Gamma-ray Discrimination Research Articles

Influence of a cross-linker agent on mechanical and other properties of polysiloxane based scintillators

Polysiloxane scintillators (PSS) are of great interest due to their neutron and gamma-ray (n/γ) discrimination capability and excellent radiation hardness. However, one major drawback is their low mechanical hardness. To address this issue, we present a cross-linking agent, 1,3-diethenyl-1,3-dimethyl-1,3-diphenyldisiloxane (DS), incorporated into PSS to study its effects on various physical properties. It was found that the enhanced inter-chain entanglement of covalently bonded polymer chains by the DS cross-linker significantly improved the mechanical hardness and optical properties. Gravimetric analysis (TGA) indicated a slightl improvement in stability during thermal degradation. This cross-linker at 0-17 wt% concentrations has also slightly positive impact on the PSD performance as demonstrated by measurements of pulse shape discrimination (PSD) using a 238Pu-Be neutron source. The improved cross-linking density helped prevent both the generation of free molecule radicals and diffusion of fluorophore dyes. Consequently, the cross-linked samples remained transparent with no dye precipitation, even after 12 months of storage.

Boron-10 Doped Polysiloxanes as Matrix Materials for Application in the Simultaneous Detection and Discrimination of Gamma Rays and Fast and Thermal Neutrons

Boron-10 Doped Polysiloxanes as Matrix Materials for Application in the Simultaneous Detection and Discrimination of Gamma Rays and Fast and Thermal Neutrons

Discrimination of neutrons and gamma-rays in plastic scintillator based on spiking cortical model

In this study, a spiking cortical model (SCM) based n-γ discrimination method is proposed. The SCM-based algorithm is compared with three other methods, namely: (i) the pulse-coupled neural network (PCNN), (ii) the charge comparison, and (iii) the zero-crossing. The objective evaluation criteria used for the comparison are the FoM-value and the time consumption of discrimination. Experimental results demonstrated that our proposed method outperforms the other methods significantly with the highest FoM-value. Specifically, the proposed method exhibits a 34.81% improvement compared with the PCNN, a 50.29% improvement compared with the charge comparison, and a 110.02% improvement compared with the zero-crossing. Additionally, the proposed method features the second-fastest discrimination time, where it is 75.67% faster than the PCNN, 70.65% faster than the charge comparison and 38.4% slower than the zero-crossing. Our study also discusses the role and change pattern of each parameter of the SCM to guide the selection process. It concludes that the SCM's outstanding ability to recognize the dynamic information in the pulse signal, improved accuracy when compared to the PCNN, and better computational complexity enables the SCM to exhibit excellent n-γ discrimination performance while consuming less time.

Anti-noise performance of the pulse coupled neural network applied in discrimination of neutron and gamma-ray

In this study, the anti-noise performance of a pulse-coupled neural network (PCNN) was investigated in the neutron and gamma-ray (n−gamma) discrimination field. The experiments were conducted in two groups. In the first group, radiation pulse signals were pre-processed using a Fourier filter to reduce the original noise in the signals, whereas in the second group, the original noise was left untouched to simulate an extremely high-noise scenario. For each part, artificial Gaussian noise with different intensity levels was added to the signals prior to the discrimination process. In the aforementioned conditions, the performance of the PCNN was evaluated and compared with five other commonly used methods of n−gamma discrimination: (1) zero crossing, (2) charge comparison, (3) vector projection, (4) falling edge percentage slope, and (5) frequency gradient analysis. The experimental results showed that the PCNN method significantly outperforms other methods with outstanding mathrm{FoM}-value at all noise levels. Furthermore, the fluctuations in mathrm{FoM}-value of PCNN were significantly better than those obtained via other methods at most noise levels and only slightly worse than those obtained via the charge comparison and zero-crossing methods under extreme noise conditions. Additionally, the changing patterns and fluctuations of the mathrm{FoM}-value were evaluated under different noise conditions. Hence, based on the results, the parameter selection strategy of the PCNN was presented. In conclusion, the PCNN method is suitable for use in high-noise application scenarios for n−gamma discrimination because of its stability and remarkable discrimination performance. It does not rely on strict parameter settings and can realize satisfactory performance over a wide parameter range.

