Pulse Shape Discrimination Technique Research Articles

Real-Time Implementation of the Neutron/Gamma Discrimination in an FPGA-Based DAQ MTCA Platform Using a Convolutional Neural Network

These days, research on the classification of neutron/gamma waveforms in scintillators using pulse shape discrimination (PSD) techniques is a highly studied topic. Numerous methods have been explored to optimize this classification, with some of the most recent research being focused on machine learning techniques with excellent results. These approaches are mainly based on the use of 1-D convolutional neural networks (CNNs). In this field, field-programmable gate arrays (FPGAs) with high-sampling rate analog to digital converters (ADCs) have been used to perform this classification in real-time. In this work, we select a potential architecture and implement it with the help of the IntelFPGA OpenCL SDK environment. A shorter and C-like development of OpenCL enables a more straightforward modification and optimization of the network architecture. The main goal of this work is the evaluation of the needed resources and the obtained performance to prototype a complete solution in the FPGA. The FPGA design is generated as if it was connected to an ADC module streaming the data samples with the help of a Board Support Package developed for an IntelFPGA ARRIA10 available in an Advanced Mezzanine Card (AMC) module in an Micro Telecommunications Computing Architecture (MTCA.4) platform. The prototyped solution has been integrated into Experimental Physics and Industrial Control System (EPICS) using the nominal device support (NDS) model currently being developed by ITER.

A novel technique for real-time ion identification and energy measurement for in situ space instrumentation

The AGILE (Advanced enerGetic Ion eLectron tElescope) project focuses on the development of a compact low-cost space-based instrument to measure the intensities of charged particles and ions in space. Using multiple layers of fast silicon sensors and custom front-end electronics, the instrument is designed for real-time particle identification of a large variety of elements from H to Fe and spanning energies from 1 to 100 MeV per nucleon. The robust method proposed in this work uses key defining features of electronic signals generated by charged particles (ions) traveling through silicon layers to reliably identify and characterize particles in situ. AGILE will use this real-time pulse shape discrimination technique for the first time in space based instrumentation.

Application of artificial neural network in neutron/gamma pulse shape discrimination for EJ301 scintillation detector

The scintilator detectors are sensitive to both neutron and gamma radiation. Therefore, right identification of the pulses which generated by neutrons or gamma ray from these detectors plays an important role in neutron measurement by using scintilator detector. In order to improve the ability to pulse shape discrimination (PSD), many PSD techniques have been studied, developed and applied. In this work, we use a basic configuration of a Fully connected Neural network (Fc- Net) where the number of elements of the network is minimum, and each element corresponds to identified specification of neutron or gamma pulses measured by using EJ-301 scintilator detector. The minimum of error principle has been applied for neuron network design; therefore, the accuracy of recognitions did not affect by this reduced network. The obtained results show that the identify accuracy of FcNet is higher than those of digital charge integration (DCI) method. Being tested using 60Co radioactive source, it is shown that, with the application of the FcNet, the accuracy of the gamma pulses discrimination acquires 98.60% in the energy region from 50 to 2000 keV electron equivalent energy (keVee), and 95.59% in the energy region from 50 to 150 keVee. In general, the obtained results indicate that the artificial neural network method can be applied to build neutron/gamma spectrometers with limited hardware.

Neutron response of the TLYC scintillator

The response of the recently developed Tl2LiYCl6(Ce) scintillator to neutrons was measured and the 35Cl(n,p) channel observed in the material for the first time. The scintillator was exposed to a 252Cf source mounted within a parallel-plate avalanche counter for fission-fragment coincident measurements. Proton- and t+α-like events are selected with the pulse-shape discrimination technique. Comparison of energy-deposition and time-of-flight allows the quenching of the different channels to be assessed. The 6Li(n,t)α channel is found to have its energy quenched to 37(1)% relative to γ-ray detection, while the proton energy deposition spectrum is quenched to 60(1)%.

