demonstration held at the Lovelace Respiratory Research Institute. A
written test plan (Test Plan for A Demonstration of the SEA Beryllium Monitor for the
Rocky Flats Environmental Technology Site) was prepared for this activity. RFETS
personnel provided input to, and reviewed the plan prior to the commencement of the
demonstration activities. This document is presented in Appendix E.
6.1 Measurements At LRRI
The following is a brief summary of the activities conducted at the LRRI demonstration.
Three different sample groups were prepared and analyzed with the prototype monitor.
The first group, referred to as the Measurement Performance Samples, were samples
prepared from solution based beryllium standards on 47 mm Millipore RW-19 filter
media. These samples were run using the Canberra 47 mm filter cassettes. SEA was
responsible for the preparation of these samples. Three identical sets of samples were
prepared simultaneously. One set was allocated for analysis in the prototype monitor, a
second set was submitted to RFETS for analysis in a laboratory of their choice, and a
third set was retained by SEA and submitted to Assaigai Analytical Laboratories. Table
6-A shows the range of beryllium mass loadings used for these samples, and represents
the samples in one of the above sets. The mass loadings were selected to be
representative of what would be expected from CAM samples over the range of airborne
beryllium concentrations of interest to RFETS. Note that five replicates were prepared
for each Series #, resulting in 25 samples per set.
Table 6-1: Measurement performance samples
Series #
1
2
3
4
5
Equivalent Be
Airborne
Concentration
(µg/m3 )*
0.04
0.08
0.2
0.7
1.3
Beryllium Mass
Loading
(µg Be/Filter)
Number of
Replicates
0.03
0.06
0.15
0.51
1.02
5
5
5
5
5
Comments
RFETS Action Limit
The second sample group, referred to as the Synthetically Contaminated Wipe Samples,
was intended to demonstrate the wipe analysis function of the prototype monitor. These
samples were prepared using a procedure where a known mass of beryllium particulate
was deposited on a clean prepared surface, which was subsequently wiped using standard
dry wipe procedures, thereby transferring the beryllium to the filter media. A discussion
of the approach to this technique and a written procedure for this are given in Appendix
E.
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The alternative approach of directly depositing the particle suspension on the filter media
to be analyzed was considered, but rejected in favor of the actual wipe process. This was
due in large part to the non-uniform nature of the beryllium distribution on an actual wipe
sample. Whereas this is of little concern in the traditional analytical methods where the
entire wipe is digested prior to analysis, it is a potential issue with the prototype
beryllium monitor because of the sequential way in which the filter is analyzed.
47 mmWhatman-41 filter media was used for preparation of these samples. Particulate
beryllium suspensions were used as the source of beryllium deposited onto the aluminum
plates. These suspensions were prepared from the 2.5 – 5.9 µm aerodynamic particle size
range, i.e. stage 2. The spikes and blanks that were also run on the prototype monitor for
this analysis set were prepared using Millipore RW-19 filter media and solution based
standards. Analysis was carried out in the 47 mm filter cassettes.
Four identical sets of samples were prepared simultaneously. One set was allocated for
analysis in the prototype monitor, a second and third set were submitted to RFETS for
analysis in a laboratory of their choice, and a fourth set was retained by SEA and
submitted to Assaigai Analytical Laboratories. Table 6-2 gives the various mass loadings
used in the preparation of these samples.
Table 6-2: Beryllium mass loadings for synthetically contaminated wipe samples
Series
#
1
2
3
4
5
Target Be Mass/Area
(ng/cm2 )
0
0.5
1.0
2.0
20.0
Expected Be
Mass/Filter (µg)
0.0
0.05
0.1
0.2
2.0
Comment
Wipe in a Be Free Area
Half the RFETS Action Limit
The RFETS Action Limit
The third group, referred to as the RFETS Duplicate Wipe Samples, were just that, a
series of 20 pairs of wipe samples obtained by RFETS industrial hygiene personnel at the
Rocky Flats site. The duplicate pairs were obtained by having the individual hold a
Whatman 41 filter circle in each hand and placing the filters side-by side on the surface to
be sampled. Then, using a long “S” motion the surface was wiped encompassing
approximately 100 cm2 for each filter. Note that the traditional rectangular 100 cm2 was
not used. The objective of this procedure was to obtain a pair of wipe samples from real
environments at RFETS that would be comparable in beryllium abundance.
6.2 Analysis of Demonstration Results
6.2.1 Performance Samples
Five replicates of each beryllium- mass loading were submitted to Assaigai Analytical
Laboratories by SEA, and Johns Manville IH Laboratory by RFETS. Table 6-3 shows
the results reported by the respective laboratories as well as the results reported by the
prototype beryllium monitor.
