Organic Scintillation Detectors Research Articles

Validation of the FLUKA code to simulate response functions of organic liquid scintillator for high‐energy neutrons

In this research, the FLUKA code was employed to calculate the response functions of the BC501A organic scintillation detector for energies ranging from 25 to 800 MeV. Using the AUXSCORE, EVENTBIN and TCQUENCH cards, the response function of the BC501A organic scintillation detector to mono-energetic neutrons in the energy range of 25–800 MeV was computed. The comparison confirms that the simulation results obtained from the FLUKA code show a promising agreement with the results obtained from experiments, other codes, and the analytical method.

Characterization of diamond and organic scintillation detectors utilizing radiation sources for continuous plasma operation.

This paper provides a comprehensive study of neutron calibration methodologies, specifically highlighting the capabilities for n-γ discrimination in diamond and EJ-309, and stilbene scintillation detectors. The calibration process detailed in this study includes pulse height analysis and pulse shape discrimination, relying on the analysis of charge deposition resulting from both γ and neutron interactions. Utilizing 60Co and 252Cf radiation sources, the energy spectra of these sources are obtained. The characterized detectors were used in ST40 experiments and allowed acquiring neutron signal during a plasma shot with good agreement among diamond and scintillation detectors. Then, the diamond detector was cross-calibrated against indium activation foils placed at the same location in proximity to the ST40 during plasma shots: both detectors measured a neutron flux of ≈106 cm-2 s-1 at ≈1 m distance from the tokamak center, and the discrepancy between the diamond detector and the activation foils is ≈25%.

Neutron spectroscopy of plutonium using a handheld detection system

The ability to distinguish multiple forms of plutonium from one another, such as oxide and metal, is paramount in areas of nuclear nonproliferation and international safeguards. In its metal form, plutonium can be readily used in a nuclear weapon, while oxide forms are associated with nuclear reactor fuel. Oxide-based plutonium forms emit neutrons with an energy spectrum that is significantly different from the fission neutrons that are emitted from plutonium metal. Organic scintillation detectors output pulses that are proportional to the neutron energy deposited, and therefore present a means of distinguishing these plutonium forms based on their energy spectra. In this work, metal and oxide forms of plutonium were measured using a handheld detection system based on an organic glass scintillator. Monte Carlo modeling of these experiments was performed to provide insight into the origin of the features in the observed light output spectra. Through analysis of multiple regions of these spectra, in a matter of minutes we were able to unambiguously discriminate oxide and metal plutonium forms from one another and from a plutonium-beryllium neutron source, which was considered for comparison because these sources are commonly used in industrial applications. The ability to discriminate weapons-usable material from nuclear reactor fuel has applications in nuclear treaty verification and safeguards.

Response of a high-pressure 4He scintillation detector to nuclear recoils up to 9 MeV

Helium-4-based scintillation detector technology is emerging as a strong alternative to pulse-shape discrimination-capable organic scintillators for fast neutron detection and spectroscopy, particularly in extreme gamma-ray environments. The 4He detector is intrinsically insensitive to gamma radiation, as it has a relatively low cross-section for gamma-ray interactions, and the stopping power of electrons in the 4He medium is low compared to that of 4He recoil nuclei. Consequently, gamma rays can be discriminated by simple energy deposition thresholding instead of the more complex pulse shape analysis. The energy resolution of 4He scintillation detectors has not yet been well-characterized over a broad range of energy depositions, which limits the ability to deconvolve the source spectra. In this work, an experiment was performed to characterize the response of an Arktis S670 4He detector to nuclear recoils up to 9 MeV. The 4He detector was positioned in the center of a semicircular array of organic scintillation detectors operated in coincidence. Deuterium–deuterium and deuterium–tritium neutron generators provided monoenergetic neutrons, yielding geometrically constrained nuclear recoils ranging from 0.0925 to 8.87 MeV. The detector response provides evidence for scintillation linearity beyond the previously reported energy range. The measured response was used to develop an energy resolution function applicable to this energy range for use in high-fidelity detector simulations needed by future applications.