Sorting fission from parasitic coincidences of neutrons and gamma rays in plastic scintillators using particle times of flight

This work addresses the use of plastic scintillators as an alternative to 3He detectors for radioactive waste drum characterization. The time response of scintillators is three orders of magnitude faster than that of gas proportional counters and they offer similar neutron detection efficiency at lower cost. However, they are sensitive to gamma rays and the commonly used Pulse Shape Discrimination technique is not possible with basic PVT scintillators. This paper reports on an innovative data processing technique allowing to extract spontaneous fission events from parasitic coincidences, such as those from the (α,n) reactions accompanied by correlated gamma rays or from pure gamma-ray sources emitting correlated radiations. The proposed approach makes advantage of differences in the pulse detection times recorded in measurements with the 252Cf, AmBe and 60Co sources. More precisely, a 2D histogram of time delays between the detected 2nd and 1st pulses, on the x-axis, and between the 3rd and 2nd pulses, on the y-axis, is found to allow for selection of a region of interest most relevant to spontaneous fission events.

Assessment of a polymeric composite as a radiation attenuator and a restoration mortar for cracking in biological shields

This work is dedicated to figuring out robust epoxy/magnetite/boron carbide (EP/Mag/B4C) composite for radiation attenuation at multiple applications related to nuclear installations, as well as restoration mortar for cracking developed in concrete biological shields. The mechanical properties (flexural, compressive, and impact strengths) and the physical properties (water absorption, porosity, and dry bulk density), each, have been performed to label the composite integrity for practical application. In practice, attenuation properties have been performed by using a collimated beam emitted from spontaneous fission 252Cf (100 μg) neutron source and neutron gamma spectrometer with stilbene scintillator. The pulse shape discrimination technique which would come of the zero cross over method was used to measure the fast neutron and gamma-ray spectra. Thermal neutron fluxes have been measured by using the thermal neutron detection system and the BF-3 detector. The attenuation parameters: precisely, macroscopic effective removal cross-sections ΣR (cm-1), macroscopic cross-sections Σ (cm-1), and total attenuation coefficients μ (cm-1) of fast and thermal neutrons and total gamma-rays respectively were evaluated using the attenuation relations. Also, the MCNP5 code and MERCSF-N program have been used to compute the parameters theoretically. When applicable, measured and calculated results were compared, and it tells us a comprehensive agreement.

Thermal neutron measurement by single crystal CVD diamond detector applied with the pulse shape discrimination during deuterium plasma experiment in LHD

Abstract The Pulse shape discrimination (PSD) technique for single crystal CVD diamond detector (SDD) was applied to the real-time thermal neutron measurement during the 3rd campaign of Deuterium-Deuterium (D-D) plasma experiment in the Large Helical Device (LHD). The PSD method is based upon the different shape of electrical pulses produced in diamond by gamma-ray (triangular-shaped pulse) and energetic ions (rectangular-shaped pulse), respectively. An improved PSD was developed which makes use of the full width at half maximum (FWHM) and the full width at 2/3 of the peak height (FW2/3 PH). These two parameters reflect the difference in the pulse shape produced by gamma-rays and energetic ions. The performance of this improved PSD technique was first tested irradiating the SDD by gamma-rays from 60Co and alphas from 241Am radiation sources, respectively. Then, using a 6LiF thermal neutron converter, a successful discrimination between gamma-rays and alpha particles and tritons generated by the 6Li(n,α)3H reaction induced by neutrons from 252Cf spontaneous fission neutron source was achieved. Thanks to this PSD processing technique, the thermal neutron detection efficiency increased about 1.7 times compared to previous measurements performed without the PSD technique. The real-time thermal neutron measurement by SDD with this enhanced PSD processing was also used during D-D plasma discharges in the Large Helical Device (LHD). It was found that both the time integrated counts and the time evolution count rate measured by the SDD reproduced well that of the fission chamber used as official LHD neutron monitor. The capability of the SDD detector using the PSD technique of precise real-time thermal neutron measurement in LHD was demonstrated.

Measurement of the Neutron Energy Spectra by Using Organic Scintillators at the Beam Dump of the 100-MeV Proton Linear Accelerator in the KOMAC

This paper presents the experimental results of neutron spectra measurements with organic scintillators at the copper beam dump of the 100-MeV proton linear accelerator in the Korea Multi-Purpose Accelerator Complex (KOMAC). For the measurement of the fast neutrons generated by the proton-copper nuclear reaction, two organic scintillators made of a stilbene crystal and liquid EJ-309 combined with photomultipliers and fast digitizers were utilized. Both detectors were installed inside radiation shielding structures facing the conical-shaped 100-MeV proton beam dump. The neutron transport was calculated using two Monte-Carlo codes, MCNP6 and GEANT4, with a proper physical model and a nuclear data library, along with the appropriate consideration of the detailed geometrical factors in the vicinity of the beam-dump and the neutron detectors. Each pulse signal measured in the detectors was analyzed to identify whether it was induced by a neutron or a gamma-ray in a mixed radiation field by using pulse shape discrimination technique. For operation of beam current of 5 mA and duty of 0.2%, the neutron yield was measured to be approximately 9.0E+10 n/s, which was 23% smaller than the numerically estimated value. In addition, both the measured and the estimated neutron energy spectra were compared.

