Pulse Shape Discrimination Capability Research Articles

Light Output Function and Pulse-Shape Discrimination Capability of p-Terphenyl Organic Scintillator in Wide Neutron Energy Range of 1.1 to 19 MeV

In this work, we studied the light-output properties, efficiency function, as well as the pulse-shape discrimination (PSD) capability of p-Terphenyl scintillator. The selected solid cylindrical scintillation detector has a thickness of 45 mm and a diameter of 45 mm. Recently presented studies of light-output functions have only been measured for low-neutron energies. Our motivation has been to determine the light output function for p-Terphenyl scintillator more accurately over a wider neutron energy range. The measurements have been carried out with mono-energetic neutron beams in the wide energy range from 1.1 to 19 MeV. The neutron–gamma spectrometric system which we developed has been used for the measurement. The input analog signal from the detector was digitized with a fast 12-bits analog to digital converter with a sampling frequency of 1 GHz. Measured data from the detector are processed into the gamma and neutron spectra. The accurate light output function for the p-Therphenyl scintillator has been calculated. The pulse-shape discrimination capability, as well as the detection efficiency, of a p-Terphenyl scintillator are lower in comparison with a NE-213 equivalent detector.

Performance of large-scale [formula omitted]Li-doped pulse-shape discriminating plastic scintillators

A 6Li-doped plastic scintillator with pulse-shape discrimination capabilities, commercially identified as EJ-299-50, has been developed and produced at the kilogram-scale. A total of 44 kg-scale bars of dimensions 5.5 cm x 5.5 cm x 50 cm of this material have been characterized. Optical properties like light output and effective attenuation length have been found to be comparable to 6Li-doped liquid scintillators. The scintillator EJ-299-50 shows good neutron detection capabilities with an effective efficiency for capture on 6Li of approximately 85%. Stability tests performed on two formulation variations showed no intrinsic degradation in the material or optical properties during several months of observations.

Characterization of EJ-276D plastic scintillator and its comparison with EJ-299-33A and BC-501A

A characteristic study of the new generation EJ-276D plastic scintillator detector, measuring 5 inches in diameter and 5 inches in length, was conducted. This study compared it with the earlier EJ-299-33A plastic scintillator and the BC-501A liquid scintillator. Key characteristics such as pulse height response, pulse shape discrimination, efficiency, and time resolution were measured and compared for each detector of the same dimensions. The results show that the performance of EJ-276D is superior to EJ-299-33A in every aspect. It exhibits comparable efficiency but lower pulse shape discrimination capabilities compared to the BC-501A liquid scintillator. Notably, the stability of the EJ-276D over time was also studied and found to be satisfactory.

Development of a bi-solvent liquid scintillator with slow light emission

One of the most promising approaches for the next generation of neutrino experiments is the realization of large hybrid Cherenkov/scintillation detectors made possible by recent innovations in photodetection technology and liquid scintillator chemistry. The development of a potentially suitable future detector liquid with particularly slow light emission is discussed in the present publication. This cocktail is compared with respect to its fundamental characteristics (scintillation efficiency, transparency, and time profile of light emission) with liquid scintillators currently used in large-scale neutrino detectors. In addition, the optimization of the admixture of wavelength shifters for a scintillator with particularly high light emission is presented. Furthermore, the pulse-shape discrimination capabilities of the novel medium was studied using a pulsed particle accelerator driven neutron source. Beyond that, purification methods based on column chromatography and fractional vacuum distillation for the co-solvent DIN (Diisopropylnaphthalene) are discussed.

Optimization of fast output from SiPM array for pulse shape discrimination techniques at high counting rates

Plastic scintillators with pulse shape discrimination (PSD) capability, when combined with silicon photo-multipliers (SiPMs), enable the development of compact neutron detectors with lower power consumption and insensitivity to magnetic fields. However, the SiPM array has a significantly large pulse width of the output signal, which leads to discrimination difficulties at high counting rates. There are two outputs of a SiPM array: a standard output for energy measurement and a fast output for timing measurement. The pulse width of the standard output signal is in the range of hundreds nanoseconds, while the pulse width of the other one is in the range of tens nanoseconds. Fast output signals have traditionally been considered suitably for fast timing, however utilizing them for PSD has been little explored. In our previous work, we successfully implemented PSD by using fast output signals from a SiPM. Despite the obvious negative overshoot in fast signals, we achieved PSD of fast signals by using longer sampling times. However, this approach was still limited at high counting rates. This study proposes a compensation network for fast output signals, which is composed of a compensation unit consisting of a resistor and a capacitor. This design effectively compensates the overshoot of the fast output and shortens the pulse width from 60 ns to 44 ns. Additionally, it highlights the frequency amplitude differences between the neutron and gamma signals from fast output in the high-frequency component, thus improving the PSD capability of the fast output.

