This PDF file contains the front matter associated with SPIE Proceedings Volume 13151, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Many scintillator materials have been used as a single crystal with high transparency and the quality affects the luminescent and scintillation properties. We have developed advanced crystal growth techniques that lead to the material research of novel scintillator single crystals and device implementation of scintillators. Shape-controlled scintillator single crystals were grown from the melt directly by the micro-pulling-down (μ-PD) method using specially designed crucibles. In addition, fiber and bulk single crystals of halide scintillator with high hygroscopicity could be grown by the halide-μ-PD (H-μ-PD) and halide-Vertical Bridgman (H-VB) methods. Recently, we developed the growth method using a tungsten crucible for oxide scintillator single crystals with high melting point over 2200°C.

Currently, there are 4 existing methods that are used for alpha particle detection in water: Gas flow proportional counter, PMT-based scintillation counter, liquid scintillation counting and alpha-particle spectrometry. However, NONE of these existing methods can be tested directly in water or in real-time due mainly to the limitation of the detector material itself as well as associated device design. These existing detector technologies all require some form of evaporation, sample preparation as well as laboratories test procedures in the lab, which is clearly not practical for time-critical situations as in war-fare environment or future threads. In this work, we report the development of a novel scintillation detector material and its associated device design, the ultra-compact, lightweight SiPM-based Hg2Br2 scintillation detector that can directly detect gross alpha in drinking water in the field, and in real-time while being wearable as needed, especially for soldiers and military personnel in general. This novel detector does not require test sample preparation. Besides environmental and health safety, the detector also has additional capabilities such as energy discrimination and good counting efficiency so that it can be practically used in low radioactivity scenarios. Moreover, the novel Hg2Br2 scintillation detector material is also simultaneously capable of detecting other forms of radiation emanating from radioactive materials, including dual gamma-neutron detection capability, and having excellent radiation hardness.

Elpasolite scintillators show great promise for dual mode neutron-gamma radiation detection and imaging but the impact of high dose radiation on performance characteristics has not been evaluated. Crystalline (Cs,Tl)₂LiLaBr₆:Ce (CTLLB) materials are grown. After growth the 1-inch diameter crystals are processed and packaged. Prior to the irradiation sequence at SRNL, the detector performance of the encapsulated crystal is measured with gamma-ray check sources including ¹³⁷Cs and ¹⁵²Eu. Properties such as energy resolution, light yield, proportionality behavior, and decay times are measured. The packaged crystal is irradiated four times at dose rates of 1, 10, 100 and 1,000 Gy of absorbed dose in a ⁶⁰Co irradiation and the performance of the crystal is evaluated before and after each radiation treatment. Cumulative dose rates between irradiation were 1, 11, 111 and 1,111 Gy. Initial results show a decreased measured light yield after each radiation exposure, however further analysis on the packaging materials will be pursued.