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Table 6-3: Measurement results of the Performance Samples
Target
Beryllium
Mass
(µg/Filter)
Sample ID
for
Assaigai
Samples
Result
Reported by
Assaigai
(µg Be/Filter)
0.03
S6-0.03-03
ND
0.03
S6-0.03-06
ND
0.03
S6-0.03-09
ND
0.03
S6-0.03-12
ND
0.03
S6-0.03-15
ND
0.06
S6-0.06-03
0.054
0.06
S6-0.06-06
ND
0.06
S6-0.06-09
0.054
0.06
S6-0.06-12
ND
0.06
S6-0.06-15
0.05
0.15
S6-0.15-03
0.148
0.15
S6-0.15-06
0.120
0.15
S6-0.15-09
0.136
0.15
S6-0.15-12
0.114
0.15
S6-0.15-15
0.102
0.51
S6-0.51-03
0.495
0.51
S6-0.51-06
0.454
0.51
S6-0.51-09
0.516
0.51
S6-0.51-12
0.426
0.51
S6-0.51-15
0.320
1.02
S6-1.02-03
0.922
1.02
S6-1.02-06
1.08
1.02
S6-1.02-09
1.02
1.02
S6-1.02-12
0.797
1.02
S6-1.02-15
0.661
Note: ND = Below laboratory detection limit
Sample ID
for Johns
Manville
Samples
S6-0.03-02
S6-0.03-05
S6-0.03-08
S6-0.03-11
S6-0.03-14
S6-0.06-02
S6-0.06-05
S6-0.06-08
S6-0.06-11
S6-0.06-14
S6-0.15-02
S6-0.15-05
S6-0.15-08
S6-0.15-11
S6-0.15-14
S6-0.51-02
S6-0.51-05
S6-0.51-08
S6-0.51-11
S6-0.51-14
S6-1.02-02
S6-1.02-05
S6-1.02-08
S6-1.02-11
S6-1.02-14
Result
Reported by
Johns
Manville
(µg Be/Filter)
0.030
0.027
0.027
0.027
0.027
0.065
0.055
0.055
0.055
0.055
0.154
0.145
0.140
0.128
0.138
0.476
0.468
0.475
0.479
0.496
0.975
0.971
0.969
0.978
0.951
Sample ID
for
Prototype
Monitor
S6-0.03-01
S6-0.03-04
S6-0.03-07
S6-0.03-10
S6-0.03-13
S6-0.06-01
S6-0.06-04
S6-0.06-07
S6-0.06-10
S6-0.06-13
S6-0.15-01
S6-0.15-04
S6-0.15-07
S6-0.15-10
S6-0.15-13
S6-0.51-01
S6-0.51-04
S6-0.51-07
S6-0.51-10
S6-0.51-13
S6-1.02-01
S6-1.02-04
S6-1.02-07
S6-1.02-10
S6-1.02-13
Result Reported
by Prototype
Beryllium
Monitor
(µg Be/Filter)
0.059
0.055
0.059
0.056
0.062
0.111
0.089
0.095
0.101
0.101
0.231
0.219
0.248
0.202
0.227
0.571
0.605
0.565
0.663
0.572
1.015
1.159
1.085
1.061
0.951
As described in the demonstration test plan, the results of the Performance Samples
reported by the analytical laboratories were analyzed using conventional inferential
statistics to evaluate the agreement between the laboratories. The results were compared
for each of four different target Beryllium mass loadings. Assaigai did not report results
above their detection limit for the lowest beryllium mass loading of 0.03 µg Be/filter.
Consequently no comparison with Johns Manville results was possible at this beryllium
level.
To be able to perform a two-sample t-test it was first necessary to compare the variances
from the two labs at each of the beryllium mass loadings. This comparison is made using
the F Distribution with a 95% confidence level. The null hypothesis is stated as:
2
σ Assaigai
H0 : 2
=1
σ JohnsManville
With the alternative hypothesis stated:
σ 2Assaigai
Ha : 2
≠1
σ JohnsManville
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The results of the F Test were that the observed variances for the samples at mass
loadings of 0.06 and 0.15 µg Be/filter were statistically no different between the two
laboratories at the 95% confidence level, and those for the samples at mass loadings of
0.51 and 1.02 µg Be/filter were statistically different between the two laboratories at the
95% confidence level.
Next the results were evaluated using a two-sample t-test with a 95% confidence level.