Pulse-Shape Discrimination of SiPM Array-Coupled CLYC Detector Using Convolutional Neural Network

Cs2LiYCl6: Ce3+ (CLYC) is a dual-mode gamma-neutron scintillator with a medium gamma-ray resolution and pulse-shape discrimination (PSD) capability. The PSD performance of CLYC is greatly weakened when coupled with silicon photomultipliers (SiPMs) because of SiPMs’ low detection efficiency for the ultrafast Core-Valence-Luminescence (CVL) component under gamma excitation. In our previous work, the PSD Figure-of-Merit (FoM) value was optimized to 2.45 at the gamma-equivalent energy region of the thermal neutron by using the charge comparison method. However, this value was reduced to 1.37 at the lower gamma-equivalent energy region of more than 325 keV, and neutrons were difficult to distinguish from gamma rays. Hence, new algorithms should be studied to improve the PSD performance at low gamma-equivalent energy regions. Convolutional Neural Networks (CNNs) have excellent image recognition capabilities, and thus, neutron and gamma-ray waveforms can be discriminated by their characteristics through a known training set. In this study, neutron and gamma-ray waveforms were measured with a 137Cs source and moderated 252Cf source via an SiPM array-coupled CLYC detector and divided into two groups: training and PSD testing. The CNN training set comprised 137Cs characteristic gamma-ray waveforms and thermal neutron waveforms that were discriminated by the charge comparison method from the training group. A CNN with two convolution-pooling layers was designed to accomplish PSD with the test group. The PSD FoM value of the CNN method was calculated to be 37.20 at the gamma-equivalent energy region of more than 325 keV. This result was much higher than that of the charge comparison method, indicating that neutrons and gamma rays could be better distinguished with the CNN method, especially at low gamma-equivalent energy regions.

Formula omitted]: A new variable for γ/h discrimination in large gamma-ray ground arrays

In this letter, a new strategy to enhance the discrimination of high energy gamma rays from the huge charged cosmic rays background in large cosmic rays ground arrays is presented. This strategy is based on the introduction of a new simple variable, Pγhα, which combines the probability of tagging muons and/or very energetic particles in each single array station. The discrimination power of this new variable, particularly important for and above multi-TeV energies, is illustrated for a few specific examples in the case of a hypothetical water Cherenkov detector cosmic ray array, both in the case of low and high particle stations occupancy. The results are very encouraging and hopefully will be demonstrated in the present and future gamma-ray Observatories.

Discrimination of neutrons and gamma rays in plastic scintillator based on pulse-coupled neural network

Discrimination of neutrons and gamma rays in plastic scintillator based on pulse-coupled neural network

Discrimination of neutrons and gamma-rays in plastic scintillator based on falling-edge percentage slope method

With the development of neutron detection technology, the demand for real-time and fast neutron gamma discrimination has become of increasing importance. In this study, neutron and gamma pulse signals measured by an EJ299-33A plastic scintillator detector were analyzed via Matlab off-line. This study compares the effects of seven fast neutron and gamma (n/γ) discrimination methods; (i) charge comparison method, (ii) time-domain oriented method, (iii) amplitude oriented method, (iv) pulse time–amplitude two types of width method, (v) angle difference method, (vi) falling-edge numerical integral method, and, lastly, (vii) falling-edge percentage slope method proposed in this study. We verified that filtering and amplitude normalization improve the discrimination quality but consume much time that accounts for 99.6% of the total discrimination time. The proposed method was compared with other six methods in two aspects: (i) the figure of merit (FoM), (ii) the discrimination time. The FoM value and time consumption of the falling-edge percentage slope method with amplitude normalization are 1.26 and 0.0621s, respectively, while an unnormalized FoM value is 1.02. Experimental results showed that compared with all aforementioned methods, the FOM value of our proposed method is the second high followed the charge comparison method, retaining a short discrimination time which is only half of that of the charge comparison method. This relatively short time consuming is on account of its low volume of data storage and calculation. Generally, the falling-edge percentage slope method has a good discrimination performance while consumes little time, which is capable to be implemented on real-time discrimination applications.

