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Title: {sup 6}LiF:ZnS(Ag) Neutrons Scintillator Detector Configuration for Optimal Readout

Abstract

A Chromatic Analysis Neutron Diffractometer Or Reflectometer (CANDOR) is under development at the NIST Center for Neutron Research (NCNR). The CANDOR neutron sensor will rely on scintillator material for detecting the neutrons scattered by the sample under test. It consists of {sup 6}LiF:ZnS(Ag) scintillator material into which wavelength shifting (WLS) fibers have been embedded. Solid state photo-sensors (silicon photomultipliers) coupled to the WLS fibers are used to detect the light produced by the neutron capture event ({sup 6}Li (n,α) {sup 3}H reaction) and ionization of the ZnS(Ag). This detector configuration has the potential to accomplish the CANDOR performance requirements for efficiency of 90% for 5 A (3.35 meV) neutrons with high gamma rejection (10{sup 7}) along with compact design, affordable cost and materials availability. However this novel design includes challenges for precise neutron detection. The recognizing of the neutron signature versus the noise event produce by gamma event cannot be easy overcome by pulse height discrimination obstacle as can be achieved with {sup 3}He gas tube. Furthermore the selection of silicon photomultipliers (SiPM) as the light sensor maintains the obstacle of dark noise that does not exist when a photomultiplier tube is coupled to the scintillator. A proper selection ofmore » SiPM should focus on increasing the output signal and reducing the dark noise in order to optimize the detection sensitivity and to provide a clean signal pulse shape discrimination. The main parameters for evaluation are: - Quantum Efficiency (QE) - matching the SiPM peak QE with the peak transmission wavelength emission of the WLS. - Recovery time - a short recovery time is preferred to minimize the pulse width beyond the intrinsic decay time of the scintillator crystal (improves the gamma rejection based output pulse shape (time)). - Diode dimensions -The dark noise is proportional to the diode active area while the signal is provided by the WLS fibers; therefore the diode area should ideally be only minimally larger than fiber bundle area. - Low dark noise - it is desirable to minimize the dark noise during the pulse integration period so as to minimize the background for pulse shape discrimination. - Photon Detection Efficiency - it is desirable to increase the SiPM PDE in order to enhance light collection. This will increase the likelihood of detecting neutron events with lower light production and will present a cleaner raw signal for pulse shape discrimination. We will present the SiPM optimization process and studies of dark noise and gamma and neutron sensitivity as a function of bias voltage and operating temperature that have enabled us to optimize the detector sensitivity and gamma rejection. The gamma rejection performance goal requires to overcome the challenge of discriminating between the light signature accepted by neutron event to the one received by the noise. In addition there is a huge variation between the number of light photons that reaching the WLS fibers for different neutron events caused by the heavy ions energy losses prior to ionizing the ZnS(Ag) and the high light attenuation of the scintillation mixture. This variation in the light signal along with the long decay time of the ZnS(Ag) (tens of microseconds) can cause double counting of the same neutron event in the case of high light output signature or preventing the detection of low sequential light output signature neutron event. We will presents the algorithm developed for {sup 6}LiF:ZnS(Ag) sensor readout and the results achieved by an off-line analysis by Matlab software code that successfully achieved both the high gamma rejection with a sensitive and accurate neutron event detection. (authors)« less

Authors:
 [1]; ; ; ;  [2]; ; ; ; ;  [1]
  1. NIST Center for Neutron Research, Gaithersburg, Maryland (United States)
  2. Nuclear Research Center Negev, Beer-Sheva (Israel)
Publication Date:
Research Org.:
Institute of Electrical and Electronics Engineers - IEEE, 3 Park Avenue, 17th Floor, New York, N.Y. 10016-5997 (United States)
OSTI Identifier:
22531441
Report Number(s):
ANIMMA-2015-IO-52
TRN: US16V0414102382
Resource Type:
Conference
Resource Relation:
Conference: ANIMMA 2015: 4. International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications, Lisboa (Portugal), 20-24 Apr 2015; Other Information: Country of input: France
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; DESIGN; ENERGY LOSSES; FIBERS; LITHIUM 6; MEV RANGE; NEUTRON DETECTION; NEUTRON DETECTORS; NOISE; PARTIAL DIFFERENTIAL EQUATIONS; PHOTOMULTIPLIERS; PULSE SHAPERS; QUANTUM EFFICIENCY; READOUT SYSTEMS; SCINTILLATION COUNTERS; SENSITIVITY; SENSORS; SI SEMICONDUCTOR DETECTORS; SILICON; VISIBLE RADIATION; ZINC SULFIDES