Table 6-4 summarizes these results. The column labeled “t Probability” is the probability
that the two sample means are from the same population. Where this probability is
greater than 0.05, the conclusion is to fail to reject the null hypothesis. Where the sample
variances were found to be statistically no different, a pooled variance was used to
calculate the t statistic. Where the variances were statistically different, the non-pooled
variance form of the equation was used. The null hypothesis for the t-test was stated as
follows:
H 0 : µ Assaigai = µ JohnsManville
With the alternative hypothesis stated:
H 0 : µ Assaigai ≠ µ JohnsManville
In each of the four beryllium- mass loadings that could be evaluated, the conclusion was
to fail to reject the null hypothesis, i.e. the results of the two laboratories are not
statistically different from each other. The laboratory results were, therefore, pooled
before comparison with the results produced by the prototype monitor. The pooled
laboratory results were compared to the results produced by the prototype using a twosample t-test. As before, an F test was performed to determine whether the sample
variances were statistically different or not. The variances were not statistically different
between the pooled laboratory results and those from the prototype monitor for all four of
the different beryllium- mass loading values. A two-sample t-test, with a 95% confidence
level, was performed to compare the results from the pooled laboratory data with that
produced by the prototype monitor. The null hypothesis for this test was stated as:
H 0 : µ Pooled Laboratory = µ Monitor
With the alternative hypothesis stated:
H 0 : µ Pooled Laboratory ≠ µ Monitor
Table 6-5 summarizes the results of these evaluations. As can be seen in the far right
column the results for the first four beryllium- loading levels exhibited statistically
significant differences between the pooled laboratory results and the results produced by
the prototype monitor. The results for the highest beryllium loading, @ 1.02 µg Be/filter,
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showed no statistical difference between the laboratory and monitor results at the 95%
confidence level.
Figure 6-1 shows a plot of the entire set of results from the Performance Samples. The
circles are the results from the prototype monitor, the triangles are the lab results from
Assaigai, and the squares are the results from Johns Manville. All of the results exhibit
good correlation with changes in the beryllium spike value. The results from the
prototype monitor are noticeably biased slightly high, while the results from Assaigai are
slightly low. The Johns Manville results exhibit the lowest variance of the three sets of
three, and also show the best agreement with the beryllium spike value. It can be
generally concluded that the results of the monitor are very similar to the results obtained
from the analytical laboratories.
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Table 6-4: Statistical summary of the laboratory results of the Performance Samples
Assaigai
Target Be
Mass (µg)
0.03
0.06
0.15
0.51
1.02
Johns Manville
Lab
Lab
Lab Mean Standard
Lab
Lab Mean Standard
Lab
(µg)
Deviation Variance
(µg)
Deviation Variance
0.053
0.124
0.442
0.896
0.002
0.018
0.077
0.170
5.33E-06
3.30E-04
5.89E-03
2.87E-02
0.028
0.057
0.141
0.479
0.969
0.001
0.004
0.010
0.010
0.011
1.80E-06
2.00E-05
9.10E-05
1.09E-04
1.11E-04
Difference in
Means (µg)
t
Test Type
Be
Probability
F*
3.750
3.626
54.206
258.395
-
-0.004
-0.017
-0.037
-0.073
2
2
3
3
0.1778
0.1130
0.3484
0.3917
Decision
N/A
Fail to Reject H0:
Fail to Reject H0:
Fail to Reject H0:
Fail to Reject H0:
Test Type = 2 means that the sample variances are equal @ 95% C.L.
Test Type = 3 means that the sample variances are not equal @ 95% C.L.
Table 6-5: Statistical summary of the prototype monitor results compared with the pooled laboratory results
Prototype
Pooled Lab Results
Prototype Prototype
Lab
Target Be
Mean
Standard Prototype Lab Mean Standard
Lab
Mass (µg)
( µg)
Deviation Variance
( µg)
Deviation Variance
0.03
0.06
0.15
0.51
1.02
0.058
0.099
0.225
0.595
1.054
0.003
0.008
0.017
0.041
0.078
7.70E-06
6.12E-05
2.83E-04
1.68E-03
6.04E-03
0.028
0.055
0.133
0.461
0.932
0.001
0.004
0.016
0.055
0.120
1.80E-06
1.80E-05
2.67E-04
3.04E-03
1.43E-02
F*
4.278
3.403
1.060
1.807
2.366
Difference in
Means (µg)
Test Type
Be
2
2
2
2
2
0.031
0.044
0.093
0.135
0.122
t
Probability
1.79E-08
4.20E-08
1.31E-07
3.45E-04
6.10E-02
Decision
Reject H0:
Reject H0:
Reject H0:
Reject H0:
Fail to Reject H0:
Test Type = 2 means that the sample variances are equal @ 95% C.L.