K-Nearest Neighbors regression for the discrimination of gamma rays and neutrons in organic scintillators

Certain organic scintillators, such as EJ-299 and stilbene, have the ability to distinguish gamma rays and neutrons through the process of pulse shape discrimination (PSD). This work introduces the novel application of a K-Nearest Neighbor (KNN) regressor to improve PSD performance, and applies it to six combinations of photosensors and organic scintillators, with a focus on silicon photomultiplier-based detectors. The method allows for direct comparison against conventional PSD methods by way of a typical PSD Figure of Merit (FOM), while avoiding the uncertainties associated with classification-based machine learning algorithms to achieve an assessment free from predetermined label bias. Tests were conducted to validate the proposed PSD regression method, and parameters such as input features and the number of nearest neighbors used were investigated to maximize the method’s performance. FOM values over a light output range of 200–700 keVee are shown, with improvements ranging from approximately 60% to over 200% when compared to conventional PSD methods. Finally, studies were performed to determine the lower bound of light output at which gamma ray and neutron groupings are still statistically separable. Results indicate that this light output bound can be lowered across all six tested detector-assembly combinations with the proposed KNN regression method when compared to the conventional PSD methods.

Optimization and characterization of a silicon photomultiplier-based ZnS(Ag) proton recoil fast neutron detector for nuclear fuel performance monitoring at TREAT

The restart of the Transient Reactor Test Facility (TREAT) at Idaho National Laboratory and consequent refurbishment of the Fuel Motion Monitoring System (FMMS), or Hodoscope, offers the opportunity to upgrade the detector system used for neutron imaging. Silicon photomultipliers (SiPMs) are a viable option for updating the Hodoscope to yield improved fuel monitoring capability. The Hodoscope uses ZnS(Ag) proton recoil scintillators (PRS) that provide good gamma-ray suppression and discrimination. Previous work showed that the Hamamatsu S13360-6075CS SiPM offers the best neutron detection and gamma-ray discrimination capability with the ZnS PRS. This work optimizes a SiPM-based detector and develops a PRS prototype for testing. Specifically, possible overvoltages for use are determined by confirming steady operation over extended measurement times. In addition, various SiPM-circuit implementations are tested to optimize the detector according to desired properties, and ultimately a PRS prototype is developed with modifiable components for versatile testing. Measurements of the neutron detection efficiency and gamma-ray rejection efficiency of SiPM-based PRS detectors and a reference PMT-based detector are also carried out. Neutron detection efficiency ranges between 1–2%, and detected gamma-ray rejection efficiency is on the order of 10−7. Use of a low-pass filter only or a low-pass filter and 50-ω shunt resistor is recommended for the SiPM-based detector, and both configurations demonstrate improved performance over the PMT-based detector.

Performance assessment of amplification and discrimination electronic devices for passive neutron measurements

The knowledge of the fissile material mass is a key challenge to enhance radioactive waste management and to ensure a high level of safety in nuclear industry. Data is analyzed according to the principles of the neutron measurement techniques. As proportional counters filled with 3He gas display high neutron detection efficiency and a good gamma-ray discrimination, they are the reference detector for passive neutron coincidence counting. A charge preamplifier or a current amplifier, depending on applications, collects the electric pulse produced by neutron interaction in the 3He gas and a threshold discriminator produces a logic pulse used for neutron counting. This paper describes the performance assessment of different commercially available electronics from Mirion Technologies, Precision Data Technology (PDT), Mesytec, as well as MONACO electronics originally developed by CEA LIST for fission chamber measurements in experimental reactors. Comparative passive neutron measurements are carried out with these electronics at CEA/DEN Nuclear Measurement Laboratory in Cadarache. Overall, PDT and Mesytec electronics show similar detection efficiency as the ACH-NA98 charge amplifier, which is commonly used in our laboratory for such applications. However, MONACO electronics have a lower detection efficiency, similar to Mirion 7820 current amplifier used in specific high-count rate applications. An optimisation of MONACO settings would probably be necessary to adapt to 3He counters instead of fission chambers.