Citation Formats

Osovizky, A., Rotem Industries Ltd, Rotem Industrial Park, University of Maryland, College park, Maryland, Yehuda-Zada, Y., Ghelman, M., Tsai, P., Thompson, A. K., Pritchard, K., Ziegler, J. B., Ibberson, R. M., Majkrzak, C. F., and Maliszewskyj, N. C. {sup 6}LiF:ZnS(Ag) Neutrons Scintillator Detector Configuration for Optimal Readout. United States: N. p., 2015. Web.
Osovizky, A., Rotem Industries Ltd, Rotem Industrial Park, University of Maryland, College park, Maryland, Yehuda-Zada, Y., Ghelman, M., Tsai, P., Thompson, A. K., Pritchard, K., Ziegler, J. B., Ibberson, R. M., Majkrzak, C. F., & Maliszewskyj, N. C. {sup 6}LiF:ZnS(Ag) Neutrons Scintillator Detector Configuration for Optimal Readout. United States.
Osovizky, A., Rotem Industries Ltd, Rotem Industrial Park, University of Maryland, College park, Maryland, Yehuda-Zada, Y., Ghelman, M., Tsai, P., Thompson, A. K., Pritchard, K., Ziegler, J. B., Ibberson, R. M., Majkrzak, C. F., and Maliszewskyj, N. C. Wed . "{sup 6}LiF:ZnS(Ag) Neutrons Scintillator Detector Configuration for Optimal Readout". United States.
@article{osti_22531441,
title = {{sup 6}LiF:ZnS(Ag) Neutrons Scintillator Detector Configuration for Optimal Readout},
author = {Osovizky, A. and Rotem Industries Ltd, Rotem Industrial Park and University of Maryland, College park, Maryland and Yehuda-Zada, Y. and Ghelman, M. and Tsai, P. and Thompson, A. K. and Pritchard, K. and Ziegler, J. B. and Ibberson, R. M. and Majkrzak, C. F. and Maliszewskyj, N. C.},
abstractNote = {A Chromatic Analysis Neutron Diffractometer Or Reflectometer (CANDOR) is under development at the NIST Center for Neutron Research (NCNR). The CANDOR neutron sensor will rely on scintillator material for detecting the neutrons scattered by the sample under test. It consists of {sup 6}LiF:ZnS(Ag) scintillator material into which wavelength shifting (WLS) fibers have been embedded. Solid state photo-sensors (silicon photomultipliers) coupled to the WLS fibers are used to detect the light produced by the neutron capture event ({sup 6}Li (n,α) {sup 3}H reaction) and ionization of the ZnS(Ag). This detector configuration has the potential to accomplish the CANDOR performance requirements for efficiency of 90% for 5 A (3.35 meV) neutrons with high gamma rejection (10{sup 7}) along with compact design, affordable cost and materials availability. However this novel design includes challenges for precise neutron detection. The recognizing of the neutron signature versus the noise event produce by gamma event cannot be easy overcome by pulse height discrimination obstacle as can be achieved with {sup 3}He gas tube. Furthermore the selection of silicon photomultipliers (SiPM) as the light sensor maintains the obstacle of dark noise that does not exist when a photomultiplier tube is coupled to the scintillator. A proper selection of SiPM should focus on increasing the output signal and reducing the dark noise in order to optimize the detection sensitivity and to provide a clean signal pulse shape discrimination. The main parameters for evaluation are: - Quantum Efficiency (QE) - matching the SiPM peak QE with the peak transmission wavelength emission of the WLS. - Recovery time - a short recovery time is preferred to minimize the pulse width beyond the intrinsic decay time of the scintillator crystal (improves the gamma rejection based output pulse shape (time)). - Diode dimensions -The dark noise is proportional to the diode active area while the signal is provided by the WLS fibers; therefore the diode area should ideally be only minimally larger than fiber bundle area. - Low dark noise - it is desirable to minimize the dark noise during the pulse integration period so as to minimize the background for pulse shape discrimination. - Photon Detection Efficiency - it is desirable to increase the SiPM PDE in order to enhance light collection. This will increase the likelihood of detecting neutron events with lower light production and will present a cleaner raw signal for pulse shape discrimination. We will present the SiPM optimization process and studies of dark noise and gamma and neutron sensitivity as a function of bias voltage and operating temperature that have enabled us to optimize the detector sensitivity and gamma rejection. The gamma rejection performance goal requires to overcome the challenge of discriminating between the light signature accepted by neutron event to the one received by the noise. In addition there is a huge variation between the number of light photons that reaching the WLS fibers for different neutron events caused by the heavy ions energy losses prior to ionizing the ZnS(Ag) and the high light attenuation of the scintillation mixture. This variation in the light signal along with the long decay time of the ZnS(Ag) (tens of microseconds) can cause double counting of the same neutron event in the case of high light output signature or preventing the detection of low sequential light output signature neutron event. We will presents the algorithm developed for {sup 6}LiF:ZnS(Ag) sensor readout and the results achieved by an off-line analysis by Matlab software code that successfully achieved both the high gamma rejection with a sensitive and accurate neutron event detection. (authors)},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2015},
month = {7}
}

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