10/29/2015
Comparison of Uranium Analysis Techniques
Presented by Dr. Amir Mohagheghi
19 October 2015
Radiation Measurements Cross Calibration (RMCC) Annual Workshop
Abu Dhabi, UAE
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed
Martin Company, for the United States Department of Energy’s National Nuclear
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Security
Administration under contract DE-AC04-94AL85000. SAND2015-8896C.
Presentation Outline
• Nuclear Detection Methods
– Gamma Spectroscopy
– Alpha Spectroscopy
– ICP Mass Spectroscopy
• New Research Area: ATTA
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Gamma Spectroscopy Analysis
• The aim of gamma spectroscopy is to identify and
quantify isotopes that emit gamma or x-ray radiation.
• Typical gamma spectroscopy system consists of a
High Purity Germanium (HPGe) detector, graded
shielding, signal processing electronics, and the
control & analysis software.
• The sample is prepared by placing it in a calibrated
geometry (e.g. Marinelli Beaker) and then placed on
the detector for spectrum acquisition and analysis.
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Examples of Gamma
Spectroscopy Systems
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Examples of Prepared Samples
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Gamma Spectrum Example
K-40
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Gamma Spectroscopy Summary
• Advantages: Sample preparation is simple, fast analysis, can
look for a large number of isotopes (typically 50)
• Issues: The detection limit for U is high for water samples;
Interference (e.g. Ra-226 interference can inflate the U-235
values in soil samples); Careful sample preparation required
to match calibration standards.
• Typical Detection Limits for Soil
– U-238: 0.15 pCi/g (0.45 mg/g)
– U-235: 0.07 pCi/g (0.033 mg/g)
– U-234: 100 pCi/g (0.016 mg/g)
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Alpha Spectroscopy Analysis
Physical Preparation
(add tracer)

Separate Element of Interest

Deposit on a Filter
(or electroplate)

Analyze by Alpha
Spectroscopy
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Alpha Spectrum Example
U-235
U-234
U-232
U-238
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Alpha Spectroscopy Summary
• Advantages: Low detection limits and
selectivity
• Issues: Labor intensive; Longer analysis
times; Isotope ratio measurements will
need special attention; Mixed Waste
• Detection Limits for Soil:
– U-234: 0.01 pCi/g (1.6E-6 mg/g)
– U-235: 0.01 pCi/g (0.005 mg/g)
– U-238: 0.01 pCi/g (0.03 mg/g)
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Inductively Coupled Plasma
Mass Spectrometer (ICP-MS)
Focusing
Plates
Detector
Plasma
Sample
Chamber
Heating Coil
(RF Coupled)
Skimmer
Cones
Mass
Spectrometer
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Example Spectrum
(DOE-EML Test Filter)
U-235
Th-232
U-238
Pu-239
U-234
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ICP-MS (Perkins Elmer Elan
6100)
Procedure Validation
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ICP-MS Sample Preparation for Water
• Filter
(if necessary)
• Analyze
DL (ng/L) Precision
Accuracy
U-235
0.1
4%
-5%
U-238
2.0
3%
-4%
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ICP-MS Sample Preparation for Bioassays
• Mix 1 mL of
Urine with 1 mL
of Nitric Acid
and 18 mL of DI
Water
• Analyze
DL (ng/L)
Precision
Accuracy
U-235
2
3%
-2%
U-238
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4%
5%
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ICP-MS Sample Preparation For Soil
• Mix ~0.1 gram of soil
with 15 mL of Conc.
Nitric Acid, 5 mL DI
Water, 5 mL HF
• Digest using a
Microwave oven
• Volume up to 50 mL
using DI Water
• Take 5 mL and volume
up to 25 mL with DI
Water
• Analyze
ng/g
ICPMS
U-234
0.3
U-235
U-238
pCi/g
ICPMS
2
pCi/g
pCi/g
Gamma Alpha
150
0.01
0.3
0.001 0.08
0.01
8.0
0.003
0.01
0.5
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ICP-MS Method Summary
• Advantages:
– Low detection limits for long lived isotopes
– Accurate isotope ratios
– Simple sample preparation
• Issues:
– High DL for short lived isotopes
– U-238 background
– Isotopic interferences (e.g. U-238, Pu-238)
– Complicated instrument (high maintenance and
constant tweaking)
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Presentation Outline
• Nuclear Detection Methods
– Gamma Spectroscopy
– Alpha Spectroscopy
– ICP Mass Spectroscopy
• New Research Area: ATTA
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Atom Trap Trace Analysis (ATTA)
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ATTA uses light to slow atoms
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Atom in a laser
beam can
experience
10,000’s of
excitationemission cycles
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Emitting atom
Atom “slowing” transition
Absorption
Emission
3 Special case: Noble gas
must be in metastable state Slowing
transition
Step 2: Near-IR
photon
Metastable state
“Slowing” laser beam
Step 1: UV photon
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•
•
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Each photon transfers momentum (h/λ) to
the atom in the direction of the laser beam
When the photon is emitted, momentum (h/λ)
is released in an arbitrary direction
The net effect is to slow the atom in the laser
direction
Can also be
excited using
plasma discharge
Trapping
transition
Na
NG
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Atoms are counted in a 3D MOT
Atom counts
Detector
Signal
• Magneto-optical trap (MOT)
• Six laser beams push the atom
to the center
• A magnetic field “tunes” the
atom levels so the transition is
resonant with the laser if the
atom strays from center
• Thus, the atom is trapped at
center, where it emits light and
can be counted
• Only atoms and isotopes
excitable by the laser are
trapped and counted
Time
Flow of “slow”
atoms
3D MOT
Magnetic coil
Cooling laser beam
Atoms must be slowed prior to trapping
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ATTA System
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10/29/2015
‫شكرا لوقتك‬
Thank you for your time
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