Investigation of ASIC-based signal readout electronics for LEGEND-1000

LEGEND, the Large Enriched Germanium Experiment for Neutrinoless ββ Decay, is a ton-scale experimental program to search for neutrinoless double beta (0νββ) decay in the isotope 76Ge with an unprecedented sensitivity. Building on the success of the low-background 76Ge-based GERDA and \ extsc{Majorana Demonstrator} experiments, the LEGEND collaboration is targeting a signal discovery sensitivity beyond 1028 yr on the decay half-life with approximately 10 t⋅yr of exposure. Signal readout electronics in close proximity to the detectors plays a major role in maximizing the experiment's discovery sensitivity by reducing electronic noise and improving pulse shape analysis capabilities for the rejection of backgrounds. However, the proximity also poses unique challenges for the radiopurity of the electronics. Application-specific integrated circuit (ASIC) technology allows the implementation of the entire charge sensitive amplifier (CSA) into a single low-mass chip while improving the electronic noise and reducing the power consumption. In this work, we investigated the properties and electronic performance of a commercially available ASIC CSA, the XGLab CUBE preamplifier, together with a p-type point contact high-purity germanium detector. We show that low noise levels and excellent energy resolutions can be obtained with this readout. Moreover, we demonstrate the viability of pulse shape discrimination techniques for reducing background events.

Characterization of CLLBC Coupled to Silicon Photomultipliers

Cs2LiLaBr6- x Cl x :Ce (CLLBC) has high energy resolution for gamma detection and high sensitivity for neutron detection. It is one of the neutron-gamma dual-mode scintillators developed in recent years. This work studies the performance of an 18-mm CLLBC cube for gamma and neutron detection for temperatures between − 20 °C and 50 °C. In addition, the scintillator was coupled to the SensL J- and C-series silicon photomultipliers (SiPMs) for comparison. Throughout the temperature range, better energy resolution is observed for the scintillator coupled to the J-series SiPMs which can be attributed to the higher photon detection efficiency. For thermal neutron detection, the output of the detector was recorded by a waveform digitizer and analyzed offline on a computer. To distinguish neutrons from gammas, a pulse shape discrimination technique was utilized. A good separation between neutrons and gammas is observed for all the temperatures. However, separating neutrons from the intrinsic alphas is somewhat difficult at low temperatures. In spite of this, this 18-mm CLLBC cube is a high-performance scintillator and is suitable for deployment in radiation detectors for nuclear security and safeguards applications.

INVESTIGATION OF PULSE SHAPE NEUTRON-GAMMA DISCRIMINATION

The role of neutron beam investigation is significant not only for fundamental science but also for various fields of applied science. This work is dedicated to the formation of neutron beams using the external 18-MeV proton beam of IBA cyclotron C18/18 with a beam current of up to 100 µA. The facility is located at the A. Alikhanyan National Science Laboratory (Yerevan Physics Institute). The possibility to obtain thermal or epithermal neutron beams using the external proton beam of the cyclotron is studied using Geant4 simulations. In this case, a quasimonoenergetic neutron source 9Be (p, n)9B reaction is chosen. As a result of the simulations, the optimal thickness of the 9Be beryllium isotope target is determined. The induced neutron beam is accompanied by a gamma ray background. To decrease the number of accompanying gamma rays, the lead absorber is considered. As a method of separating neutrons from gamma rays, the pulse shape discrimination (PSD) technique is developed. This study shows the possibility of neutron-gamma PSD and its applicability using the EJ-299-33A plastic scintillator.