Digital pulse processing algorithm for neutron and gamma rays discrimination

This paper presents a proposed algorithm for discriminating neutron and gamma radiation events. In the proposed algorithm, discriminating features are extracted from the input radiation event. These features are extracted using charge integration, matched filtering, and Discrete Wavelet Transform (DWT) methods. The extracted features are then fed into the discriminator which is an Artificial Neural Network (ANN) discriminator or a Support Vector Machine (SVM) discriminator. The obtained results prove that the proposed algorithms can be used efficiently for the neutron and gamma ray discrimination purpose and that the DWT based method achieves the highest discrimination rates. For discriminators, the SVM discriminator achieves better performance with a slightly shorter processing time compared to the ANN discriminator.

Comparison of SiPM and PMT Performance Using a ${\rm Cs}_{2}{\rm LiYCl}_{6}:{\rm Ce}^{3+}$ (CLYC) Scintillator With Two Optical Windows

Measurements of thermal neutrons and gamma rays using multiple ${\mathrm{ Cs}}_{2}{\mathrm{ LiYCl}}_{6}:{\mathrm{ Ce}}^{3+}$ (CLYC) crystals with photomultiplier tube (PMT) and silicon photomultiplier (SiPM) are compared. The first set of measurements used three single-sided crystals (two made from 95% enriched 6Li and one made with 99% enriched 7Li) mated with the PMT and SiPM to compare the energy resolutions and figures of merit (FOM) for the pulse shape discrimination of gamma rays and neutrons. All crystals and photomultipliers were able to resolve full-energy photopeaks for 137Cs and 60Co and distinguish gamma-ray interactions from neutron interactions ( $\text {FOM} > 1$ in all cases) while operating in a thermal neutron environment. Measurements made with the PMT had better energy resolution, and switching to the SiPM degraded the energy resolution by an average of 34.0± 0.7% (at 662 keV). The second set of measurements used a CLYC crystal with two optical windows to enable simultaneous measurements with the PMT and SiPM. Once again, both photomultipliers were able to distinguish gamma rays from neutrons, and the PMT had the best energy resolution. However, in this case, the SiPM was not able to resolve the 137Cs full-energy photopeak, and neither photomultiplier could resolve any photopeaks if 60Co was used simultaneously. The degradation in energy resolution was due to the relative splitting of scintillation light intensity between each photomultiplier depending on the position of the interaction site within the crystal. Each pair of waveforms recorded from the PMT and SiPM, corresponding to a single interaction within the double-sided crystal, were combined to improve the energy resolution at 662 keV from 15.9 ± 0.9% to 12.7 ± 0.3% and the FOM from 1.850 ± 0.004 to 2.117 ± 0.003 when compared to the data just from the PMT.

A technique for the reduction of pulse pile-up effect in pulse-shape discrimination of organic scintillation detectors

Abstract A technique for the reduction of pulse pile-up effect in digital pulse-shape discrimination (PSD) of neutrons and gamma-rays with organic scintillation detectors is presented. The technique is based on an electronic reduction of the effective decay-time constant of scintillation pulses while retaining the PSD information of the pulses. The experimental results obtained with a NE213 liquid scintillation detector in a mixed radiation field of neutrons and gamma-rays are presented, demonstrating a figure of merit (FOM) of 1.20 ± 0.05 with an energy threshold of 350 keVee (electron equivalent energy) when the effective length of the pulses is reduced to 50 ns.

