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Title: Single-channel beta-gamma coincidence detection of radioactive xenon using digital pulse shape analysis of phoswich detector signals

Abstract

Monitoring radioactive xenon in the atmosphere is one of several methods used to detect nuclear weapons testing. To increase sensitivity, monitoring stations use a complex system of separate beta and gamma detectors to detect beta-gamma coincidences from the Xe isotopes of interest, which is effective but requires such careful gain matching and calibration that it is difficult to operate in the field. To simplify the system, a phoswich detector has been designed, consisting of optically coupled plastic and CsI scintillators to absorb beta particles and gamma rays, respectively. Digital pulse shape analysis (PSA) of the detector signal is used to determine if radiation interacted in either or both parts of the detector and to measure the energy deposited in each part, thus using only a single channel of readout electronics to detect beta-gamma coincidences and to measure both energies. Experiments with a prototype detector show that the technique can clearly separate event types, does not degrade the energy resolution, and has an error rate for detecting coincidences of less than 0.1%. Monte Carlo simulations of radiation transport and light collection in the proposed detector were performed to obtain optimum values for its design parameters and an estimate of the coincidencemore » detection efficiency (82%-92%) and the background rejection rate (better than 99%).« less

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
885201
Report Number(s):
PNWD-SA-7428
Journal ID: ISSN 0018-9499; IETNAE; TRN: US200616%%381
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: IEEE Transactions on Nuclear Science; Journal Volume: 53; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE; BETA PARTICLES; CALIBRATION; DESIGN; DETECTION; EFFICIENCY; ENERGY RESOLUTION; MONITORING; NUCLEAR WEAPONS; PHOSPHORS; PLASTICS; RADIATION TRANSPORT; RADIATIONS; SENSITIVITY; SHAPE; TESTING; XENON; beta-gamma coincidence detection; digital pulse shape analysis; phoswich detector; radioxenon monitoring

