Recent works have implemented machine learning based solutions for many complex classification tasks including pulse shape discrimination in radiation detection. The present work aims to advance the application of machine learning to pulse shape discrimination in neutron detection. A machine learning based neutron-gamma discrimination technique is investigated for various neutron energy distributions produced from DD, DT, (α,n), and spontaneous fission neutron sources. Comprehensive investigations on the training data generation techniques, the impact of the PMT bias, and the discrimination performance are conducted. With the increase of the PMT bias voltage, the neutron classification performance peaked at 1500 V with 81 % of validation neutrons being identified at a false positive rate of 1E-6 while the further bias increase led to a notable degradation in performance. The unsatisfactory classification performance encountered when training off of one neutron source type and classifying neutrons from the other source types was greatly improved with the application of the transfer learning techniques. The remaining variation in the performance was accounted for by the energy dependence of the neutron classification. It was demonstrated that at the 1E-6 FPR specificity level, the events within the region of overlap for neutron and photon populations could be separated, down to a detected energy of 30 keVee. An overall intrinsic neutron detection efficiency of 12.5 % was achieved for the 252Cf neutron source at a false positive rate of 1E-6.

Position sensitivity enables the correction of response non-uniformities in room-temperature semiconductor detectors caused by crystal defects and other factors. It can also be used to pinpoint the exact location of crystal defects responsible for the response variations. This work describes a technique for revealing and visualizing the detector regions affecting the charge collection efficiency in CdZnTe (CZT), TlBr, and CsPbBr3 detectors configured as position-sensitive virtual Frisch-grid (VFG) devices. The technique correlates the photopeak events in energy spectra with their spatial distributions inside the detectors using the position information. By selecting the events from narrow energy intervals within a photopeak, we can visualize the detector volumes with particular charge collection efficiencies, which, in turn, correlate with the locations of electrode and crystal defects. We demonstrate this technique in several examples. Columnar structures in the volume plots (position distribution maps) are consistent with signal losses near or at the anode in selected samples of CZT and TlBr. Structures exhibiting a distinct depth dependence are consistent with grain boundaries or other crystal defects.

This work evaluates data from position-sensitive capacitive Frisch-grid (PS-CFG) TlBr detectors for correcting the gamma-ray energy spectrum based on the location of the interaction in the crystal. This enables the correction of non-uniformity in the signal response. Signals from 5×5×12 mm 3 TlBr PS-CFG detectors generate anode amplitude versus cathode-to- anode-ratio histograms, which map the interaction depth for a 32×32 grid of XY pixels. The width of the 662-keV photopeak from 137 Cs irradiation contains contributions from statistics and non-uniformity. The dependence of the signal on the interaction depth produces an asymmetric "tail" in the photopeak in the anode spectra. This work also evaluates the dependence of the non-uniformity corrections on long-term stability, while under constant 1500 V bias at room temperature after 3 and 5 months of operation. The 3D corrections compensate for some non-uniformity; however, the interaction location determined by the approach represents the centroid of the charge distribution. Variations in the sampling of non-uniformities produced by the shape of the charge distribution may not be corrected. We suspect that the current energy resolution may be limited by uncorrected non-uniformities.

Arrays of 3D position-sensitive detectors (3DPSD), operating at room temperature and using cadmium zinc telluride (CZT) and thallium bromide (TIBr) sensors, are suitable for gamma-ray spectrometry in many applications. One detector configuration, the 3D position-sensitive Virtual Frisch-Grid detector (VFG), is particularly advantageous for integrating into large area arrays. The signals generated inside each detector of the array are captured with the anode, cathode and four pads that enable the reconstruction of the position and energy of the ionizing interaction by measurements of amplitude and timing of the signals. For these applications, a low-noise front-end ASIC has been developed, capable of processing bipolar signals (needed because of AC-coupling of certain electrodes). The ASIC can be coupled to an ADC in order to form a compound “waveform digitizer” capable of post-processing the analog signals and determining amplitude and timing information. This paper describes a 32-channel front-end ASIC that is suitable for reading out a 3 × 3 or 4 × 4 element matrix in the VFG configuration. Each channel is composed of a low-noise charge amplifier with an adaptive continuous reset feedback circuit suitable for both positive and negative charge, a first order shaper and a single-to-differential converter output stage. Voltage and current references are all internally generated by 10-bit DACs and the chip is fully controllable with the I 2 C communication protocol. The readout channel response has been verified using the implemented injection circuit. Linear behavior up to ∼75 ke ± with the gain of ∼80 mV/fC, and up to ∼200 ke ± with the gain of ∼30 mV/fC was demonstrated. In conclusion, the first test result waveforms using a 137 Cs radioactive source on a 5 × 5 × 12 mm 3 TIBr crystal are reported.