The inorganic scintillation crystal, Cs₃Cu₂I₅, has garnered considerable interest from the nanocrystal, thin film, and bulk crystal communities. Its non-toxic composition, cost-effectiveness, air stability, good light yield, high density, reasonable decay time, and visible wavelength compatibility with several photodetectors make the bulk Cs₃Cu₂I₅ crystal a promising candidate for a wide range of applications, including optoelectronics, x-ray and γ-ray radiation detection. Further studies reveal a low-dimensional metal halide structure with a suggested self-trapped exciton and complex trap processes. This implies that there is potential for further research into the luminescence and scintillation of this crystal to optimize its performance. Based on the self-trapped exciton mechanism with the goal of room-temperature application, activated scintillation has been considered. The monovalent activation center could be a good candidate for study. Following the same concept in well-known CsI crystals, the Cs₃Cu₂I₅:Tl and Cs₃Cu₂I₅:Ag crystals were studied in this work. These crystals were synthesized and grown using the Bridgman technique. The good parts of the crystal were cut and polished. The scintillation characteristics were measured using the Hamamatsu R6233-100 photomultiplier tube (PMT) with emission wavelengths well-matched to these crystals. Data acquisition and analysis were performed using a 500-MHz flash analog-to-digital converter (Notice, Korea) with a CERN ROOT-based program. The absolute light yield was measured using the PMT single photoelectron technique. The pulse shape study, including decay time and particle discrimination, was investigated for γ rays and α particles. The charge comparison method with optimization was used for pulse shape discrimination. Our results showed the potential application not only for x-ray and γ-ray measurements but also for α measurements. However, the unexpected inverse performance of these activation centers was observed, leading to the motivation for luminescence investigation. This work compared the x-ray luminescence of these doped crystals to other related crystals. For this purpose, CsI, CsI:Cu, CsI:Ag, and intrinsic Cs₃Cu₂I₅ crystals were grown. It suggests a complex energy transfer to the Tl⁺ and Ag⁺ activation centers regarding the Cu⁺ ion in the electronic structure. Our study indicates that these crystals have the potential to be effective scintillators for room-temperature applications. These applications include radiation detection and measurement (x-rays, γ rays, and α particles), radiography (such as medical imaging and defect inspection), and rare event searches as promising candidates for dark matter search.

Metal halide perovskite (HP) scintillation crystals have garnered significant interest due to their potential to enhance radiation detection efficiency across various applications. Their notable scintillation properties and competitive optical performances make them strong candidates for advanced radiation detectors. This study investigates gamma-ray detection using a perovskite Cs₃Cu₂I₅ scintillator grown via the inverse temperature crystallization method. Formic acid was used to prevent oxidation of the iodine and copper ions, enabling the production of samples of appropriate size for effective gamma-ray detection. The grown Cs₃Cu₂I₅ samples were subsequently cleaned with dimethyl sulfoxide and dimethylformamide to optimize their condition. A 10×10×6mm³ Cs₃Cu₂I₅ scintillator was covered with a Teflon tape and coupled to a photomultiplier tube (PMT) using an optical grease to measure the energy spectrum. The collected scintillation light on a digitizer was converted as an electrical signal, and analyzed on a PC. The energy resolution with an irradiation of ¹³⁷Cs source was 12.5% at 662keV. The maximum transmittance was recorded at 82.1%, as measured using a UV-Vis-NIR spectrometer. The findings of this study offer promising insights for future research and technological development in various fields.

The Lunar Vulkan Imaging and Spectroscopy Explorer (Lunar-VISE) mission consists of a suite of instruments to explore the Gruithuisen Domes located in the northern lunar hemisphere. One of instruments to be mounted on a rover is a gamma ray and neutron spectrometer. The spectrometer uses a Li-6 enriched Cs₂⁶LiYCl₆ (CLYC) scintillator to detect both gamma rays and neutrons. The design of the instrument balances mass, power and performance to obtain high-quality gamma ray spectroscopy with a 6.4-cm diameter, CLYC crystal encased in a gadolinium shell to veto thermal neutrons. To obtain a measure of the thermal neutron albedo to assess the concentration of local neutron moderating materials, a 5.0-cm diameter CLYC without a gadolinium shell is used to measure the full spectral, neutron flux. To minimize power, the system design utilizes a multi-channel configuration to provide pulse shape analysis and spectroscopy using a single, readout channel.

