Pulse Shape Discrimination Properties Research Articles

Evaluation of radon absorption and detection properties of a plastic scintillator developed for PSD measurements

In the last decade, significant progress has been made in the development of plastic scintillators (PS) with effective neutron/gamma pulse shape discrimination (PSD). In this study, we investigate a plastic scintillator with remarkable neutron/gamma PSD properties for radon detection and alpha/beta PSD. The PS has outstanding alpha-/beta- PSD, energy resolution, and aging stability. It exhibits radon absorption properties with a diffusion length of 0.224(23) mm and a partition coefficient of 10.6(11) at 20(1) °C. We show how the absorption of radon can enhance studies on the alpha/beta PSD and energy resolution of plastic scintillators. Additionally, we introduce an improved peak shape model for the approximation of the PS’s alpha-particle spectrum of 222Rn and its short-lived decay products.

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.

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.

6Li-loaded liquid scintillators produced by direct dissolution of compounds in diisopropylnaphthalene (DIPN)

The paper describes preparation of 6Li-loaded liquid scintillators by methods involving direct dissolution of 6Li salts in the commercial diisopropylnaphthalene (DIPN) solvent, without the formation of water-in-oil emulsions. Methods include incorporation of 6Li that, unlike previously reported formulations, does not require additions of water or a strong acid such as hydrochloric acid (HCl). Results of the conducted experiments show that dissolution of aromatic and aliphatic 6Li salts in DIPN can be easily achieved at 0.1%–0.3% by weight of atomic 6Li, using small additions of waterless surfactants, or mild carboxylic acids. An alternative way suggests incorporation of 6Li as a part of a surfactant molecule that can be dissolved in DIPN without any solubilizing additions. Proposed methods enable preparation of efficient 6Li-loaded liquid scintillators that, at a large scale of 50 cm, exhibit good pulse shape discrimination (PSD) properties combined with up to 107% of light output and up to 115% of the attenuation length measured relative to standard undoped EJ-309 liquid scintillator.

Measurement of light output response in scintillator based neutron detectors using quasi-monoenergetic neutrons

Conventional liquid scintillator (BC501A) and pulse shape discrimination capable plastic scintillator (EJ-299-33A) based detector of dimension; 5 inch diameter and 5 inch long, have been used to study pulse height response for quasi-monoenergetic neutrons of energy in the range 3 to 15 MeV generated using 7Li(p,n)7Be reaction. Scintillation light output of plastic scintillator having pulse shape discrimination property is found to be 75% of the liquid scintillator at neutron energy (maximum recoil proton energy) of 3 MeV which improves with the increase in energy. Functional dependence of the scintillation light output in terms of recoil protons energy has been determined for the liquid and the plastic scintillator detectors for neutron energy in the range 3 to 15 MeV. This functional dependences were used in the Geant4 simulation to calculate the pulse height responses at several neutron energies.

Comparative scintillation performance of EJ-309, EJ-276, and a novel organic glass

An organic glass scintillator developed by Sandia National Laboratories was characterized in terms of its light output and pulse shape discrimination (PSD) properties and compared to commercial liquid (EJ-309) and plastic (EJ-276) organic scintillators. The electron light output was determined through relative comparison of the 137Cs Compton edge location. The proton light yield was measured using a double time-of-flight technique at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Using a tunable broad-spectrum neutron source and an array of pulse-shape-discriminating observation scintillators, a continuous measurement of the proton light yield was performed for EJ-309 (200 keV–3.2 MeV), EJ-276 (170 keV–4.9 MeV), and the organic glass (50 keV–20 MeV) . Finally, the PSD properties of the organic glass, EJ-309, and EJ-276 were evaluated using an AmBe source and compared via a figure-of-merit metric. The organic glass exhibited a higher electron light output than both EJ-309 and EJ-276. Its proton light yield and PSD performance were comparable to EJ-309 and superior to that of EJ-276. With these performance characteristics, the organic glass scintillator is well poised to replace current state-of-the-art PSD-capable scintillators in a range of fast neutron detection applications.

