coincidence simulation of a two-channel czt-based
TRANSCRIPT
INTRODUCTION The Comprehensive Test Ban Treaty Organization makes use of radioxenon detection systems in the International Monitoring System stations to watch for signs of nuclear weapons testing and undeclared facilities. Systems using beta-gamma coincidence detection have been shown to have significantly reduced background counts, and are thus able to detect trace amounts of atmospheric radioxenon. A prototype of a multi-element coplanar CZT that uses two face-to-face coplanar CZT crystals to measure beta-gamma coincidence events from atmospheric radioxenon was developed at OSU.
OBJECTIVES The CZT-based detection system was simulated using MCNP to find the response of the detector to the xenon radioisotopes of interest and also calculate the coincidence detection efficiency of the device for these radioisotopes. In this work, modeling results from 131mXe, 133mXe, and 135Xe are reported.
MCNP MODELING 1. DETECTOR GEOMETRY
Geometry of the CZT-based radioxenon detection system simulated in MCNP.
2. PTRAC CARD
To model β-γ coincidence events in the CZT crystals, the PTRAC card was used. PTRAC follows each particle individually and writes an output file containing the entire history of that particle including position of interaction, energy of the particle, and the history number. A Python code was . developed to parse the PTRAC files and extract the position of . . interaction, energy released in each CZT crystal, and the . history number of each event from the PTRAC files. β-γ . coincidence events were then extracted for events with the . same history number ( NPS number).
COINCIDENCE DETECTION
PYTHON ALGORITHMS RESULTS
135Xe 135Xe emits 250 keV gammas in coincidence with beta particles (maximum energy ~ 910 keV)
133mXe 133mXe emits 30 keV x-rays in coincidence with 199 keV conversion electrons. (a) Simulated beta/gamma coincidence spectrum of 133mXe (b) energy deposited by 133mXe coincident events in CZT1.
131mXe 131mXe emits 30 keV x-rays in coincidence with 129 keV conversion electrons.
(a) Simulated beta/gamma coincidence spectrum of 131mXe (b) energy deposited by 131mXe coincident events in CZT1.
Radioxenons coincidence detection efficiencies calculated using MCNP.
Coincidence Simulation of a Two-Channel CZT-based Radioxenon Detector Lily Ranjbar*, Abi T. Farsoni, Eric M. Becker, David M. Hamby
Oregon State University, Corvallis, OR
Abi Farsoni, [email protected]
Consortium for Verification Technology (CVT)
Radioxenon
Gas Cell
Coplanar CZT1
Radioxenon
Injection Tube
Start
Load β / CE
PTRAC file
Load γ / X-
rays PTRAC
file
Interaction in
CZT1/CZT2?
Yes Full Energy
absorption?
Yes
Calculate
Partial Energy
Absorption
No
Save β /CE
and γ/x-ray
Partial Energy
Absorption
Save β/CE
and γ/x-ray
Full Energy
Finish
No
Last NPS Next NPS
Ignore First
10 Lines
Flowchart of the Python algorithm to parse
the PTRAC output files.
Flowchart of the Python algorithm to extract coincident events.
CZT 1 CZT 2
β/CE γ/x-ray
γ/x-ray β/CE
Scenario No.1
Scenario No.2
Coincidence scenarios considered in
this simulation.
Isotope Half-life Coincident Energies
(keV) Type Intensity (%)
131mXe 11.9 d 30
129
K X-ray
CE
54.1
60.7
133mXe 2.19 d 30
199
K X-ray
CE
56.3
63.1
133Xe 5.245 d
31
81
45
346
K X-ray
Gamma
CE
Beta (endpoint)
48.9
37
54.1
99
135Xe 9.1 h 250
910
Gamma
Beta (endpoint)
99
97
250 keV γ-rays
134 keV Compton edge
γ-γ
coincidence
events
x-rays escape peak
(a) (b)
(a) (b)
(a) (b)
This work was funded in-part by the Consortium for Verification Technology under Department of Energy National Nuclear Security Administration award number DE-NA0002534.
Save γ Energy in
Array1, β Energy
in Array 2
Equal NPS?
Yes
Finish
No
Start
Last NPS Next NPS
Load β / CE
Energy Data in
CZT2
Load γ / X-rays
Energy Data in
CZT1
Yes
Next NPS
Equal NPS?
Load β / CE
Energy Data in
CZT1
Load γ / X-rays
Energy Data in
CZT2
No
Finish Last NPS
Save γ Energy in
Array 2, β Energy
in Array 1
Radioxenon Coincidence Efficiency (%)
131mXe 3.1
133mXe 2.7
135Xe 1.7
(a) Simulated beta/gamma coincidence spectrum of 135Xe (b) energy deposited by 135Xe coincident events in CZT1.
Unclassified