We report on the on-orbit performance of the Glowbug instrument, which operated on the International Space Station (ISS) from March 2023 to April 2024. Glowbug is a NASA Astrophysics Research and Analysis (APRA) funded instrument built by the U.S. Naval Research Laboratory (NRL) in Washington, DC, and is the pathfinder instrument for the upcoming NASA StarBurst Multimessenger Pioneers mission. Glowbug was launched to the ISS on the 27th Commercial Resupply Services mission operated by SpaceX (SpX-27) as part of the Department of Defense Space Test Program (STP) H9 pallet. Glowbug’s primary science objective is the detection and localization of short Gamma-Ray Bursts (GRBs), which are the result of mergers of stellar binaries involving a neutron star with either another neutron star or a black hole. Detection is enabled by 12 large area (150mm x 150mm), inorganic scintillator panels (thallium-doped cesium iodide, CsI:Tl), arrayed on the surface of a half cube. Each panel is read out on one edge by a 1x21 array of onsemi J-series 6mm x 6mm silicon photomultipliers (SiPMs). Additionally, within the half cube, resides two inorganic scintillators, Cs₂LiLaBr₆:Ce (CLLB), and a small plastic (EJ-200) scintillator on the exterior used as an South Atlantic Anomaly (SAA) entry and exit detector, both of which are read out by an array of SiPMs on one face of each detector unit. We discuss the Glowbug on-orbit results for one year’s worth of data, in terms of on-orbit operations, SiPM performance in low-earth orbit (LEO), and GRB detections.

The operation of nuclear instruments in high-radiation environments is critical for a myriad of applications, which include intense particle beams for future science experiments, in-situ measurements for emerging and advanced nuclear fuel cycles, or operation in a diverse range of environmental and harsh radiation conditions for military applications. A common tool used to measure ionizing radiation is scintillation materials, which produce a light pulse with an intensity proportional to the energy deposited, where a photodetector is used to measure the light pulse. A photodetector sensitive enough for scintillator readout is the photomultiplier tube, yet these devices are typically bulky. Though SiPMs, formed from an array of single photon avalanche photodiodes, or Geiger photodiodes (GPD), are replacing photomultiplier tubes, they are susceptible to radiation damage. This work discusses new technologies of GPDs consisting of GaAs and AlGaAsSb for operation in intense radiation and environmental conditions.

The Remote Sensing Laboratory–Andrews (RSLA) initiated an advanced robotic systems feasibility study project under the Site Directed Research and Development (SDRD) in 2023. Two prototype systems with radiation detection sensors were developed and tested for use in the forensics investigation of debris produced from explosively dispersed radioactive materials. To automate the robots, an Arduino microcontroller was added, and instead of reading signals directly from the radio control receiver, the system takes signals from the motor controller. The robots can be programmed to drive various search and survey patterns. Mapping results obtained by deploying this robotic system will be presented. The Arduino microcontroller system was chosen for this project for its value as a prototyping tool. Specifically, the Mega 2560 R3 model was chosen for its multiple data inputs and low power draw, allowing it to be integrated into the originally designed robotic system without requiring additional power capacity. The Arduino system is designed to be easily modified and can serve as a proof of concept for further development with proprietary systems in the future. The system was programmed in C++ using the Arduino IDE (Integrated Development Environment). Issues arose during development when attempting to use the software library developed by the manufacturer of the Sabertooth controller, but when that was replaced in favor of a standard motor control library, the robot functioned as intended. The prototypes used to measure a baseline ground truth of a radiation field; these will be compared to low flying Unmanned Aerial Systems (UAS) for optimizing flight profiles.

Explosive devices typically consist of several common materials, most of which have differing densities. When these materials are imaged through x-ray imaging, the resultant image displays differing contrast intensities within due to the scattering effects of these materials. These intensities provide shape and definition to the operator conducting the imaging, informing their decision making as to parts and components within the suspected device. A power source the size of a battery, or a piece of shrapnel, such a ball bearing, would have a noticeably different appearance than that of plastic explosives. The purpose of this research is to enhance single sided Compton Backscatter Imaging (CBI) of suspected explosive devices to support operators investigating a suspected device. Previous research by the team at UF in material discrepancy utilized Modulation Transfer Functions (MTF) derived from bar patterns of decreasing size to characterize a linear detector array and determine the maximum resolution in a CBI configuration. The previous research expanded into Edge Spread Functions (ESF) of these materials as a secondary method of characterizing material differences. This research explores the Slant Function, a derivative of the ESF, of differing materials to improve the ESF characterization. This occurs through a single edge analysis along every pixel of a linear detector array, comparing local intensities of the imaged edge to determine the cumulative effect on the overall ESF. This will allow for better MTF development, thereby enhancing filters developed for image post processing.