Simulated X-Ray Radiographic Performance of a Bismuth-Loaded PVT Array

Recent material advancements in organic plastic scintillators enable marked increases in material detection efficiency, light yield, and pulse shape discrimination properties. These advances may resolve significant capability gaps for low-cost, portable, and durable dual-particle imaging (DPI) systems for nuclear safety, security, and safeguard purposes. One such material, a 21% bismuth-loaded polyvinyl toluene (BiPVT), is computationally evaluated as a small, pixelated radiographic array using Monte Carlo N-Particle (MCNP) and Zemax OpticStudio, and it is compared to identical evaluations of EJ-200 and EJ-256 arrays. MCNP software enables estimates of particle interaction and energy deposition, while OpticStudio computes optical light transport within each material. Computational estimates of spatial resolution and relative light collection at 370 kVp are found to agree with experimental results for both EJ-200 and EJ-256 arrays, thereby validating predictions of the same for the BiPVT array. As such, for equivalent exposures at 370 kVp, a BiPVT array may provide $\sim 20\times $ the light collection expected from EJ-200 and $\sim 10\times $ that expected from EJ-256. Similar comparisons of estimated light collection are also computed at 150 and 270 kVp, and these results suggest that BiPVT will provide significantly improved performance over EJ-200 and EJ-256 across all energies practical for portable X-ray radiography.

PROSPECT – A precision reactor oscillation and spectrum experiment

PROSPECT is a reactor antineutrino experiment whose primary goals are to search for short-baseline neutrino oscillations and perform a precise measurement of the [Formula: see text]U reactor antineutrino energy spectrum. Since March 2018, PROSPECT has operated a 4 ton antineutrino detector less than 10 m from the 85 MW High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory. Operating in this environment with tight space constraints and limited overburden to attenuate cosmic ray backgrounds is a significant technical challenge. The PROSPECT detector design uses efficient optical segmentation and a 6Li-doped liquid scintillator with good light yield and pulse-shape discrimination properties to achieve excellent energy reconstruction and background rejection in a compact, space efficient system. Initial results from PROSPECT have demonstrated the ability to detect 100 s of antineutrino events per day with good signal-to-background in this aboveground location and perform precise measurements of the HFIR antineutrino energy spectrum.

The Effect of Codoping on Pulse-Shape Discrimination Properties of Gd3Ga3Al2O12:Ce Single Crystals

In this article, we have extended our study on the effect of codopants on the scintillation properties of Ce-doped Gd3Ga3 Al2O12(GGAG:Ce) single crystals by investigating their pulse-shape discrimination (PSD) abilities. The GGAG:Ce crystals were grown with boron and calcium codopants using the Czochralski technique. The codoping was found to have substantial effects on the PSD ability of these scintillators. Observable difference in the pulse shapes for alpha and gamma radiations in the B-codoped GGAG:Ce scintillators exhibited the highest PSD, while those with Ca codoping showed no discrimination among the studied samples despite having a significant effect on the scintillation kinetics and a strong quenching of the light yield by alpha radiations that resulted in a minimum $\alpha / \gamma $ ratio. A correlation of the PSD properties with the defect structure of these single crystals has been made by using optically stimulated luminescence (OSL) for the first time. OSL studies with infrared, blue, and green light provided an insight into the role of defect centers in the relaxation mechanism of the scintillation kinetics of the GGAG:Ce crystals, which subsequently affects their ability to discriminate different kinds of radiation.

