Active Dosimeters
Federico Ravotti
CERN TS-LEA
CEM2 – Montpellier University
Maurice Glaser, Michael Moll
CERN PH-TA1
Outline
 Introduction;


Total Ionizing Dose (TID) measurement:
•
Radiation Field Effect Transistors (RadFETs);
•
Optically Stimulated Luminescent materials (OSLs);
1-MeV neutron equivalent fluence (Feq) measurement:
• p-i-n diodes & PAD structures;

Thermal neutrons detection (Fth);

Status Dec. 2004 & Conclusion.
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004
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Introduction
1) RADIATION DAMAGES can be caused by:
 Ionizing Energy Losses (IEL)  Total Ionizing Dose (TID);
 Non-Ionizing Energy Losses (NIEL)  1-MeV neutron eq. fluence (Feq).
2) Important to monitor separately TID, Feq and maybe Fth;
3) The best “dosimeter” for electronics is Silicon itself (or similar Zeff);
4) Accelerator environments are (t)  Active (“on-line”) monitoring;
5) Monitoring is NOT ONLY for radiation damage survey.
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Active Radiation Monitors
TID (GySi)
mainly charged particles and photons
Feq
mainly fast hadrons
Forward
biased
p-i-n
diodes
RadFETs
Optically
Stimulated
Luminescence
(OSL)
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-2
(cm )
Reverse biased
PAD structures
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RadFETs General
(1) e-/h+ pair generation;
(2) e-/h+ pair recombination;
(3) e- (~psec) / h+ (~sec) transport;
(4) hole trapping;
(5) Interface state delayed buildup.
VGS
SiO2
iD
Fixed iD  VGS growths  TID
Si
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RadFETs Details
 Dosimetric information kept stored;
 2 wires, long-distance readout;
 Sensitivity vs. Dynamic range is (dox);
 “Saturation problems” can arise at
high Feq if oxide is not well chosen!
 CERN-PH-EP-2004/045
 Limited lifetime  sensitivity loss
(saturation);
 Dynamic range up to 100 kGySi;
 Particle-dependent response:
 proper calibration!
 Several ways to reduce T influence;
 “Drift-up” when switched on:
 proper readout scheme!
 “Neutron insensitive” devices.
 Annealing and Interface States
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generation in oxides:
 selection on SiO2 “quality”;
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RadFETs Selection
Procedure
Response to single radiation
Response to
and Room Temp. Annealing
some particle
fields and at high
Accelerated
procedure
based on the
scaling
annealing t 
SiO2 “quality” evaluation
(Isochronal Annealing)
Response at Low Dose-
doses were
missing in
literature!
Rate in Mixed Environment
annealing T
Devices packaging options
TWO types recommended
for CERN purposes !
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RADWG-RADMON Workshop Day, 01/12/2004
Aim of the 2004
irradiation campaigns
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OSLs General
(collaboration with CEM2 – Montpellier University)
(1) e-/h+ pair generation and trapping;
(2) Infrared stimulation (800-1500 nm);
(3) Visible emission (500-700 nm).
Courtesy of L.Dusseau, CEM2
IR stimulation
Peak Amplitude increases
OSL
Photosensor
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linearly with TID
The readout completely reset
sec
the sensitive material!
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OSLs Details
 Sensitivity from 10 mGy to 102 Gy;
 Infinite lifetime (readout = reset);
 Zeff (~ 30) close to electronics;
 Response NOT particle-dependent;
 Different ways to built an OSL-based
active dosimeter.
 Complicate fading behaviour;
 The related sensor equipment for
active dosimetry must be radhard:
Main problem in the
development of this
 Intrinsically neutron insensitive:
 We make them sensitive!
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 Long-distance readout with 5 wires;
technology at CERN!
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Neutron-sensitive OSLs
FACILITIES
NEUTRON
SPECTRA
IRRAD2 Facility
TRIGA Reactor
OSL+B
OSL+PE
First measurements
match very well the
facility spectra
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OSL “on-line” approaches
Integrated Space
sensor based on
COTS (Version 2)
 “sandwich” LED / OSL / photo-sensor;
 LED current electronically controlled;
 Optimized for long-distance readout;
 Hardness in n field under investigation:
(tested for e,p up to Feq=1011 cm-2).
Courtesy of J. R. Vaillé, CEM2
OSLs deposed
on “radhard”
photo-sensor & LED
Fibred
system
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 Gain in sensitivity, reproducibility;
 Gain in radiation hardness.
 First prototype: 2.3 mV/cGy
 2 fibers inside 20m x  4mm2 pipe with OSL at one end;
 Stimulation = Laser 1060 nm; Light detection = PM.
 Less radhard constraints (PM/Laser not exposed!)
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p-i-n & PAD General
Displacement damage in high r Si-base
Macroscopic effects both linear with Feq
FORWARD BIAS
Fixed iF  voltage increase
VF
REVERSE BIAS
Chosen VR leakage current increase
iL
iF