Test Type = 3 means that the sample variances are not equal @ 95% C.L.
Contract DE-AC26-00NT40768
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RFETS Demo Performance Samples
1.400
Analytical Result (micrograms)
1.200
1.000
0.800
0.600
0.400
0.200
0.000
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
Spiked Be Mass (micrograms)
Monitor
1:1 Line
Assaigai Lab
Johns Manville Lab
Figure 6-1: Plot of the results for the Measurement Performance Samples
Contract DE-AC26-00NT40768
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6.2.2 Synthetically Contaminated Wipe Samples
Five replicates of each beryllium- mass loading in the Synthetically Contaminated Wipe
Samples were submitted to Assaigai Analytical Laboratories by SEA, and Johns Manville
IH Laboratory and DataChem by RFETS. Table 6-6 shows the results reported by the
respective laboratories as well as the results reported by the prototype beryllium monitor.
One of the questions to be answered was whether or not the procedure developed to
prepare these synthetically contaminated wipe samples worked very well. The general
criteria for success included:
1. A high transfer coefficient – This is that the procedure would result in a high
percentage of the spiked beryllium being transferred to the wipe filter. Initial
expectations were that the procedure would result in the transfer of between 75%
and 80 % of the spiked beryllium.
2. A consistent transfer coefficient - This is that the procedure would result in
approximately the same fraction of the spiked beryllium being transferred to the
wipe filter each time that the procedure was perfo rmed. The measure of this is the
standard deviation of the five replicated at a given beryllium- mass loading.
One of the reasons to use three analytical laboratories for the analysis of the Synthetically
Contaminated Wipe Samples was to ensure that it wo uld be possible to distinguish poor
laboratory performance from a high variability in the transfer of beryllium from the
aluminum plate to the wipe filter. In general the results from the laboratories show that
the procedure worked very well. Figure 6-2 shows a plot of all of the laboratory results.
A 1:1 line is also plotted on the graph. The data would fall on this line if 100 % of the
beryllium deposited on the plate had been transferred to the wipe filter. A linear
regression was performed on the data from each of the three laboratories. The resulting
equation and regression coefficient are also shown on the plot. The slope of the line is a
measure of the average transfer coefficient. It can be seen that for all three sets of results
that the transfer coefficient was above 80%.
A statistical analysis of the comparability of the results reported by the various
laboratories was performed. The approach was identical to that described for the
Performance Samples and is described in section 6.2.1. Each laboratory was compared to
the other two laboratories. The results of these two-sample t-tests are summarized in
tables 6-7, 6-8, and 6-9. Table 6-10 summarizes the mean and relative standard deviation
for the results from each laboratory by the beryllium mass used to spike the aluminum
plates. The relative standard deviation for the various laboratories, as shown in table 6-J,
gives an indication of the upper limit of the uncertainty in the transfer coefficient of the
technique. The ordinary variance due to the laboratory analyses is also included in these
values. Note that this ranges from 2.7% to 29.4%
Figure 6-3: Shows a plot of the results reported by the prototype monitor for the
Synthetically Contaminated Wipe Samples. These results are significantly different from
the laboratory reported values. Note that the results of the Spike samples that were run
Contract DE-AC26-00NT40768
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concurrently with these wipe samples, exhibit a similar relationship to the 1:1 line, as was
observed with the Performance Samples. There are two differences between the
Synthetically Contaminated Wipe Samples and the Performance Samples. First is the
filter media. The Performance Samples were prepared using Millipore RW-19 filter
media, while the Synthetically Contaminated Wipe Samples were prepared using
Whatman 41 filter media. Second was the source of beryllium used for sample
preparation. The Performance Samples were prepared using beryllium solutions to spike
the filter media, whereas the Synthetically Contaminated Wipe Samples were prepared
with beryllium particulate suspensions. While there are issues associated with the use of
Whatman 41 filter media, it is note likely that the filter media alone is responsible for the
significant underreporting observed by the prototype monitor for these samples.
Figure 6-4 shows the results of a series of particulate samples, the same particle size as
was used in the preparation of the Synthetically Contaminated Wipe Samples (2.5 – 5.9
microns), analyzed by the prototype monitor.
These results exhibit a similar
underreporting as was shown with the Synthetically Contaminated Wipe Samples.
.