Development of indigenous pulse-shape discrimination algorithm for organic scintillation detectors

In this study, we present the development of an indigenous pulse shape discrimination (PSD) algorithm grounded in tail area and total area analysis, effectively obviating the necessity for specialized programmable hardware. Pulse data was collected utilizing a BC501 detector paired with a Pu-Be source and digitized in oscilloscope mode during experiments conducted at IIT-Kanpur. The algorithm developed in this work encompasses essential functions such as pulse normalization, shaping, peak identification and removal, and threshold determination. Notably, the algorithm offers the capability to derive neutron and γ-ray counts, generate scatter plots, and calculate the figure-of-Merit (FoM). It is essential to emphasize that the development of this indigenous Tail-to-Total Area (TtoT) PSD algorithm was a direct response to the unavailability of dedicated hardware for PSD in the experiment conducted at IIT-Kanpur. The introduction of the TtoT algorithm played a pivotal role in enabling offline PSD analysis at IIT-Kanpur, effectively overcoming infrastructure limitations. Importantly, the efficacy of our proposed algorithm was tested by applying it to pulse data from a distinct source-detector arrangement featuring a BC501A detector and an Cf-252 source. This comparative analysis also included the Charge Integration (CI) method and was conducted at IIT-Roorkee. The results obtained from our algorithm and the CI method exhibited a strong concurrence concerning the identification of neutrons and γ-rays, along with FoM metrics.

Wavelet-based digital pulse-shape method for discrimination between neutron and gamma-rays with organic scintillation detectors

Organic scintillator detectors are central instruments in many applications involving fast neutrons. Many organic scintillator detectors exhibit pulse-shape discrimination (PSD) properties and are widely used to discriminate between neutron events and background gamma rays. PSD methods have been traditionally implemented using analog electronic circuits; however, in recent years, digital techniques have proven to outperform analog methods in areas such as count rate capability. Many digital PSD algorithms with various levels of achievement have been proposed, and those based on the wavelet transform of digitized scintillation pulses have shown great promise for operation at high event rates, where the pulse pile-up effect limits the performance of PSD methods. However, the proposed wavelet-based PSD methods involve intricate calculations that limit their practical use. In this work, we describe a modified version of the wavelet-based PSD methods that offers significant simplification of the PSD process while still producing excellent PSD performance. The method employs the Haar wavelet transform, which is the simplest available wavelet function and is easily implemented on digital hardware, such as field-programmable gate arrays (FPGA). We describe the details of the method, and different aspects of its performance are experimentally demonstrated using an experimental setup comprising a NE213 liquid scintillation detector. A figure-of-merit (FOM) of 1.47 ± 0.07 is achieved with an energy threshold of 500 keVee (electron equivalent energy). An excellent FOM value (1.32) is achieved with a short pulse processing window of only 26 ns, indicating the resilience of the method against the pulse pile-up effect.

A comparison of the neutron detection efficiency and response characteristics of two pixelated PSD-capable organic scintillator detectors with different photo-detection readout methods

We characterize the performance of two pixelated neutron detectors: a PMT-based array that utilizes Anger logic for pixel identification and a SiPM-based array that employs individual pixel readout. The SiPM-based array offers improved performance over the previously developed PMT-based detector both in terms of uniformity and neutron detection efficiency. Each detector array uses PSD-capable plastic scintillator as a detection medium. We describe the calibration and neutron efficiency measurement of both detectors using a 137Cs source for energy calibration and a 252Cf source for calibration of the neutron response. We find that the intrinsic neutron detection efficiency of the SiPM-based array is (30.2 ± 0.9)%, which is almost twice that of the PMT-based array, which we measure to be (16.9 ± 0.1)%.

Characterisation of neutron fields at the n-lab, a fast neutron facility at the University of Cape Town

The n-lab is a fast neutron facility based in the Department of Physics, University of Cape Town, offering collimated neutron beams produced by an MP 320 deuterium–tritium sealed tube neutron generator, and a 220 GBq americium–beryllium radioisotopic source. Characterisations of the spatial and energy distributions of the fast neutron beams were performed using an EJ-301 organic liquid scintillator detector and digital data acquisition system. Neutron energy spectra were obtained through unfolding analyses with MAXED, and a Monte Carlo approach to the propagation of uncertainties was implemented. Measurements of fluence and neutron emission rates were determined through the neutron activation of copper foils and subsequently used to validate the scaling of the unfolded neutron energy spectra.