Readout with fast pulse;
Sensitivity depends on:


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Injection level;
Base width (W).
VR


Readout under full depletion V;
Sensitivity depends on sensor
volume.
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p-i-n & PAD Details
FORWARD Operation
- vs. -
REVERSE Operation
 Current pulse;
 High voltage maybe needed.
 2 wires, long-distance readout;
 2 wires, more complicate read-out;
 Feq range dependent on diode W;
 Very wide Feq range;
 Typically ~ 1.5 mV / 108÷1010 cm-2;
 Typically ~ 2 nA / 1010 cm-2;
 Strong T dependence;
 Strong T dependence;
 Relative low room T annealing;
 Complex annealing behaviour;
 Possible to use COTS!
 Very reliable devices.
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Commercial p-i-n diodes
Commercial (thin base) BPW34F Feq = 2x1012  4x1014 cm-2
3 – USE CUSTOM-MADE DEVICES
Low Flux irradiation in PS-T7 2004
(Max Feq = 2x1012)
2 – STUDY BPW34F RESPONSE AT
DIFFERENT INJECTION LEVELS!
1 – PERFORM PRE-IRRADIATION ON BPW34F
Low Flux irradiation in PS-T7 2004
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Thermal n detection
1) OSL doped with
10B:
+ n  7Li + a + g (s2200 = 3840 b);

10B

Dose deposition in OSL by low range reaction fragments.

More: Ravotti, Glaser, et al., RADECS 2004, CERN-PH-EP-2004/022
2) Damage in npn bipolar transistors:

Boron is usual dopant in p-type Si;

Fragment produce bulk damage in transistor base;

Increase of ib for fixed ic  Dib = kth· Fth+ keq· Feq

More: Mandic, Kramberger, et al., ATLAS-IC-ES-0017 (EDMS 498365).
3) 100-mm layer Fission converter on Silicon:

235U

Very high LET fragments  efficient discrimination in mixed field.

More: Rosenfeld, Kaplan, et al., Med. Phys. 26(9), pp. 1989, 1999
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+ n  140X + 95Y + 2n (s2200 = 580 b);
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Status Dec. 2004
 RadFETs:
9 devices from 4 producers tested: We recommend two types of RadFETs
for low (100m Gy ÷ 10 Gy) and high (1 cGy ÷ 10 kGy) dose ranges;
 OSLs:
Need some more development for use as radhard active dosimeter;
 p-i-n diodes:
 COTS devices: ready to be used, some optimization needed;
 Custom-made devices: ready to be used;
 PAD structure:
 Dedicated batch of devices to be produced;
 Thermal neutron detectors:
 OSL and diodes with fission converter: working principle shown;
 npn bipolar transistors ready to be used (ATLAS).
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Conclusion
 Several techniques for the ACTIVE monitoring of the TID, Feq and Fth
have been presented;
 All presented devices are reliable and were characterized in various
radiation fields;
 Most of them are commonly used in Medicine and Space:
customization and calibration for CERN applications needed;
 ACTIVE monitors are also PASSIVE dosimeters (don’t forget it !!)
More on: http://cern.ch/lhc-expt-radmon & http://www.cern.ch/irradiation
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Acknowledgments
Pr. L. Dusseau, J.R. Vaillé and all the team of the “Electronic and Radiation
research Laboratory” at the CEM2, Montpellier University, France;
I. Mandić, G. Kramberger, M. Mikuž from JSI, Ljubljana, Slovenia;
A.G. Holmes-Siedle (REM, UK), G. Sarrabayrouse (CNRS-LAAS, France),
A. Rosenfeld (CMRP, Australia);
C. Joram, E. Tsesmelis and all the personnel of the PH-Bonding Lab (CERN);
All the operators of the CERN-PS accelerator for their assistance during the
experiments.
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