The Nuclear Imaging System at the National Ignition Facility (NIF) collects primary and downscattered neutron, x-ray, and gamma-ray images of inertial confinement fusion implosions. Penumbral and pinholeprojection images are recorded using scintillators coupled to fast-gated intensified cameras. Successful reconstruction relies on accurate characterization of the imaging system sensitivity, which can vary by up to a factor of 2 across the field of view. Historically, this has been accomplished by using NIF shots without the aperture to uniformly illuminate the detector, or to project onto it a grid pattern from a fiducial plate to correct for detector sensitivity and optical system aberrations, respectively. However, frequent changes to the imaging system due to equipment failures or vibrations within the building have increased the need for calibrations, which are limited in availability to approximately once per year because they require sacrificing imaging data on a neutron-producing shot. We present development work on an optical calibration system that will enable the collection of this data without that requirement promptly, easily, and at regular intervals.

Micro-channel plate (MCP) detectors have long been a workhorse for space-based x-ray research and are advantageous over other imaging detectors because of their low size, weight and power. The Lunar Environment heliospheric x-ray Imager (LEXI), will utilize a MCP to image Earth’s magnetosphere in soft x-rays from the lunar surface. A critical element for interpreting on-orbit data is to understand the quantum detection efficiency (QDE) of the MCP. LEXI’s MCP is coated with potassium bromide (KBr) to increase the soft x-ray QDE. Historically, few measurements of QDE exist in the soft x-ray band for KBr detectors. This paper reviews the performance of LEXI’s detector, and the QDE experiment procedure conducted at and results from the Advanced Light Source synchrotron soft x-ray beam line (6.3.2) over the energy range 70eV-1300eV. A unique beam line setup was required to limit the photon flux as to not saturate the pores of the MCP or detector signal chain. The experimental results are similar to previous literature, with some caveats unique to this MCP and experimental setup.

As semiconductor radiation detectors, detectors with high sensitivity at high energy, such as cadmium telluride (CdTe), which we have reported for many years, have been mainly developed, but CdTe has a K-edge and its attenuation coefficient at low energy, around 30 keV or lower, becomes small. there is a need for semiconductor detectors made of other materials that can be used for low-energy applications such as mammography. We propose gallium nitride (GaN) as a new semiconductor detector material, aiming at a useful detector in the low-energy region targeting 17.5 keV, where characteristic x-rays are generated. GaN has also been studied for LED and power devices, and its excellent charge transfer characteristics have been demonstrated in practical applications. In order to investigate the feasibility of GaN as a semiconductor material for radiation detectors, we fabricated pn-type and pin-type GaN detectors and evaluated their current-voltage characteristics, capacitance-voltage characteristics, and x-ray response characteristics. From the results, diode characteristics were confirmed for both structures. However, the frequency dependence of the capacitance-voltage characteristics of the pn-type detector suggested that the pn-type detector had many internal defects in the crystal. In both structures, the detected current increased with x-ray irradiation, and the current increased linearly in the range of the measured dose rate. In the alpha-ray detection measurement at an incident energy of 3.6 MeV, the pin-type detector was found to be sensitive to alpha rays. However, the pn-type detector did not detect the pulse because the pulse was buried by fluctuations due to leakage current and thermal noise. It was also shown that the pin-type detector must have a small dark current to make gamma-ray detection measurements with low energy. The results show the feasibility of GaN as a semiconductor material for radiation detectors, and both the pn-type and pin-type detectors exhibit linear current increase in the x-ray response characteristics measurements, suggesting the feasibility of GaN as a storage-type x-ray detector. In addition, the pin-type detector showed pulses of alpha-rays, suggesting the feasibility of a photon-counting type detector for gamma-rays in the future.