Contract DE-AC26-00NT40768
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Table 6-6: Measurement results of the Synthetically Contaminated Wipe Samples
Beryllium Mass
Deposited on the
Plate
(µg/Filter)
Sample ID for
Assaigai
Samples
Result Reported
by Assaigai
(µg Be/Filter)
Sample ID for
Johns Manville
Samples
Result Reported
by Johns
Manville
(µg Be/Filter)
Sample ID for
DataChem
Samples
Result Reported
by DataChem
(µg Be/Filter)
0.0
SW2-0.0-04
ND
SW2-0.0-01
ND
SW2-0.0-02
ND
0.0
SW2-0.0-08
ND
SW2-0.0-05
ND
SW2-0.0-06
0.010*
0.0
SW2-0.0-12
ND
SW2-0.0-09
ND
SW2-0.0-10
0.010*
0.0
SW2-0.0-16
ND
SW2-0.0-13
ND
SW2-0.0-14
0.010*
0.0
SW2-0.0-20
ND
SW2-0.0-17
ND
SW2-0.0-18
0.010*
0.05
SW2-0.05-04
ND
SW2-0.05-01
0.029
SW2-0.05-02
0.044
0.05
SW2-0.05-08
0.062
SW2-0.05-05
0.025
SW2-0.05-06
0.049
0.05
SW2-0.05-12
0.062
SW2-0.05-09
0.023
SW2-0.05-10
0.052
0.05
SW2-0.05-16
0.054
SW2-0.05-13
0.022
SW2-0.05-14
0.052
0.05
SW2-0.05-20
0.056
SW2-0.05-17
0.040
SW2-0.05-18
0.047
0.1
SW2-0.1-04
0.104
SW2-0.1-01
0.077
SW2-0.1-02
0.11
0.1
SW2-0.1-08
0.100
SW2-0.1-05
0.081
SW2-0.1-06
0.10
0.1
SW2-0.1-12
0.056
SW2-0.1-09
0.061
SW2-0.1-10
0.12
0.1
SW2-0.1-16
0.103
SW2-0.1-13
0.061
SW2-0.1-14
0.091
0.1
SW2-0.1-20
0.106
SW2-0.1-17
0.060
SW2-0.1-18
0.11
0.2
SW2-0.2-04
0.176
SW2-0.2-01
0.141
SW2-0.2-02
0.20
0.2
SW2-0.2-08
0.205
SW2-0.2-05
0.174
SW2-0.2-06
0.21
0.2
SW2-0.2-12
0.226
SW2-0.2-09
0.255
SW2-0.2-10
0.20
0.2
SW2-0.2-16
0.214
SW2-0.2-13
0.144
SW2-0.2-14
0.21
0.2
SW2-0.2-20
0.210
SW2-0.2-17
0.135
SW2-0.2-18
0.20
2.0
SW2-2.0-04
1.71
SW2-2.0-01
1.41
SW2-2.0-02
1.9
2.0
SW2-2.0-08
2.14
SW2-2.0-05
1.90
SW2-2.0-06
1.9
2.0
SW2-2.0-12
1.84
SW2-2.0-09
1.96
SW2-2.0-10
1.5
2.0
SW2-2.0-16
1.75
SW2-2.0-13
1.63
SW2-2.0-14
1.9
2.0
SW2-2.0-20
1.65
SW2-2.0-17
1.34
SW2-2.0-18
1.9
ND = Below Laboratory Detection Limit
* = Result Lies Between the Laboratory Detection Limit and the Contract Required Detection Limit of 0.01 µg Be.