INVESTIGATION OF PULSE SHAPE NEUTRON-GAMMA DISCRIMINATION

The role of neutron beam investigation is significant not only for fundamental science but also for various fields of applied science. This work is dedicated to the formation of neutron beams using the external 18-MeV proton beam of IBA cyclotron C18/18 with a beam current of up to 100 µA. The facility is located at the A. Alikhanyan National Science Laboratory (Yerevan Physics Institute). The possibility to obtain thermal or epithermal neutron beams using the external proton beam of the cyclotron is studied using Geant4 simulations. In this case, a quasimonoenergetic neutron source 9Be (p, n)9B reaction is chosen. As a result of the simulations, the optimal thickness of the 9Be beryllium isotope target is determined. The induced neutron beam is accompanied by a gamma ray background. To decrease the number of accompanying gamma rays, the lead absorber is considered. As a method of separating neutrons from gamma rays, the pulse shape discrimination (PSD) technique is developed. This study shows the possibility of neutron-gamma PSD and its applicability using the EJ-299-33A plastic scintillator.

6LiF:ZnS(Ag) Neutron Detector Performance Optimized Using Waveform Recordings and ROC Curves.

We used Gaussian separation and receiver operating characteristic (ROC) curves to optimize the neutron sensitivity and gamma rejection of an ultra-thin 6LiF:ZnS(Ag)-scintillator-based neutron detector paired with a silicon photomultiplier (SiPM). We recorded the waveforms while operating the detector in a monochromatic cold neutron beam and in the presence of isotopic 137Cs and 60Co gamma sources. We used a two-window charge comparison (CC) pulse-shape discrimination (PSD) technique to distinguish the neutron capture events from other types of signals. By feeding the recorded waveforms through variants of this algorithm, it was possible to optimize the duration of the integration windows [(0-100 ns) for the prompt window and (100-2300 ns)] for the delayed window. We then computed the detector's ROC curve from waveform recordings and compared that with the experimental performance. We also used this procedure to compare a series of detector configurations to select the optimal bias voltage for the SiPM photosensor.

Organic scintillator-based alpha/beta detector for radiological decontamination

Abstract A detector that can distinguish alpha from beta particles is valuable for detecting alpha emitters from contamination at and around the Fukushima Daiichi Nuclear Power Plant (FDNPP), and other nuclear facility decontamination sites. We developed a prototype alpha/beta particle detector using a pulse shape discrimination (PSD) capable organic scintillator , a silicon photomultiplier, and a waveform digitizer. The charge integration PSD technique was used to separate alpha and beta particles. We compared the PSD figure of merit (FOM) values of two scintillators (EJ-299-33 and stilbene), and found that the stilbene ( FOM = 1 . 61 ) performance was superior to the EJ-299-33 ( FOM = 0 . 56 ) performance, measured using an 241 Am source (5.5 MeV alpha particle emission) and a 90 Sr source. Additionally, the stilbene showed good energy resolution (23.6 %FWHM for 5.5 MeV alpha particles). In the pulse height spectrum for the 90 Sr ∕ 90 Y source, the lower energy portion ( 90 Sr ) and the higher energy portion ( 90 Y ) could be separated. To demonstrate the detector’s separation ability, the 232 Th source was measured. The measurements demonstrated the alpha and beta particle separation, and alpha and beta spectra were obtained simultaneously, which was not possible when using commercial detectors such as a ZnS(Ag) scintillation detector.

The partial truncated icosahedron phoswich array for detection of low energy charged pions and light charged particles

The Partial Truncated Icosahedron (ParTI) phoswich array has been designed for the detection of low energy charged pions and other light charged particles for the study of pionic fusion reactions. The array consists of 15 plastic/CsI(Tl) phoswich detector units arranged in approximately one hemisphere of a truncated icosahedron geometry. The phoswich detectors’ particle identification capabilities have been characterized. A pulse shape discrimination technique has demonstrated isotopic identification for Z = 1 and Z = 2 particles and elemental identification up to at least Z = 3. Utilization of digital electronics allows for increased sensitivity in event triggering and independent verification of pion detection. A calibration technique for the array has also been developed.