Silicon carbide (SiC), particularly the 4H-SiC polytype, is a maturing wide bandgap semiconductor that has been shown to be an optimal material for high performance electronics in extreme environments. Conventional semiconductor radiation detectors have been shown to have limited performance above room temperature, with loss of sensitivity and degradation of detector resolution due to increase in electronic noise. The wide bandgap (3.27eV) of 4H-SiC and the variable active region of Schottky barrier diodes produce a device capable of maintaining a lower-level of electronic noise, even at elevated temperature. We fabricated 4H-SiC Schottky barrier diodes and evaluated their electrical parameters using current-voltage (I-V) and capacitance-voltage (C-V) measurements. The I-V and C-V measurements were performed at elevated temperatures up to 500 °C at 100 °C increments. Electrical performance was also measured at room temperature following each thermal cycle. Energy spectroscopy performance of the devices was also measured following each thermal cycle. Detector characteristics such as resolution and peak channel were compared following thermal cycles. However, at low temperatures, the TFE model does not match well with our experimental results. A model where the TFE current and the reverse saturation current (FE model) at room temperature is proposed, and proved a good fit with experimental data from room temperature to 500 C when high bais is applied.

While defects are known to inhibit device level performance, research shows specific spin defects resulting from silicon vacancy, carbon vacancy, or divacancy in SiC are alternative platforms to NV center in diamond for quantum sensing. Multiple 4H-SiC Schottky barrier diodes (SBD) were in-house fabricated and irradiated with ²⁴¹Am alpha particles to a total accumulated fluence between 1×10¹³-1×10¹⁴ cm^-2 over about 2-years low dose irradiation at room temperature. These irradiated devices, after annealing, were electrically characterized using I/V and C-V measurements and electron paramagnetic resonance (EPR) spectroscopy for the concentration of electronic active traps, atomic and electronic structure. The EPR spectroscopy shows that alpha irradiation induces changes in the properties of paramagnetic sites in 4H-SiC. Differences include increased line width and distorted line shape in irradiated samples, suggesting changes in relaxation behavior. Slight differences in g-values suggest possible changes in the paramagnetic sites due to irradiation. The temperature dependence studies conducted on vacancy sites, however, is inconclusive in identifying carbon and silicon vacancies or nitrogen donors in 4H-SiC, due to signal saturation at temperatures below 100 K.

Quantum sensing utilizes the inherent sensitivity of a quantum system to external stimuli. Our goal is to leverage this sensitivity to develop a quantum sensor designed for the detection of ionizing radiation. Here we report on the design, fabrication, and measurement of a new quantum device for hard x-ray and gamma-ray detection. Our quantum device is based on a superconducting quantum bit (qubit) with superconducting tunnel junctions as the core device elements. We describe our experimental investigation directed toward the detection metrics of energy resolution, dynamic range, and active area. In contrast to existing superconducting detectors, the active area per qubit may be much larger than the physical area of the tunnel junctions or the physical area of the qubit device, due to the sensitivity of quantum coherence to ionizing radiation deposition within a radius on the millimeter or centimeter scale. Our experimental design enables an ionizing radiation source at room temperature to be detected by our quantum sensor at low temperature.