Multiplicity counting using organic scintillators to distinguish neutron sources: An advanced teaching laboratory

In this advanced instructional laboratory, students explore complex detection systems and nondestructive assay techniques used in the field of nuclear physics. After setting up and calibrating a neutron detection system, students carry out timing and energy deposition analyses of radiation signals. Through the timing of prompt fission neutron signals, multiplicity counting is used to carry out a special nuclear material (SNM) nondestructive assay. Our experimental setup is comprised of eight trans-stilbene organic scintillation detectors in a well-counter configuration, and measurements are taken on a spontaneous fission source as well as two (α,n) sources. By comparing each source's measured multiplicity distribution, the resulting measurements of the (α,n) sources can be distinguished from that of the spontaneous fission source. Such comparisons prevent the spoofing, i.e., intentional imitation, of a fission source by an (α,n) neutron source. This instructional laboratory is designed for nuclear engineering and physics students interested in organic scintillators, neutron sources, and nonproliferation radiation measurement techniques.

Deep neural network-based pulse shape discrimination of neutrons and $$\gamma $$-rays in organic scintillation detectors

Deep neural network-based pulse shape discrimination of neutrons and $$\gamma $$-rays in organic scintillation detectors

Pulse height estimation and pulse shape discrimination in pile-up neutron and gamma ray signals from an organic scintillation detector using multi-task learning

We developed a multi-tasking deep learning model for simultaneous pulse height estimation and pulse shape discrimination for pile-up n/γ signals. Compared with single-tasking models, our model showed better spectral correction performance with higher recall for neutrons. Further, it achieved more stable neutron counting with less signal loss and a lower error rate in the predicted gamma ray spectra. Our model can be applied to a dual radiation scintillation detector to discriminatively reconstruct each radiation spectrum for radioisotope identification and quantitative analysis.

Generalized method for the optimization of pulse shape discrimination parameters

Organic scintillators exhibit fast timing, high detection efficiency for fast neutrons and pulse shape discrimination (PSD) capability. PSD is essential in mixed radiation fields, where different types of radiation need to be detected and discriminated. In neutron measurements for nuclear security and non proliferation effective PSD is crucial, because a weak neutron signature needs to be detected in the presence of a strong gamma-ray background. The most commonly used deterministic PSD technique is charge integration (CI). This method requires the optimization of specific parameters to obtain the best gamma-neutron separation. These parameters depend on the scintillating material and light readout device and typically require a lengthy optimization process and a calibration reference measurement with a mixed source. In this paper, we propose a new method based on the scintillation fluorescence physics that enables to find the optimum PSD integration gates using only a gamma-ray emitter. We demonstrate our method using three organic scintillation detectors: deuterated trans-stilbene, small-molecule organic glass, and EJ-309. In all the investigated cases, our method allowed finding the optimum PSD CI parameters without the need of iterative optimization.

Pulse shape discrimination using a convolutional neural network for organic liquid scintillator signals

A convolutional neural network (CNN) architecture is developed to improve the pulse shape discrimination (PSD) power of the gadolinium-loaded organic liquid scintillation detector to reduce the fast neutron background in the inverse beta decay candidate events of the NEOS-II data. A power spectrum of an event is constructed using a fast Fourier transform of the time domain raw waveforms and put into CNN. An early data set is evaluated by CNN after it is trained using low energy β and α events. The signal-to-background ratio averaged over 1–10 MeV visible energy range is enhanced by more than 20% in the result of the CNN method compared to that of an existing conventional PSD method, and the improvement is even higher in the low energy region.

Fabrication of a Liquid Scintillator based on 7-Diethylamino-4-Methylcoumarin for Radiation Detection.

Organic liquid scintillation detectors are widely used to measure the presence of radiation. With these devices, there are advantages in that they are easy to manufacture, large in size, and have a short fluorescence decay time. However, they are not suitable for gamma spectroscopy because they are composed of a low-atomic-number material. In this regard, alternative materials for the secondary solute used in basic organic liquid scintillators have been investigated, and the applicability of alternative materials, the detection characteristics, and neutron/gamma identification tests were all assessed. 7-Diethylamino-4-methylcoumarin (DMC), selected as an alternative material, is a benzopyrone derivative in the form of colorless crystals with high fluorescence, a high quantum yield in the visible region, and excellent light stability. In addition, it has a large Stokes shift, and solubility in a solvent is good. Through an analysis in this study, it was found that the absorption wavelength range of DMC coincides with the emission wavelength range of PPO, which is the primary solute used with DMC. Finally, it was confirmed that the optimal concentration of DMC was 0.08 wt%. As a result of performing gamma and neutron measurement tests using a DMC-based liquid scintillator, it was found to perform well (FOM = 1.42) compared to a commercial liquid scintillator, BC-501A.