Plastic scintillators based on thermally activated delayed fluorescence dyes

Abstract Thermally activated delayed fluorescence (TADF) dyes are a class of luminescent organic compounds capable of the conversion of triplet to singlet excited states for increased photon emission efficiency, and these classes of dyes have recently attracted a great deal of attention for their potential use in highly efficient organic light emitting diodes (OLEDs). For organic scintillators utilizing conventional fluorescent dyes, triplet excited states generated from energy deposition of the incident particle’s energy can be converted to singlets via triplet–triplet annihilation, which leads to the delayed pulse tail characteristic of organic scintillators, but is not overall a particularly efficient process for triplet to singlet conversion. In this work, we investigated the applicability of the use of TADF dyes in organic scintillators, in particular for their capability for triplet to singlet conversion, and how these unique properties impact the overall scintillation photophysics. In particular, the prospects of using TADF dyes as a means for increased light yield as well as for efficient pulse shape discrimination (PSD) properties are directly addressed. In doing do, we explored the prominent effect that the dye’s singlet–triplet splitting energy ( Δ E ST ) – a parameter fundamental to the realization of efficient TADF processes – has on determining these properties, and our findings suggest that TADF dyes could eventually enable an entirely new generation of high performance organic scintillators.

A CsI(Tl) detector array for the measurement of light charged particles in heavy-ion reactions

An array of eight CsI(Tl) detectors has been set up to measure the light charged particles in nuclear reactions using heavy ions from the Pelletron Linac Facility, Mumbai. The energy response of CsI(Tl) detector to α-particles from 5 to 40 MeV is measured using radioactive sources and the 12C(12C, α) reaction populating discrete states in 20Ne. The energy non-linearity and the count rate effect on the pulse shape discrimination property have also been measured and observed the deterioration of pulse shape discrimination with higher count rate.

Neutron and gamma-ray pulse shape discrimination of LiAlO2 and LiGaO2 crystals

In this research, we found that some undoped crystals (LiAlO2 and LiGaO2) show pulse shape discrimination (PSD) capabilities, and we report some basic scintillation and PSD properties of these crystals. These two crystals show scintillation spectrum with an emission peak at around 330 nm, and the spectral shapes of the two were identical. The scintillation decay curves consist of decay components on the order of micro-second for both the crystals under X-ray excitation, and the decay times were specify values. When we irradiated the samples with neutrons from 252Cf and γ-rays from 60Co, we found that decays vary for signals generated by neutron and γ-rays. A two-dimensional histogram of pulse heights of the slow and fast components for LiAlO2 and LiGaO2 clearly showed neutron and γ-ray events separated in the two-dimensional histogram indicating material’s capacity for PSD.

Performance of custom designed inverted coaxial HPGe detectors for Gerda and Legend

Five new HPGe detectors enriched in 76 G e have been characterized in the framework of the on-going upgrade of the Gerda experiment. These new detectors have been designed such as to combine excellent spectral and pulse shape discrimination properties, together with an increase of a factor ∼ 2 in mass with respect to the detectors currently used in Gerda . Excellent spectral performances have been confirmed (energy resolution ∼ 0 . 1 % for all prototypes), though an unexpected feature in the Pulse Shape Discrimination parameter has been observed, and has to be further investigated.

Detailed investigation on the possibility of using EJ-299-33A plastic scintillator for fast neutron spectroscopy in large scale experiments

Detailed characterization of the newly available plastic scintillator (EJ-299-33A) having the pulse shape discrimination (PSD) property has been carried out in case of a large-sized detector (5 in.×5 in.). The pulse height response of the scintillator for nearly mono-energetic neutrons has been reported in case of neutron energies En =3, 6 and 9 MeV. Important properties (figure-of-merit (FOM), time resolution, detection efficiency) of the detector has been compared with a commonly used liquid organic scintillator based detector of the same size coupled to the same PMT for uniformity in comparison. The results show that the plastic scintillator detector has about 12% better time resolution. However, the FOM and detection efficiency were found to be lower than that of the liquid scintillator detector by 40 - 50% and ∼25%, respectively. The possibility of using the new plastic scintillator in large-scale nuclear physics experiments has been pointed out.