This work presents results from analyzing position-sensitive capacitive Frisch-grid (PS-CFG) TlBr gamma-ray detectors. As a room-temperature semiconductor detector, TlBr exhibits a high atomic number, high density, and low Fano factor compared to other material. The use of the 3D position sensing technique provides information on the crystal uniformity. This technique presents the spatial variation in the histograms of the anode amplitude versus the cathode-to-anode ratio, necessary for depth correction, for detectors fabricated with 5×5×12 mm 3 TlBr crystals at room temperature operating at continuous bias (1.5 kV) over the course of nine months. This work also presents the temperature dependence of the leakage current for a TlBr PS-CFG detector over the temperature range of -20 to +60 °C, which varies from <0.2 to 40 nA, respectively, along with changes in the spectrum from the anode signal measured with 137 Cs irradiation. This work shows the utility of the 3D technique to evaluate the performance and uniformity of PS-CFG detectors for applications that require high-energy resolution gamma-ray spectroscopy, such as radionuclide identification.

We report precision mass measurements of neutron-deficient gallium isotopes approaching the proton drip line. The measurements of ^60-63Ga performed with the TITAN multiple-reflection time-of-flight mass spectrometer provide a more than threefold improvement over the current literature mass uncertainty of ^61Ga and mark the first direct mass measurement of ^60Ga. The improved precision of the ^61Ga mass has important implications for the astrophysical rp process, as it constrains essential reaction Q-values near the ^60Zn waiting point. Based on calculations with a one-zone model, we demonstrate the impact of the improved mass data on prediction uncertainties of X-ray burst models. The first-time measurement of the ^60Ga ground-state mass establishes the proton-bound nature of this nuclide; thus, constraining the location of the proton drip line along this isotopic chain. Including the measured mass of ^60Ga further enables us to extend the evaluated T=1 isobaric multiplet mass equation up to A=60.

Results from testing of position-sensitive capacitive Frisch-grid (PSCFG) TIBr gamma-ray detectors are presented. Due to its high atomic number, high density, and low Fano factor, TIBr offers excellent energy resolution and high detection efficiency over a wide energy range, thus providing significant advantages over other detector materials commonly used in hand-held instruments. Using high-fidelity 3-D position sensing enables the response non-uniformity caused by defects in the TIBr crystal to be corrected, thereby offering an approach to overcome one of the technical barriers limiting the use of this promising semiconductor material. By utilizing the 3-D position information, temporal and spatial variations of the charge collection efficiency are presented, which provide microscopic characterization of the PSCFG devices. Using the 3-D response correction technique, the best energy resolution measured is <1.6% (FWHM) at 662 keV; it is expected that this resolution will improve further with the introduction of the ASIC-based front-end electronics discussed in this paper. The results presented demonstrate the great potential of PSCFG TIBr detectors and the need for better understanding and control of ionic migration processes in order to achieve good long-term performance.

Room-temperature operable semiconductor gamma-ray detectors offer the potential of superior energy resolution compared to scintillators, which can be valuable in the design of radionuclide identification equipment. To achieve the best energy resolution and simultaneously provide good sensitivity, multiple detection elements must be arrayed to operate in parallel. This paper describes efforts to construct such an array from multiple elements of thallium bromide (TlBr), a material that inherently offers a high interaction probability and photopeak efficiency for gamma rays. The base design of the array comprises capacitive Frisch grid (CFG) elements. A key objective is optimizing the energy resolution of each element, for which the single-carrier characteristics of the CFG design were chosen. Gains are realized through signal processing that accounts for 1-D or 3-D material inhomogeneity and charge collection variations. Fully corrected energy resolution reaches values of 1.6% FWHM at 662 keV.

Background Simultaneous detection of neutrons and gamma rays have become much more practicable, by taking advantage of good gamma-ray discrimination properties using pulse shape discrimination (PSD) technique. Recently, we introduced a commercial CLYC system in Korea, and performed an initial characterization and simulation studies for the CLYC detector system to provide references for the future implementation of the dual-mode scintillator system in various studies and applications. Materials and Methods We evaluated a CLYC detector with 95% 6Li enrichment using various gamma-ray sources and a 252Cf neutron source, with validation of our Monte Carlo simulation results via measurement experiments. Absolute full-energy peak efficiency values were calculated for gamma-ray sources and neutron source using MCNP6 and compared with measurement experiments of the calibration sources. In addition, behavioral characteristics of neutrons were validated by comparing simulations and experiments on neutron moderation with various polyethylene (PE) moderator thicknesses. Results and Discussion Both results showed good agreements in overall characteristics of the gamma and neutron detection efficiencies, with consistent ~20% discrepancy. Furthermore, moderation of neutrons emitted from 252Cf showed similarities between the simulation and the experiment, in terms of their relative ratios depending on the thickness of the PE moderator. Conclusion A CLYC detector system was characterized for its energy resolution and detection efficiency, and Monte Carlo simulations on the detector system was validated experimentally. Validation of the simulation results in overall trend of the CLYC detector behavior will provide the fundamental basis and validity of follow-up Monte Carlo simulation studies for the development of our dual-particle imager using a rotational modulation collimator. Keywords: CLYC, Pulse shape discrimination, Detection efficiency, Monte Carlo simulation, Dual-particle imager

The aim of this work is to develop a gamma-ray/neutron dual-particle imager, based on rotational modulation collimators (RMCs) and pulse shape discrimination (PSD)-capable scintillators, for possible applications for radioactivity monitoring as well as nuclear security and safeguards. A Monte Carlo simulation study was performed to design an RMC system for the dual-particle imaging, and modulation patterns were obtained for gamma-ray and neutron sources in various configurations. We applied an image reconstruction algorithm utilizing the maximum-likelihood expectation-maximization method based on the analytical modeling of source-detector configurations, to the Monte Carlo simulation results. Both gamma-ray and neutron source distributions were reconstructed and evaluated in terms of signal-to-noise ratio, showing the viability of developing an RMC-based gamma-ray/neutron dual-particle imager using PSD-capable scintillators.