Enhancement of alpha/beta ratio in NaI:Tl,6Li neutron-gamma scintillators by rare earth co-doping

NaI:Tl,6Li bulk crystals are regarded as promising neutron-gamma (n-γ) scintillators because of low production cost and superior n-γ pulse shape discrimination (PSD) performance. In this work, some rare earth elements (Gd, Y, Lu and Sc) co-doped NaI:Tl,6Li single crystals were grown by the multi-ampoule Bridgman method. It was found that the rare earth co-doping significantly improves the pulse height discrimination (PHD) capability of NaI:Tl,6Li with high alpha/beta (α/β) ratio, approaching to 100%. The optimal α/β ratios achieved for Gd, Y, Lu and Sc co-doped NaI:Tl,6Li are 0.85, 0.93, 0.95, and 0.83, respectively. Electron equivalent energy per neutron interaction is above 3.96 MeV and can be as high as 4.54 MeV, close to the Q value of 4.78 MeV for 6Li(n, α)3H interaction. Moreover, the rare earth co-doped NaI:Tl,6Li crystals still maintain the superior PSD capability with figure of merit (FoM) in the range of 2.1–3.3. These results highlight the great potential of rare-earth co-doped NaI:Tl,6Li crystals serving as high-performance n-γ scintillators.

Experimental characterization of discrimination capabilities of EJ-276 and EJ-276G read by SiPM by pulse-shape analysis techniques

This work aims at the investigation of the Pulse Shape Discrimination (PSD) capabilities of two very compact detection systems composed of a 3x3x3 cm3 EJ 276 and a 3x3x3 cm3 EJ 276G (the latter green shifted version) plastic scintillators, both coupled to Silicon Photomultiplier (SiPM). The studied systems are supposed to be the basic elementary cell of a new multi-detector for simultaneous detection of neutrons and light charged particles called NArCoS (Neutron Array for Correlation Studies) having both high angular and energy resolution. In this perspective, the results of the experimental qualification of two prototypes with gamma and alpha radioactive sources and in beam tests are reported, in order to characterize the optimum choice for the new device.

Neutron detection in mixed short-pulsed fields with intense photon flashes for LINAC-based active interrogation applications

High-energy photon interrogation has established itself as a valuable tool for detecting special nuclear materials and characterizing nuclear waste. Previous research predominantly uses around 9-MV linear electron accelerators (LINACs) as photon sources and limited exploration has been conducted on the use of organic scintillators to determine the energy deposited in the detector and to separate photon and neutron radiation, crucial when the photon interrogation is based on the measurement of the neutron emission. The challenge arises from the intense photon flux typically produced by electron accelerators, resulting in issues such as pulse pile-up, detector saturation, and a suboptimal signal-to-background ratio. This study aims to extend the applicability of the conventional Active Photon Interrogation (API) techniques by introducing a novel method enabling the detection, in addition to nuclear materials, of light elements—specifically nitrogen, oxygen, and carbon—known to be present in conventional explosives, narcotics, and chemical weapons. The approach relies on active photon interrogation at high energies above 12 MeV, coupled with photoneutron spectrometry. Using a 22-MV electron LINAC, pulse shape discrimination with an organic liquid scintillator demonstrated promising performance. Our results highlight that the conventional pulse shape discrimination capabilities and rapid time-scale operation of organic scintillators enable the detection of fast neutrons from (γ,Xn) reactions, even in a mixed short-pulsed field of photon and neutron radiation with intense photon flashes. This exploration of the initial experimental aspects of photoneutron detection induced by high-energy photons establishes a foundation for a promising new method for the detection of illicit materials.