Energy measurement of 241Am-[formula omitted]Be neutrons by tagged neutron time-of-flight

Neutron energy spectrum of a 241Am-9Be source was measured in the energy range of 0.3 to ∼ 6.5 MeV using γ-ray tagged neutron time-of-flight method. BC501A type organic liquid scintillator detector was used at a flight path of 175 cm to detect neutrons with good energy resolution. The de-excitation γ-ray emitted in coincidence with neutrons was detected using a fast BaF2 detector. The measured data has been compared with the ISO 8529-2 standard neutron reference spectrum and found good agreement in the overlapping energy region. Present measurement applied efficiency correction to the data and extended up to 0.3 MeV in the lower energy region compared to earlier reported measurement using similar technique.

Reconstruction of fast neutron direction in segmented organic detectors using deep learning

A method for reconstructing the direction of a fast neutron source using a segmented organic scintillator-based detector and deep learning model is proposed and analyzed. The model is based on recurrent neural network, which can be trained by a sequence of data obtained from an event recorded in the detector and suitably pre-processed. The performance of deep learning-based model is compared with the conventional double-scatter detection algorithm in reconstructing the direction of a fast neutron source. With the deep learning model, the uncertainty in source direction of 0.301 rad is achieved with 100 neutron detection events in a segmented cubic organic scintillator detector with a side length of 46 mm. To reconstruct the source direction with the same angular resolution as the double-scatter algorithm, the deep learning method requires 75% fewer events. Application of this method could augment the operation of segmented detectors operated in the neutron scatter camera configuration for applications such as special nuclear material detection.

Potential for a precision measurement of solar pp neutrinos in the Serappis experiment

The Serappis (SEarch for RAre PP-neutrinos In Scintillator) project aims at a precision measurement of the flux of solar pp neutrinos on the few-percent level. Such a measurement will be a relevant contribution to the study of solar neutrino oscillation parameters and a sensitive test of the equilibrium between solar energy output in neutrinos and electromagnetic radiation (solar luminosity constraint). The concept of Serappis relies on a small organic liquid scintillator detector (sim 20 m^3) with excellent energy resolution (sim 2.5% at 1 MeV), low internal background and sufficient shielding from surrounding radioactivity. This can be achieved by a minor upgrade of the OSIRIS facility at the site of the JUNO neutrino experiment in southern China. To go substantially beyond current accuracy levels for the pp flux, an organic scintillator with ultra-low {^{14}hbox {C}} levels (below 10^{-18}) is required. The existing OSIRIS detector and JUNO infrastructure will be instrumental in identifying suitable scintillator materials, offering a unique chance for a low-budget high-precision measurement of a fundamental property of our Sun that will be otherwise hard to access.

Energy calibration of EJ-301 scintillation detector using unfolding methods for fast neutron measurement

We simulated a 2′′×2′′ EJ-301 organic liquid scintillation detector in the GEANT4 framework to obtain its response to standard gamma and neutron sources. The resolution scale and Birks’ constant for the EJ-301 scintillator have been estimated by comparing the simulation with experimental data. We calibrated the detector for fast neutron measurements with the help of an Am–Be source using two unfolding methods: RooUnfold and Gravel unfold. The neutron spectra obtained from both unfolding methods are similar to the Am–Be ISO (International Organization for Standardization) spectrum. The calibrated detector can be used in an underground site to understand the neutron background in rare event search experiments.

A Method to Improve Gamma Energy Resolution of BC-420 Type Organic Scintillation Detector

A Method to Improve Gamma Energy Resolution of BC-420 Type Organic Scintillation Detector

Improving Pulse Shape Discrimination in Organic Scintillation Detectors by Understanding Underlying Data Structure

Various machine learning techniques have been implemented to assist in neutron-gamma discrimination with great success compared to traditional methods. Despite this, the fundamental structure of a pulse shape as it relates to machine learning has not yet been explored in detail, and the optimal number of pulse vector features needed for training is still unknown. In this study, support vector machines (SVMs) using linear, radial basis, and exponential kernel functions are fitted on data of two different forms: waveforms that partially cover the original pulses and principal components extracted from those pulses. The described methods correctly classified 98.02% for neutrons and 97.84% for gamma rays. The efficiency of the SVM was improved by extracting principal components from the waveforms. That is, fewer features were needed to discriminate between neutrons and gamma rays without negatively impacting the classification accuracy. This study also shows that utilizing a nonlinear kernel significantly reduces the number of features required to reach high classification accuracy. SVMs that did this could make accurate classifications 97% of the time with data that had fewer than 50 features.