Bubble detectors have been used to characterise the neutron dose and energy spectrum in several modules of the International Space Station (ISS) as part of an ongoing radiation survey. A series of experiments was performed during the ISS-34, ISS-35, ISS-36 and ISS-37 missions between December 2012 and October 2013. The Radi-N2 experiment, a repeat of the 2009 Radi-N investigation, included measurements in four modules of the US orbital segment: Columbus, the Japanese experiment module, the US laboratory and Node 2. The Radi-N2 dose and spectral measurements are not significantly different from the Radi-N results collected in the same ISS locations, despite the large difference in solar activity between 2009 and 2013. Parallel experiments using a second set of detectors in the Russian segment of the ISS included the first characterisation of the neutron spectrum inside the tissue-equivalent Matroshka-R phantom. These data suggest that the dose inside the phantom is ∼70 % of the dose at its surface, while the spectrum inside the phantom contains a larger fraction of high-energy neutrons than the spectrum outside the phantom. The phantom results are supported by Monte Carlo simulations that provide good agreement with the empirical data.

Samples of Cs2LiYCl6:Ce (CLYC) scintillator have been characterized using monoenergetic neutron beams in the energy range 4.1–5.5MeV. Four crystals with dimensions (thickness×diameter) of 1″×1″, 1″×2″, and 2″×2″ were evaluated, including one crystal with natural concentrations of Li isotopes and three that were enriched in 6Li. The intrinsic efficiency of CLYC for fast-neutron detection has been determined for the natural-Li crystal. These measurements were translated into reaction cross-sections, and show good agreement with available cross-section data for neutron interactions with the 35Cl component of CLYC. Furthermore, it is shown that the charged-particle energy released in the fast-neutron reactions on 35Cl varies linearly with the energy of the incoming neutron. These results verify the efficacy of CLYC for fast-neutron spectroscopy in a range of applications.

A new scintillator crystal, now known as CLYC (Cs2LiYCl6:Ce), has been under development for over 15 years (1). It was primarily of interest for radiation detection applications because of its good energy resolution for gamma rays (< 4% for 662 keV gamma rays) and its capability for detection of thermal neutrons. The pulse shapes of the signals from the two radiations are different, which allow them to be separated electronically, permitting simultaneous detection of gamma rays and neutrons. The crystal is now commercially available. Early investigations of the neutron response by the current authors (2) revealed that CLYC also responds to fast neutrons. In fact, the good energy resolution of the response under monoenergetic neutron irradiations showed that CLYC was an excellent high-energy neutron spectrometer. This discovery has great impact on the field of neutron spectroscopy, which has numerous, although often specialized, applications. This presentation focuses on applications in counter-terrorism scenarios where neutrons may be involved. The relative importance of the fast neutron response of CLYC, compared to the thermal and gamma-ray response, will be discussed for these scenarios.

Measurements using bubble detectors have been performed in order to characterise the neutron dose and energy spectrum in the Russian segment of the International Space Station (ISS). Experiments using bubble dosemeters and a bubble-detector spectrometer, a set of six detectors with different energy thresholds that is used to determine the neutron spectrum, were performed during the ISS-22 (2009) to ISS-33 (2012) missions. The spectrometric measurements are in good agreement with earlier data, exhibiting expected features of the neutron energy spectrum in space. Experiments using a hydrogenous radiation shield show that the neutron dose can be reduced by shielding, with a reduction similar to that determined in earlier measurements using bubble detectors. The bubble-detector data are compared with measurements performed on the ISS using other instruments and are correlated with potential influencing factors such as the ISS altitude and the solar activity. Surprisingly, these influences do not seem to have a strong effect on the neutron dose or energy spectrum inside the ISS.

The anomalous magnetic moment of the muon is one of the most precisely measured quantities in experimental particle physics. Its latest measurement at Brookhaven National Laboratory deviates from the Standard Model expectation by approximately 3.5 standard deviations. The goal of the new experiment, E989, now under construction at Fermilab, is a fourfold improvement in precision. Here, we discuss the details of the future measurement and its current status.

A series of Monte-Carlo simulations has been performed in order to investigate the response of the bubble detector to monoenergetic neutrons of various energies. The work was driven by the need to better understand the energy dependence of the detector for applications in space, where the neutron spectrum has a significant component with energy of >20 MeV. The response to neutrons in the range of a few keV to 500 MeV has been calculated, and good agreement between the simulations and experimental data is demonstrated over the entire energy range.