Distance metrics for digital pulse-shape discrimination of scintillator detectors

Digital pulse-shape discrimination (PSD) of scintillator detectors has gained popularity as an efficient technique for the discrimination between different types of particles. In this paper, we have investigated the use of simple distance metrics for digital PSD of neutron and gamma-rays in liquid scintillator detectors. The distance metrics are commonly used in the field of pattern recognition and offer the advantage of a simple and effective performance. Our method is based on quantifying the difference between a sampled detector pulse and an ideal step pulse. For this purpose, some of the common distance metrics including Euclidean, City-block, Canberra, root mean square (RMS) and Hellinger were experimentally examined through the discrimination of neutrons and gamma-rays in a liquid scintillator detector and their performances were compared to that of the conventional charge-comparison method. It was found that the City-Block distance metric exhibits a very simple and effective PSD approach by producing a figure-of-merit (FOM) of 0.72 against a FOM = 0.54 for the charge-comparison method in the very low light output range of below 160 keVee (electron equivalent energy) and a mean FOM value of 1.23 over the whole examined light output range of 60–1000 keVee.

Assessment of Performance of New-Generation Silicon Photomultipliers for Simultaneous Neutron and Gamma Ray Detection

Significant interest in silicon photomultipliers (SiPMs) over the last decade has spurred impressive growth in their technology, both in terms of performance and selection of SiPMs with differing characteristics. Nuclear nonproliferation and safeguards is a field of particular relevance for the development of SiPMs as they have been shown to be capable of simultaneously detecting gamma rays and neutrons when coupled with organic scintillators and utilizing pulse-shape discrimination (PSD). As such, an assessment of the state of the art in SiPM technology and study of the impact certain SiPM characteristics have on performance in different applications is required. This paper characterizes the performance of 20 different SiPMs from five manufacturers with pixel sizes ranging from 3 to 6 mm and microcell size ranging from 15 to $75~\mu \text{m}$ . Emphasis is placed on the ability to discriminate between neutrons and gamma rays when coupled to organic scintillator stilbene as a function of overvoltage, as well as the noise. Comparison with a fast photomultiplier tube (PMT) shows that current generation SiPMs perform competitively with PMTs in PSD, and it is found that SiPMs with larger microcells tend to have more effective neutron–gamma ray discrimination capability.

Improved Lithium Iodide neutron scintillator with Eu[formula omitted] activation II: Activator zoning and concentration effects in Bridgman-grown crystals

We have previously reported on the formation of Suzuki Phase precipitate particles as a result of the addition of the divalent activator ion Eu 2+ to the monovalent alkali halide host LiI. [Boatner et al. (2017)]. These precipitates form during Bridgman or other melt-growth processes, even at low Eu2+ concentrations (e.g., 0.1% EuI2 doping), and scatter the scintillation light reducing the optical transparency of the scintillator and adversely affecting its radiation-detection performance. In our prior work, we developed a two-stage thermal-treatment method for the post-growth removal of the Suzuki Phase particles and the realization of a significant improvement in the optical transparency and associated neutron-detection of LiI:Eu2+ scintillators. These improvements resulted in neutron-detection performance that is superior to GS-20 glass and that allows for the application of pulse height gamma-ray discrimination over a wide range of gamma ray energies as opposed to pulse shape discrimination. Here, we apply the two-stage thermal-processing method for the removal of Suzuki phase precipitates and carry out an in-depth study, first, of the neutron scintillator performance versus the Eu2+ activator-ion-concentration spatial variation as a result of zoning effects during the Bridgman growth of LiI:Eu2+ and, second, of the effects of varying the initial Eu2+ activator ion concentration prior to crystal growth. The Eu2+ zoning variation results allow one to identify and select the most efficient location of the scintillation performance in a directionally solidified single-crystal boule. The present study of the initial activator concentration levels shows that there are, in fact, two distinct types of luminescence centers with varying performance properties — one that occurs only at low EuI2 addition levels (e.g., 0.01 to 0.06 %EuI2) and that is quickly replaced by a second luminescing center with increasing Eu2+ content (e.g., at ∼0.1% EuI2). The light yield for the luminescing center formed using a Eu activator in LiI is a critical function of the Eu concentration in the range of 0.01 to 0.1 % EuI2, and a high light yield of 100,000 photons/neutron is observed at the 0.06 %EuI2additive level prior to thermal processing.