Pure CaF2 crystal for fast neutron detection

Pure CaF2 crystals have been widely used for optical functional crystals due to their good optical properties, mechanical properties, and chemical stability. This study discovered the crystal's pulse shape discrimination (PSD), proving it a promising scintillator for fast neutron detection via the 40Ca neutron capture reaction. Luminescence emission spectra were studied by X-ray luminescence measurements. The maximum emission peak was observed between 250 and 300 nm, corresponding to self-trap exciton emission. The crystal response to gamma, alpha, and neutron were studied under 137Cs, 241Am, and 252Cf radiation sources, respectively. The difference in gamma and alpha decay times enabled the PSD capability of pure CaF2. Large neutron reaction cross-sections, PSD capability, and good chemical stability make pure CaF2 crystal candidates for fast neutron beam monitoring detectors. Moreover, the crystal can be used for 40Ca(n,p)40K and 40Ca(n,α)37Ag neutron capture cross-section study.

Pulse-shape discrimination capability of organic composite scintillators with different grain size

Pulse-shape discrimination capability of organic composite scintillators with different grain size

Scintillation properties of lithium-6 salicylate-loaded liquid scintillators.

The limited availability of conventional 3He proportional counters provides impetus for developing novel neutron detectors. As a candidate, lithium-6-loaded liquid scintillators with neutron/gamma pulse shape discrimination (n-γ PSD) capabilities have been developed. However, the trade-off relationship between the 6Li-loading amount and scintillation light yield is a significant problem. This is because 6Li-loading involves the addition of non-luminescent materials, which cause non-radiative relaxation of the excited states. Therefore, aiming to reduce non-radiative relaxation, we chose lithium-6 salicylate (6LiSal), which shows fluorescence in the visible light region, as a chemical for 6Li-loading. In this study, we analyzed the photoluminescence/scintillation properties based on the Förster resonance energy transfer and investigated the optimal content for obtaining a high light yield. By maximizing the sequential energy transfer from the solvent (toluene) to the phosphor (POPOP), a high light yield 6Li-loaded liquid scintillator (4220 photons per MeV under gamma-ray irradiation) with a 6Li concentration of approximately 0.1 wt% was developed. Thermal neutron events were successfully detected with a light yield of 3970 photons per neutron, which is more than three times higher than those of other organic scintillators. In addition, focusing on the triplet-triplet annihilation process and further optimizing the component for the n-γ PSD, the thermal neutron and gamma-ray events were successfully separated. The developed high light yield 6Li-loaded liquid scintillators show n-γ PSD capabilities and can be promising candidates as alternative detectors to the 3He proportional counter.

Characterization of organic glass scintillator bars and their potential for a hybrid neutron/gamma ray imaging system for proton radiotherapy range verification

For accurate and simultaneous imaging of fast neutrons (FNs) and prompt gamma rays (PGs) produced during proton therapy, the selection of a highly performant detector material is crucial. In this work, a promising candidate material known as organic glass scintillator (OGS) is characterized for this task. To this end, a precisely-timed source of neutrons and Bremsstrahlung radiation produced by the nELBE facility was used to study the light output and neutron/gamma ray pulse shape discrimination (PSD) properties of a 1 × 1 × 20 cm3 OGS bar with double-sided readout. Furthermore, the energy, timing, and depth-of-interaction (DOI) resolutions of 1 × 1 × 10 cm3 and 1 × 1 × 20 cm3 OGS and EJ-200 bars were characterized with radioactive sources. For electron-equivalent energies above 0.5 MeVee, OGS was found to have excellent PSD capabilities (figure-of-merit above 1.27), energy resolution (below 12%), coincident time resolution (below 500 ps), and DOI resolution (below 10 mm). This work establishes the data analysis methods required for hybrid FN/PG imaging using OGS, and demonstrates the materials' excellent performance for this application.

Proton-induced radiation damage in Cs2LiYCl6:Ce scintillator

Cs2LiYCl6:Ce crystal scintillator (CLYC:Ce) has garnered significant attention for its applications in both neutron detection and gamma-ray spectroscopy. This is due to its excellent pulse shape discrimination (PSD) capabilities, which allow for distinguishing between neutrons and gamma rays. Recently, there has been interest in utilizing CLYC:Ce in high-dose environments, making it crucial to understand the effects of radiation damage on its performance. In this work, we aim to examine the impact of radiation damage on the scintillation performance of CLYC:Ce under 100 MeV proton beam. To minimize systematic uncertainty, the change in light output of CLYC:Ce was measured at different accumulated doses using the same experimental setup. The pulse shape discrimination for thermal neutrons was assessed before and after irradiation. Additionally, the decay time of gamma-ray and thermal neutron-induced pulses was analyzed at various accumulated doses. The results of these analyses provide support for little degradation of pulse shape discrimination even with the high proton dose. Furthermore, the study considered and discussed the scintillation recovery of CLYC:Ce over a month. Despite the substantial damage induced by high-energy protons, the results demonstrate that CLYC:Ce remains a promising scintillator for thermal neutron detection.