Contract DE-AC26-00NT40768
Sample ID for
Prototype
Monitor
Result Reported
by Prototype
Beryllium
Monitor
(µg Be/Filter)
SW2-0.0-03
SW2-0.0-07
SW2-0.0-11
SW2-0.0-15
SW2-0.0-19
SW2-0.05-03
SW2-0.05-07
SW2-0.05-11
SW2-0.05-15
SW2-0.05-19
SW2-0.1-03
SW2-0.1-07
SW2-0.1-11
SW2-0.1-15
SW2-0.1-19
SW2-0.2-03
SW2-0.2-07
SW2-0.2-11
SW2-0.2-15
SW2-0.2-19
SW2-2.0-03
SW2-2.0-07
SW2-2.0-11
SW2-2.0-15
SW2-2.0-19
0.007
0.008
0.007
0.007
0.010
0.028
0.024
0.038
0.030
0.037
0.043
0.049
0.037
0.035
0.035
0.064
0.088
0.074
0.056
0.032
0.318
0.243
0.182
0.235
0.388
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Lab Results for the Synthetic Wipe Samples
3
Assaigai
y = 0.9063x + 0.0069
2
R = 0.987
2.5
Data Chem
y = 0.9041x + 0.0127
2
R = 0.9893
Lab Result (micrograms Be)
2
Johns Manville
y = 0.8286x - 0.0084
2
R = 0.9658
1.5
1
0.5
0
0.00
0.50
1.00
1.50
2.00
2.50
3.00
-0.5
Be Mass Deposited on Plate (micrograms Be)
Assaigai
Data Chem
Johns Manville
Linear (Assaigai)
Linear (Data Chem)
Linear (Johns Manville)
1:1 Line
Figure 6-2: Laboratory results for the Synthetically Contaminated Wipe Samples
Contract DE-AC26-00NT40768
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Table 6-7: Statistical summary of the results from Assaigai Lab and Johns Manville Lab for the Synthetically Contaminated
Wipe Samples
Assaigai
Johns Manville
Lab
Lab
Target Be Lab Mean Standard
Lab Mean Standard
Lab
Lab
Mass (µg)
(µg)
Deviation Variance
(µg)
Deviation Variance
0.00
0.05
0.10
0.20
2.00
0.059
0.094
0.206
1.818
0.004
0.021
0.019
0.193
1.70E-05
4.51E-04
3.45E-04
3.72E-02
0.028
0.068
0.170
1.648
0.007
0.010
0.050
0.280
5.37E-05
1.03E-04
2.50E-03
7.82E-02
F*
3.159
4.381
7.230
2.103
Difference in
Means (µg)
t
Test Type
Be
Probability
-
2
2
2
2
0.031
0.026
0.036
0.170
0.0001
0.0399
0.1653
0.2955
Decision
N/A
Reject H0:
Reject H0:
Fail to Reject H0:
Fail to Reject H0:
Test Type = 2 means that the sample variances are equal @ 95% C.L.
Test Type = 3 means that the sample variances are not equal @ 95% C.L.
Table 6-8: Statistical summary of the results from Assaigai Lab and DataChem Lab for the Synthetically Contaminated Wipe
Samples
Assaigai
DataChem
Lab
Lab
Target Be Lab Mean Standard
Lab
Lab Mean Standard
Lab
Mass (µg)
(µg)
Deviation Variance
(µg)
Deviation Variance
0.00
0.05
0.10
0.20
2.00
0.059
0.094
0.206
1.818
0.004
0.021
0.019
0.193
1.70E-05
4.51E-04
3.45E-04
3.72E-02
0.009
0.049
0.106
0.204
1.820
0.001
0.003
0.011
0.005
0.179
1.80E-06
1.17E-05
1.22E-04
3.00E-05
3.20E-02
F*
1.453
3.692
11.507
1.162
Difference in
Means (µg)
t
Test Type
Be
Probability
-
2
2
3
2
0.010
-0.012
0.002
-0.002
0.0061
0.2803
0.8103
0.9868
Decision
N/A
Reject H0:
Fail to Reject H0:
Fail to Reject H0:
Fail to Reject H0:
Test Type = 2 means that the sample variances are equal @ 95% C.L.
Test Type = 3 means that the sample variances are not equal @ 95% C.L.
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Table 6-9: Statistical summary of the results from Johns Manville Lab and DataChem Lab for the Synthetically
Contaminated Wipe Samples
Johns Manville
DataChem
Lab
Lab
Target Be Lab Mean Standard
Lab
Lab Mean Standard
Lab
Mass (µg)
(µg)
Deviation Variance
(µg)
Deviation Variance
0.00
0.05
0.10
0.20
2.00
0.028
0.068
0.170
1.648
0.007
0.010
0.050
0.280
5.37E-05
1.03E-04
2.50E-03
7.82E-02
0.009
0.049
0.106
0.204
1.820
0.001
0.003
0.011
0.005
0.179
1.80E-06
1.17E-05
1.22E-04
3.00E-05
3.20E-02
F*
4.590
1.186
83.190
2.443
Difference in
Means (µg)
t
Test Type
Be
Probability
2
2
3
2
-0.021
-0.038
-0.034
-0.172
0.0004
0.0005
0.2011
0.2800
Decision
N/A
Reject H0:
Reject H0:
Fail to Reject H0:
Fail to Reject H0:
Test Type = 2 means that the sample variances are equal @ 95% C.L.
Test Type = 3 means that the sample variances are not equal @ 95% C.L.
Table 6-10: Co mparison of variability by laboratory for the Synthetically Contaminated Wipe Samples
Beryllium Mass
Deposited on the
Plate (µg/Filter)
0.05
0.1
0.2
2.0
Assaigai Laboratory
Mean
Relative
Standard.
(µg/Filter)
Deviation (%)
0.059
7.1
0.094
22.6
0.206
9.0
1.818
10.6
Contract DE-AC26-00NT40768
Johns Manville Laboratory
Mean
Relative
Standard.