Selection of silicon photomultipliers for a 6LiF:ZnS(Ag) scintillator based cold neutron detector

We describe the process of selecting a silicon photomultiplier (SiPM) as the light sensor for an ultrathin (≈2 mm) highly efficient cold neutron detector. The neutron detector consists of 6LiF:ZnS(Ag) scintillator in which wavelength shifting (WLS) fibers have been embedded. The WLS fibers conduct the scintillation light out from the scintillator to the SiPM photosensor. In addition to the many benefits of using silicon photomultipliers as photosensors (low cost, compact size, insensitivity to magnetic fields), their selection also presents many challenges (thermally induced dark noise, delayed cross talk, afterpulsing, etc) which are not shared by traditional photomultiplier tubes. In this work, we discuss the considerations for the selection of the appropriate silicon photomultiplier to achieve the best net neutron sensitivity and gamma ray discrimination. Important characteristics for these devices include short recovery time (≈35 ns), high photodetection efficiency (>30% at the target wavelength), low thermal noise (<35 kHz mm−2 at ambient temperatures), and low crosstalk.

Development of real-time thermal neutron monitor array for boron neutron capture therapy

Background: We have performed over 500 boron neutron capture therapy (BNCT) clinical studies using a research reactor. Irradiation time is evaluated by the measured neutron flux using gold activation methods at the surface of the affected area. To perform highly accurate BNCT treatment, it is desired to measure thermal neutrons in real time. Methods: We have developed a real-time thermal neutron detector array using a small scintillator combined with a quartz fiber to fulfill the required characteristics, including count rate, neutron field disturbance, radiation resistance, and gamma ray discrimination. A characteristic test was performed using reactor- and accelerator-based neutron sources. Results: We present the result of the performance test. One scintillator combined with a quartz fiber can measure the trends of thermal neutron flux up to 10 9 (n/cm 2 /s) using an accelerator-based neutron source. The newly developed detector array can also measure the one-dimensional thermal neutron flux up to 10 9 n/cm 2 /s. Furthermore, it is confirmed that a two-dimensional thermal neutron distribution can be measured by scanning with our developed detector array. Conclusions: A real-time neutron detector array was developed. According to the irradiation test using accelerator- and reactor-based neutron sources, it was confirmed that the developed system fulfilled the required characteristics.

Novel concept for neutron detection: proportional counter filled with 10B nanoparticle aerosol

The high neutron detection efficiency, good gamma-ray discrimination and non-toxicity of 3He made of proportional counters filled with this gas the obvious choice for neutron detection, particularly in radiation portal monitors (RPM), used to control the illicit transport of nuclear material, of which neutron detectors are key components. 3He is very rare and during the last decade this gas has become increasingly difficult to acquire. With the exception of BF3, which is toxic, no other gas can be used for neutron detection in proportional counters. We present an alternative where the 3He atoms are replaced by nanoparticles made of another neutron sensitive material, 10B. The particles are dispersed in a gaseous volume, forming an aerosol with neutron sensitive properties. A proportional counter filled with such aerosol was exposed to a thermal neutron beam and the recorded response indicates that the neutrons have interacted with the particles in the aerosol. This original technique, which transforms a standard proportional gas mixture into a neutron sensitive aerosol, is a breakthrough in the field of radiation detection and has the potential to become an alternative to the use of 3He in proportional counters.