Impact of temperature on light yield and pulse shape discrimination of polysiloxane-based organic scintillators formulated with commercial resins

This work investigates how increased temperature affects neutron/γ discrimination and light yield (LY) in several different polysiloxane-based scintillators doped with either 9,9-dimethyl-2-phenylflourene (PhF) or 2,5-diphenyloxazole (PPO) as a primary fluorophore and 9,9-dimethyl-2,7-di((E)-styryl) fluorene (SFS) as the secondary fluorophore. The polysiloxane matrices were prepared from the commercial resins Wacker Lumisil 579 or Shin-Etsu KER-6000. Control scintillators were prepared from poly(vinyltoluene) (PVT), the industry standard matrix, as a reference point for LY and pulse shape discrimination (PSD) measurements. Samples with PhF and PPO dopant concentrations of 1 wt% and 5 wt% in the polysiloxanes and 3 wt% and 5 wt% in the PVT samples were tested at 20 °C, 35 °C, and 50 °C. In the polysiloxane samples, the KER-6000 resin outperformed the Wacker 579 and PhF proved to be a better dopant than PPO in both LY and PSD capabilities. Polysiloxane scintillators showed slight decreases in LY and increases in neutron/γ discrimination at increased temperatures, while PVT scintillators showed a similar LY decrease with little to no improvement in neutron/γ discrimination at increased temperatures. Overall, polysiloxane scintillators may not require recalibration in applications where temperatures increase up to 50 °C.

Development of Directional 14 MeV-Fusion Neutron Detector Using Liquid-Scintillator-Filled Capillaries

Triton burnup studies have been performed in fusion experimental devices to evaluate the confinement performance of 3.5 MeV alpha particles. For this purpose, the generation rate of deuterium-tritium (D-T)-born 14 MeV neutrons has been measured using a scintillating fiber detector. The directionality of this detector provides excellent selectivity for 14 MeV neutrons; however, the lack of a pulse–shape discrimination (PSD) capability limits high-energy gamma-ray reduction. In this study, we developed a new 14 MeV neutron detector with directionality that can discriminate neutrons and gamma rays based on the PSD technique by filling capillaries with a liquid scintillator. The performance of this detector was evaluated at the FNL (Tohoku University, Japan) and OKTAVIAN (Osaka University, Japan). The detector response was modeled using the particle and heavy ion transport code system (PHITS). The experimental and simulation results demonstrated that the detector has a directional response to fast neutrons and excellent PSD capability.

Pulse shape discrimination and spectral performance of an inverted coaxial point contact HPGe detector with sub-pF capacitance

The inverted coaxial point contact high purity germanium (ICPC HPGe) detector exhibits the advantages of large volume, low depletion voltage, small capacitance, and excellent pulse shape discrimination (PSD) capability. An ICPC detector prototype with 0.9 pF capacitance was successfully fabricated and tested in this study using two different front-end electronics. The detector weighted approximately 1.5 kg and the depletion voltage was only 1800 V. The optimized operating voltage was found to be 2500 V and the leakage current was 7 pA. The detector was first connected to a homemade JFET based front-end with a pulsed reset design to minimize parallel noise. An energy resolution of 1.72 keV (full width at half maximum) was achieved at 1332 keV, demonstrating the good charge collection efficiency of the detector. An RC feedback front-end circuit was employed to test the PSD properties using a 228Th source. The PSD capability is similar to that of typical broad energy or point contact HPGe detectors, but is notably improved when the charge trapping is corrected using the drift time.