A large area detector for thermal neutron flux measurements at the KamLAND site

A large area (0.5 m × 0.5 m) thermal neutron detector was developed based on 0.32 mm-thick 6LiF:ZnS(Ag) scintillator sheets. The detector was constructed for measurements of seasonal variations in low intensity thermal neutron flux at deep underground sites. The detector response to neutrons was studied using a low intensity 241Am/9Be(α,n) neutron source. The digital pulse shape discrimination technique was applied to separate neutron capture events from the background caused by traces of α-emitters from Uranium and Thorium decay chains in scintillator components. The thermal neutron detection efficiency was 0.368 ± 0.018 (0.155 ± 0.009) before (after) event selection based on the digital pulse shape discrimination method. The measured α-particle background event rate in the 6LiF:ZnS(Ag) scintillator was (4.88 ± 0.06(stat))×10−6α cm−2 s−1. As a test of detector performance we measured the thermal neutron flux at the KamLAND area of the Kamioka neutrino observatory and compared it with result of the neutron flux measurement carried out at the Super-Kamiokande site. The thermal neutron flux at KamLAND was (6.43 ± 0.50)×10−6 n cm−2 s−1 that included ∼10% contribution from neutrons with energies above 1 eV. During the detector construction we identified a source of high amplitude noise pulses generated by 5-inch R1250 photomultipliers manufactured by Hamamatsu Photonics K. K.

Study of fast neutron detector for COSINE-100 experiment

A monitoring system for fast neutrons is planned in the COSINE experiment, a dark matter experiment with NaI crystals. We pursued several R&D approaches for a neutron detector using a liquid scintillator (LS). A pulse shape discrimination (PSD) technique is used for the identification of neutron events and the PSD properties of two different LS were compared. A good separation power between neutrons and γ has been achieved for energies between 200 keVee to 1500 keVee. The combination of alumina adsorption, filtration, and water extraction is effective in purifying the LS, which leads to a reduction in the α contamination by 210Po of more than a factor of two. The measured activities of the internal α are 0.36±0.04 mBq/kg and 0.21±0.03 mBq/kg before and after purification, respectively.

Pulse discrimination with a Gaussian mixture model on an FPGA

A Gaussian Mixture Model (GMM) based machine learning algorithm has been applied to the problem of gamma/neutron pulse shape discrimination (PSD). The algorithm has been successfully implemented on a standard PC as well as a field programmable gate array (FPGA). Here we describe the GMM classifier and its implementation on these two different types of hardware. We compare the performance of the algorithm on these two platforms against each other, along with other standard techniques applied in PSD. Our results show that the FPGA-based GMM classifier outperforms the standard PSD techniques in terms of classification accuracy at low particle energy and executes more quickly than its CPU-based counterpart.

A remotely triggered fast neutron detection instrument based on a plastic organic scintillator.

A detector system for the characterization of radiation fields of both fast neutrons and γ rays is described comprising of a gated photomultiplier tube (PMT), an EJ299-33 solid organic scintillator detector, and an external trigger circuit. The objective of this development was to conceive a means by which the PMT in such a system can be actuated remotely during the high-intensity bursts of pulsed γ-ray contamination that can arise during active interrogation procedures. The system is used to detect neutrons and γ rays using established pulse-shape discrimination (PSD) techniques. The gating circuit enables the PMT to be switched off remotely. This is compatible with use during intense radiation transients to avoid saturation and the disruption of the operation of the PMT during the burst. Data are presented in the form of pulse-height spectra and PSD scatter plots for the system triggered with a strobed light source. These confirm that the gain of the system and the throughput for both triggered and un-triggered scenarios are as expected, given the duty cycle of the stimulating radiation. This demonstrates that the triggering function does not perturb the system response of the detector.

Mitigation of ^{42}Ar/^{42}K background for the GERDA Phase II experiment

Background coming from the ^{42}Ar decay chain is considered to be one of the most relevant for the Gerda experiment, which searches for the neutrinoless double beta decay of ^{76}Ge. The sensitivity strongly relies on the absence of background around the Q-value of the decay. Background coming from ^{42}K, a progeny of ^{42}Ar, can contribute to that background via electrons from the continuous spectrum with an endpoint at 3.5 MeV. Research and development on the suppression methods targeting this source of background were performed at the low-background test facility LArGe . It was demonstrated that by reducing ^{42}K ion collection on the surfaces of the broad energy germanium detectors in combination with pulse shape discrimination techniques and an argon scintillation veto, it is possible to suppress ^{42}K background by three orders of magnitude. This is sufficient for Phase II of the Gerda experiment.