(µg/Filter)
Deviation (%)
0.028
26.3
0.068
14.9
0.170
29.4
1.648
17.0
DataChem Laboratory
Mean
Relative
Standard.
(µg/Filter)
Deviation (%)
0.049
7.0
0.106
10.4
0.204
2.7
1.820
9.8
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Prototype Monitor Results for Synthetic Wipe Samples
2.000
1.800
Monitor Result (micrograms Be)
1.600
1.400
1.200
Spikes
1.000
0.800
0.600
0.400
0.200
0.000
0.00
0.50
1.00
1.50
2.00
2.50
3.00
Be Mass Deposited on Plate (micrograms Be)
SW2 Wipe Samples
1:1 Line
Spike Samples
Figure 6-3: Monitor results for the Synthetically Contaminated Wipe Samples
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Evaluation of Particulate Samples
0.250
Monitor Result (micrograms Be)
0.200
y = 0.0969x + 0.0236
2
R = 0.9751
0.150
0.100
0.050
0.000
0.00
0.50
1.00
1.50
2.00
2.50
Be Mass Deposited on Filter (micrograms Be)
Figure 6-4: Monitor results of particulate sample analysis.
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6.2.3 RFETS Duplicate Wipe Samples
As previously mentioned, RFETS personnel developed a procedure intended to produce
paired (duplicate) wipe samples from real world settings by simultaneously wiping a
target area with two wipes. Whatman 41 filter media was used for these samples.
Twenty such duplicate wipes were provided by RFETS for analysis by the prototype
monitor. The remaining wipe sample of the duplicate pair was submitted by RFETS to
an analytical laboratory for analysis. Table 6-11lists the results for these duplicate
samples.
Table 6-11: Results of RFETS Duplicate Samples
Sample ID
Monitor Result
(µg Be/Filter)
444-0108-2002-212-101
0.082
444-0108-2002-212-102
0.124
444-0108-2002-212-103
0.237
444-0108-2002-212-104
0.007
444-0108-2002-212-105
0.156
444-0108-2002-212-106
0.561
444-0108-2002-212-107
0.055
444-0108-2002-212-108
0.051
444-0108-2002-212-109
0.033
444-0108-2002-212-110
0.040
444-0108-2002-212-111
0.023
444-0108-2002-212-112
0.018
444-0108-2002-212-113
0.029
444-0108-2002-212-114
0.066
444-0108-2002-212-115
0.017
444-0108-2002-212-116
0.016
444-0108-2002-212-117
0.011
444-0108-2002-212-118
0.011
444-0108-2002-212-119
0.011
444-0108-2002-212-120
0.013
* Result Below Lab Detection Limit (0.1 µg Be)
RFETS Lab Result for
Duplicate
(µg Be/Filter)
0.34
0.48
2.69
0.10
0.78
1.66
0.25
0.49
0.19
0.29
0.10*
0.10*
0.10*
0.11
0.10*
0.10*
0.10*
0.10*
0.10*
0.10*
Figure 6-5 shows a plot of the RFETS Duplicate Wipe Samples. The trend exhibited by
this plot is similar to that observed with the Synthetically Contaminated Wipe Samples, in
that the prototype monitor is substantially under reporting the beryllium present on the
filter media. Note that the spikes that were run in conjunction with the RFETS Duplicate
Wipes were prepared using beryllium solutions, but Whatman 41 filter media was used
instead of the Millipore RW-19 as was used for the spikes in the previous analysis runs.
The plot shows that the monitor under reports the value of the spike as well in this
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instance. This has to do with the fact that the laser does not completely ablate all of the
filter media thickness on the Whatman 41 as it does with the Millipore RW-19. When
beryllium solutions are used to prepare the spike samples, the solution wets the entire
thickness of the filter media, thereby depositing beryllium throughout its thickness. This
results in a fraction of the beryllium that was deposited on the filter media not being
available to interact in the LIBS process.
RFETS DUP Wipe Samples
3.000
Monitor Result (micrograms Be)
2.500
2.000
1.500
Spikes
1.000
0.500
0.000
0.00
0.50
1.00
1.50
2.00
2.50
3.00
RFETS Lab Result (micrograms Be)
RFETS Duplicate Wipe Samples
15% Line
Figure 6-5: RFETS Duplicate Wipe Samples
6.3 Summary of the LRRI Measurement Results
The following general statements mad be made with regard to the results of the
measurements conducted during the demonstration at LRRI:
1. When the samples to be analyzed are prepared from solutions deposited on RW19 filter media, the instrument measurement performance exhibits good
agreement with the known beryllium mass deposited on the filter even at
beryllium levels below 0.05 µg Be/filter.