Effects of alkali ions on luminescence and scintillation performance of Ce3+ doped phosphate glasses for radiation detection

The luminescence and scintillation properties of Ce3+ doped alkali phosphate glasses 56P2O5:8Gd2O3:5Al2O3:1CeBr3:30XCl (PGAC:X, X = Li/Na/K/Rb/Cs) were studied for their potential applications in gamma and alpha detection. In the Fourier Transform Infrared Spectroscopy (FTIR), X-ray Luminescence (XRL), Photoluminescence (PL), and transmittance spectra, the red shift was found and explained by the concept of optical basicity. Broad Ce3+ emission and energy transfer from Gd3+ to Ce3+ were observed in XRL and PL measurements. Scintillation performance was studied by irradiating the samples under 137Cs gamma and 241Am alpha sources. The fast, intermediate, and slow decay components under gamma and alpha excitation were found around 30, 200 and 3000 ns, respectively. The decay time increased slightly from PGAC:Li to PGAC:Cs, indicating the less effective transition from Gd3+ to Ce3+. The alpha decay time was longer than the gamma decay time, revealing the Pulse Shape Discrimination (PSD) capability of the glasses for particle identification. The XRL intensity reduced significantly from PGAC:Li to PGAC:Cs samples did not reflect the scintillation tendency. By successfully detecting gamma and alpha scintillation signals, the scintillation performance of all samples was found to be similar. In general, all samples can be used for gamma and alpha detection. Using Rb+ or Cs+ ions is favorable in terms of high density and light yield, while Li+ ions enhance the transmittance and homogeneity. Furthermore, a correlation between P–O–H groups within the glass matrix and scintillation performance was also observed.

Development of neutron detection systems at the NDPS of RAON

The Nuclear Data Production System (NDPS) at RAON has been built to produce nuclear data generated by the reactions induced by neutrons of tens of MeV. For the neutron Time-Of-Flight (TOF) measurement, neutron monitoring detectors based on a gas-filled Parallel Plate Avalanche Counter (PPAC) and a MICRO-MEsh-GASeous (MICROMEGAS) detector have been developed by the Rare Isotope Science Project (RISP) and Sungkyunkwan University (SKKU). These detectors have a neutron converter with a thin 232Th layer, which produces fission products due to fast neutrons. The PPAC achieved a 1 ns FWHM time resolution in a test with an 241Am α source and also showed good performance when tested with fast neutrons generated by a 45 MeV proton beam through the 9Be(p, n)9B reaction. Additionally, EJ-301, liquid scintillation detectors are assembled for the measurement of neutron flux with pulse shape discrimination capability. Slow charge signals as well as fast timing signals from the detectors will be processed for particle identification by a data acquisition (DAQ) system, located at a separate control room through 30 m long cables. Development of the detection system and the test results will be reported together with the on-site assembly status.

Pulse shape analysis of LiI:Tl crystal scintillators

The LiI:Tl crystal is a candidate for thermal neutron measurements and rare event searches due to the advantage of the lithium and iodide isotopes in its composition. This study shows the pulse shape discrimination (PSD) capability of thermal neutron irradiation. Particle discrimination is essential for improving neutron measurement and rare event searches to reduce unwanted backgrounds. To investigate the pulse-shape characteristics of LiI:Tl crystals with different radiations, digital analysis of pulse shape has been considered. The raw pulses were fitted with a suitable pulse form. The fitted pulses were studied in both the time and frequency domains which improve the Figure-of-Merit over the charge comparison methods. Our results show the change of PSD for LiI:Tl crystals with different Thallium concentrations. The surface effect is discussed, and other related scintillation characteristics were also studied.

Performance evaluation of pulse shape discrimination capable organic scintillators for space applications

Scintillators with pulse-shape discrimination (PSD) capability are of great interest to many fields in the scientific community. The ability to discern a gamma ray from a neutron using PSD varies between different types of scintillator materials and dopants. A new generation of organic scintillator materials with PSD capability were studied to determine their radiation hardness to neutron and gamma-ray radiation. The PSD capability, average pulse shapes, and light output of four types of organic scintillator were characterized before and after neutron and gamma-ray irradiation. The main goal of this investigation is to study the effects of long-term irradiation that may be experienced in space applications on the light output and particle discriminating capabilities of each material. EJ-270, EJ-276, organic glass, and Stilbene were tested. Damage due to neutron irradiation (displacement damage) was not observed in any of the scintillators up to 2.56×1011 n/cm2, except for Stilbene which showed a small (12%) decrease in light output. All scintillators presented some light output reduction after gamma-ray irradiation (total ionizing dose), with reductions of 17% (EJ-276 and OGS), 32% (EJ-270), and 42% (Stilbene) observed immediately after 100 kRad.