Citation Formats

Hennig, Wolfgang, Tan, Hui, Warburton, William K., and McIntyre, Justin I. Single-channel beta-gamma coincidence detection of radioactive xenon using digital pulse shape analysis of phoswich detector signals. United States: N. p., 2006. Web. doi:10.1109/TNS.2006.870447.
Hennig, Wolfgang, Tan, Hui, Warburton, William K., & McIntyre, Justin I. Single-channel beta-gamma coincidence detection of radioactive xenon using digital pulse shape analysis of phoswich detector signals. United States. doi:10.1109/TNS.2006.870447.
Hennig, Wolfgang, Tan, Hui, Warburton, William K., and McIntyre, Justin I. Sat . "Single-channel beta-gamma coincidence detection of radioactive xenon using digital pulse shape analysis of phoswich detector signals". United States. doi:10.1109/TNS.2006.870447.
@article{osti_885201,
title = {Single-channel beta-gamma coincidence detection of radioactive xenon using digital pulse shape analysis of phoswich detector signals},
author = {Hennig, Wolfgang and Tan, Hui and Warburton, William K. and McIntyre, Justin I.},
abstractNote = {Monitoring radioactive xenon in the atmosphere is one of several methods used to detect nuclear weapons testing. To increase sensitivity, monitoring stations use a complex system of separate beta and gamma detectors to detect beta-gamma coincidences from the Xe isotopes of interest, which is effective but requires such careful gain matching and calibration that it is difficult to operate in the field. To simplify the system, a phoswich detector has been designed, consisting of optically coupled plastic and CsI scintillators to absorb beta particles and gamma rays, respectively. Digital pulse shape analysis (PSA) of the detector signal is used to determine if radiation interacted in either or both parts of the detector and to measure the energy deposited in each part, thus using only a single channel of readout electronics to detect beta-gamma coincidences and to measure both energies. Experiments with a prototype detector show that the technique can clearly separate event types, does not degrade the energy resolution, and has an error rate for detecting coincidences of less than 0.1%. Monte Carlo simulations of radiation transport and light collection in the proposed detector were performed to obtain optimum values for its design parameters and an estimate of the coincidence detection efficiency (82%-92%) and the background rejection rate (better than 99%).},
doi = {10.1109/TNS.2006.870447},
journal = {IEEE Transactions on Nuclear Science},
number = 2,
volume = 53,
place = {United States},
year = {Sat Apr 01 00:00:00 EST 2006},
month = {Sat Apr 01 00:00:00 EST 2006}
}
  • Monitoring radioactive xenon in the atmosphere is one of several methods used to detect nuclear weapons testing. To increase sensitivity, monitoring stations use a complex system of separate beta and gamma detectors to detect beta-gamma coincidences from the Xe isotopes of interest, which is effective, but requires such careful gain matching and calibration that it is difficult to operate in the field. To simplify the system, a phoswich detector has been designed, consisting of optically coupled plastic and CsI scintillators to absorb beta particles and gamma rays, respectively. Digital pulse shape analysis of the detector signal is used to determinemore » if radiation interacted in either or both parts of the detector and to measure the energy deposited in each part, thus using only a single channel of readout electronics to detect beta-gamma coincidences and to measure both energies. Experiments with a prototype detector show that the technique can clearly separate event types, does not degrade the energy resolution, and has an error rate for detecting coincidences of less than 0.1%. Monte Carlo simulations of radiation transport and light collection in the proposed detector were performed to obtain optimum values for its design parameters and an estimate of the coincidence detection efficiency (82-92%) and the background rejection rate (better than 99%).« less
  • The Comprehensive Nuclear-Test-Ban Treaty establishes a network of monitoring stations to detect radioactive Xenon in the atmosphere from nuclear weapons testing. One such monitoring system is the Automated Radio-xenon Sampler/Analyzer (ARSA) developed at Pacific Northwest National Laboratory, which uses a complex arrangement of separate beta and gamma detectors to detect beta-gamma coincidences from the Xe isotopes of interest. The coincidence measurement is very sensitive, but the large number of detectors and photomultiplier tubes require careful calibration which makes the system hard to use. It has been suggested that beta-gamma coincidences could be detected with only a single photomultiplier tube andmore » electronics channel by using a phoswich detector consisting of optically coupled beta and gamma detectors (Ely, 2003). In that work, rise time analysis of signals from a phoswich detector was explored as a method to determine if interactions occurred in either the beta or the gamma detector or in both simultaneously. However, this approach was not able to detect coincidences with the required sensitivity or to measure the beta and gamma energies with sufficient precision for Xenon monitoring. In this paper, we present a new algorithm to detect coincidences by pulse shape analysis of the signals from a BC-404/CsI(Tl) phoswich detector. Implemented on fast digital readout electronics, the algorithm achieves clear separation of beta only, gamma only and coincidence events, accurate measurement of both beta and gamma energies, and has an error rate for detecting coincidences of less than 0.1%. Monte Carlo simulations of radiation transport and light collection were performed to optimize design parameters for a replacement detector module for the ARSA system, obtaining an estimated coincidence detection efficiency of 82-92% and a background rejection rate better than 99%. The new phoswich/pulse shape analysis method is thus suitable to simplify the existing ARSA detector system to the level of a single detector per sample chamber while maintaining the required sensitivity and precision to detect radioactive Xenon in the atmosphere. Ely, J. H. et al (2003), “NOVEL BETA-GAMMA COINCIDENCE MEASUREMENTS USING PHOSWICH DETECTORS” in Proceedings of the 25th Seismic Research Review – Nuclear Explosion Monitoring: Building the Knowledge Base, LA-UR-03-6029.« less
  • Recently new high resolution brain PET and PET/SPECT tomographs have been discussed using phoswich detectors. The detector design is based on two layers of scintillation crystals in the z-axis with different physical properties, such as light decay time or light yield. This makes it feasible to assign the depth of interaction (DOI) information in order to be able to correct for spatial degradation in PET or to operate the detector in PET or SPECT mode. The pixel DOI detectors are cost effectively arranged in a block design. In this work the authors discuss the possibility of separating events from themore » two different layers in the time domain using pulse shape discrimination or in the energy domain using pulse height discrimination. Furthermore, they have investigated the feasibility of interdetector scatter suppression using pulse shape discrimination. The measurements have been done using a LSO/LSO high resolution PET detector, a LSO and GSO crystal in coincidence and a NaI(Tl)/LSO combined PET/SPECT detector. The investigations show that the pulse shape discrimination technique has a significant higher identification probability compared to the pulse height discrimination and does make a interdetector scatter detection feasible.« less
  • An expansion of the very successful coincidence method developed for the accurate absolute measurement of the decay rate of radioactive preparations is described. By utilization of a scintillation counter with a single-channel discriminator for the detection of the gamma radiation at the site of the counter tube, the decay rate of the isotope Mn/sup 56/ previously unaccessible to coincidence measurements, could be determined under favorable conditions to 1%. (tr-auth)
  • The Pacific Northwest National Laboratory has developed an Automated Radio-xenon Sampler/Analyzer (ARSA) for the Comprehensive Test Ban Treaty (CTBT) to measure four radio-xenon isotopes, 131mXe, 133mXe, 133Xe, and 135Xe, using a beta-gamma coincidence counting detector. Betas and conversion electrons are detected in a cylindrical plastic scintillation cell and gammas and x-rays are detected in a surrounding NaI(Tl) scintillation detector. A novel method to measure beta-gamma coincidences using a phoswich detector has been investigated.