2. When the samples analyzed were prepared from beryllium particulate
suspensions, and deposited on Whatman # 41 filter media, the prototype monitor
significantly underreported the beryllium mass present on the filter.
3. Similarly, when typical wipe samples obtained from RFETS using Whatman # 41
filter media and standard wipe techniques were analyzed (the RFETS Duplicate
Contract DE-AC26-00NT40768
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Wipe Samples), the prototype monitor exhibited results that were significantly
below the true beryllium abundance.
The explanation for statement # 1 is straightforward. The prototype instrument does
exhibit repeatability in its LIBS performance. So when the sample analyzed matches the
characteristics of the samples used for calibration, acceptable results are obtained. Note
that this means that both the filter media, as well as the particle size of the beryllium must
match.
Statements 2 & 3 illustrate the principal difficulties in the calibration of the prototype
monitor in its present state. Although the filter media plays an important part in the
observed results from the Synthetically Contaminated Wipe samples as well as the
RFETS Duplicate Wipe samples, it is the particle size of the beryllium that is of the most
significance. An assumption was made during the development of the calibration models
that there would be no significant particle size effect in the instrument response (i.e. the
optical emission intensity at 313 nm) over the particle sizes expected on the filters. This
clearly was not the case. Subsequent analysis of samples prepared from particulate
suspensions of varying size cuts deposited on RW-19 filter media show a marked particle
size effect. Figure 6-6 shows a plot of data obtained from the monitor with samples from
four different particle size ranges. The size ranges are, 0.5 µm, 2.5-5.9 µm, > 5.9 µm,
and a mixture of equal parts by mass of the other three size cuts. Sample preparation of
these samples is described in Section 3.3.3.
Figure 6-6: Variation in instrument response with beryllium particle size.
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As can be clearly seen in figure 6-6, the smaller the particle size, the higher the
instrument response for a given beryllium mass deposited on the filter. A mechanism can
be envisioned that would produce the observed particle size effect. The degree to which
the beryllium particle is completely vaporized during the lifetime of the LIBS plasma is
the most probable mechanism for the observed particle size effect. The smaller particles,
exhibiting a much larger surface area-to volume ratio, can be expected to vaporize more
completely for a given plasma lifetime and average temperature than larger particles. It
is not, however, known whether or not this is in fact the mechanism operating to produce
the effect, or if it is the only mechanism of significance.
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7 SUMMARY
The U.S. Department of Energy, through contract # DE-AC26-00NT40768, requested
development of a beryllium monitor that is capable of being deployed under realistic field
conditions, that has the capability to detect and quantify beryllium contamination on
surfaces with a sensitivity of 0.2 µg/100 cm2 , or better, and can also be used to measure
airborne beryllium concentrations down to levels of 0.2 µg/m3 , with a near-real-time
alarming capability. SEA has designed, fabricated and tested such a beryllium monitor
under this contract.
Features of the resulting monitor include:
•
•
•
•
•
•
•
Operation as a continuous air monitor or a wipe analysis instrument to monitor
surface contamination,
Four minute media interrogation time for near real-time measurement results,
Detection limit at 1/10 permissible exposure level,
Portable unit designed for use in contaminated areas,
Incorporation of spikes and blanks for continuous validation of reliable operation,
User settable alarm point for administrative action levels,
Contained disposal unit for easy post-processing handling.
The monitor does exhibit a particle size dependency in the calibration factor that must be
addressed in the implementation protocols for the monitor. The monitor has also
exhibited excellent sensitivity at very low levels of beryllium. On an individual spark
basis the monitor has been shown to be capable of detecting particles containing as little
as a few 10’s of picograms of beryllium.
Figure 7-1: Photo of the completed beryllium monitor
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APPENDIX A – DESIGN REPORT
Contract DE-AC26-00NT40768
Page A-1
Science & Engineering Associates, Inc.
Final Report
APPENDIX B – USER’S GUIDE
Contract DE-AC26-00NT40768
Page B-1
Science & Engineering Associates, Inc.
Final Report
APPENDIX C – ENGINEERING DOCUMENTATIION
Contract DE-AC26-00NT40768
Page C-1
Science & Engineering Associates, Inc.
Final Report
APPENDIX D: SOFTWARE CODE
Contract DE-AC26-00NT40768
Page E-1
Science & Engineering Associates, Inc.
Final Report
APPENDIX E – DEMONSTRATION TEST PLAN FOR
RFETS
Contract DE-AC26-00NT40768
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