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 shape discrimination of plastic scintillator EJ 299-33 with radioactive sources

The present study has been carried out in order to investigate about the possibility of using EJ 299-33 scintillator in a multi-detector array to detect neutrons along with light charged particles. In a reaction induced by stable and exotic heavy-ions beams, where copious production of neutrons and other light charged particles occurs, discrimination with low identification threshold of these particles are of great importance. In view of this, EJ 299-33 scintillator having dimension of 3 cm × 3 cm × 3 cm backed by a photomultiplier tube was tested and used under vacuum to detect neutrons, gamma-rays and alpha particles emitted by radioactive sources. Anode pulses from the photomultiplier tube were digitized through GET electronics, recorded and stored in a data acquisition system for the purpose of an off-line analysis. The measurements, under vacuum and low background conditions, show good pulse shape discrimination properties characterized by low identification threshold for neutrons, gamma-rays and alpha particles. The Figures of Merit for neutron-gamma and alpha particles-gamma discriminations have been evaluated together with the energy resolution for gamma-ray and alpha particles.

Correlated fission data measurements with DANCE and NEUANCE

To enhance the capabilities of the DANCE array, a new detector array NEUANCE was developed to enable simultaneous measurements of prompt fission neutrons and γ rays. NEUANCE was designed and constructed using 21 stilbene organic scintillator crystals. It was installed in the central cavity of the DANCE array. Signals from the 160 BaF2 detectors of DANCE and the 21 detectors of NEUANCE were merged into a newly designed high-density high-throughput data acquisition system. The excellent pulse shape discrimination properties of stilbene enabled detection of neutrons with energy thresholds as low as 30–40 keVee. A fission reaction tagging method was developed using a NEUANCE γ-ray or neutron signal. The probability of detecting a neutron from the spontaneous fission of 252Cf using NEUANCE is ∼47%. New correlated data for prompt fission neutrons and prompt fission γ rays were obtained for 252Cf using this high detection efficiency experimental setup. Average properties of prompt fission neutron emission as a function of prompt fission γ-ray quantities were also obtained, suggesting that neutron and γ-ray emission in fission are correlated.

10B enriched plastic scintillators for application in thermal neutron detection

We report here on the synthesis and characterization of a novel 10B enriched aromatic molecule that can be incorporated into common poly(vinyltoluene) (PVT) based plastic scintillators to achieve enhanced thermal neutron detection. Starting from relatively inexpensive 10B enriched boric acid, we have prepared 4,4,5,5-tetramethyl-2-phenyl-1,3,2-dioxaborolane (MBB) in three high yield steps. MBB is soluble and compatible with PVT based formulations and results in stable plastic scintillators. Chemical synthesis, solubility limit in PVT, and the physical properties of the dopant were explored. The relevant response properties of the resulting scintillators when exposed to neutron and gamma radiation, including light yield and pulse shape discrimination properties were measured and analyzed.

Electronics for the STEREO experiment

The STEREO experiment, aiming to probe short baseline neutrino oscillations by precisely measuring reactor anti-neutrino spectrum, is currently under installation. It is located at short distance from the compact research reactor core of the Institut Laue-Langevin, Grenoble, France. Dedicated electronics, hosted in a single µTCA crate, were designed for this experiment. In this article, the electronics requirements, architecture and the performances achieved are described. It is shown how intrinsic Pulse Shape Discrimination properties of the liquid scintillator are preserved and how custom adaptable logic is used to improve the muon veto efficiency.

Pulse shape discrimination properties of Gd3Ga3Al2O12:Ce,B single crystal in comparison with CsI:Tl

Single crystals of Gd3Ga3Al2O12:Ce,B and CsI:Tl were grown by Czochralski and Bridgman techniques, respectively. While both the crystals exhibited similar emission at about 550nm, their scintillation decay times showed significantly different characteristics. The average scintillation decay time of Gd3Ga3Al2O12:Ce,B crystal was found to be about 284ns for alpha excitation compared to 108ns measured for a gamma source. On the other hand in CsI:Tl crystals, the alpha excitation resulted in a lower average decay time of 600ns compared to 1200ns with gamma excitation. Their pulse shape discrimination (PSD) for gamma and alpha radiations were studied by coupling the scintillators with photomultiplier tube or SiPM and employing an advanced digitizer as well as a conventional zero-crossing setup. In spite of having a poor α/γ light yield ratio, the PSD figure of merit and the difference of zero-crossing time in Gd3Ga3Al2O12:Ce,B crystals were found to be superior in comparison to CsI:Tl crystals.