In recent years, research using Mixed Reality (MR) has attracted attention in the medical field, especially in radiology, where data captured by X-ray CT and MRI can be represented in 3D and combined with real space to aid diagnosis and simulate surgery. On the other hand, surface and volume rendering are mainly used for 3D rendering. It is difficult to grasp the internal structure only from the rendered data due to differences in rendering thresholds, and the information displayed is different from that of Multi-Planar Reconstruction (MPR) images as shown in 2D, so it is difficult to grasp the internal structure only from the rendered data. Also, general three-plane MPR images of sagittal, axial, and coronal sections differ from the practitioner's viewpoint when looking at the patient. This study aims to represent the 2D MPR image according to the viewpoint direction from which the practitioner views the patient and represents them in MR real-time. In the experiment, the system being proposed uses a head-mounted display (HMD) equipped with a camera see-through function that calculates the angle at which the practitioner views the patient utilizing the bed position as the central coordinate, generates MPR images from DICOM according to that angle, and displays them superimposed on the real space. As a result, the practitioner could check the internal structures of the patient's body according to their viewpoint direction with MPR images in MR.

X-ray fluorescence imaging (XFI) is a non-invasive technique enabling key applications such as pharmacokinetic studies and immune cell tracking. Labeling with medium to heavy elements enables detection by excitation with hard x-rays and subsequent measurement of emitted characteristic radiation. XFI provides high spatial resolution, high sensitivity and provides quantitative data. Special requirements need to be fulfilled by the x-ray detectors to reach a high sensitivity. These include high energy resolution, detection efficiency, large active area, and throughput, while minimizing noise from internal detectors effects. Here we discuss recent XFI applications in preclinical imaging and experiences with various detector types.

A comparative analysis of the ¹³⁷Cs isotope spectra measured both by single and series-connected Cr/CdTe/Au diodetype X/γ-ray detectors has been conducted. Rectifying (Cr) and ohmic (Au) contacts were respectively formed on the Band A-faces of detector-grade CdTe(111) crystals after Ar plasma surface processing. The diode sandwiches (stacks) were created by staking and connecting in series two Cr/CdTe/Au Schottky diodes with similar parameters. A key feature of the ¹³⁷Cs isotope spectra obtained from these sandwiches was the presence of two peaks with maxima and energy positions (channel numbers) depending on the CdTe crystal thickness and relative positions of the diodes in the sandwich. The sum of channel numbers corresponding to these peaks equaled the channel number of the peak in the spectrum obtained by a single diode. Even when Cr/CdTe/Au diodes of different thicknesses were used in the sandwich, the sum of the channel numbers corresponding to two peaks in the ¹³⁷Cs spectra remained constant. The heights (maxima) of the two peaks were much higher than the peak height the spectrum measured by a single diode. The series-connected Cr/CdTe/Au Schottky diodes detected X/γ-rays much more effectively than a single detector at a bias voltage equal to half that applied to the sandwich. Another advantage of the diode sandwiches was the time stability of their characteristics. The ¹³⁷Cs isotope spectrum degraded during 8 hours of measurement by a single detector, while no noticeable changes were found in detection efficiency and energy resolution when the sandwich detectors were used.

Room temperature semiconductor detectors provide high energy resolution in gamma-ray spectroscopic applications, such as radioisotope identification. Materials such as TlBr and CsPbBr3, which provide ~2% FWHM, or better, energy resolution for 662-keV photopeak from Cs-137 irradiation at room temperature and high stopping power, nevertheless exhibit mixed electronic and ionic conduction that can lead to undesirable performance degradation. While the charge pulses generated by the gamma-ray interaction and a component of the leakage current are composed of a dominant electronic signal, the ionic component contributes to the current. It affects device stability via the migration of ionic species under applied bias and polarization at the semiconductor-electrode interface, interfering with charge collection. In this work, we characterize electronic and ionic conduction in single-crystal devices of TlBr and CsPbBr3 (CLB) using ionically blocking electrodes. The ionic contribution to the leakage current is evaluated from the devices' impedance spectra. In contrast, the electronic contribution is extracted from the asymptotic limit of the devices' current-voltage-time (iVt) plots for different bias values. The response to illumination with a 375-nm LED is also measured in the iVt plots. This work presents expressions for the temperature dependence of the conductivity, referencing previous work for TlBr. It also presents the gamma-ray spectra's bias dependence and evaluates ionic conduction's role in device burn-in, conditioning, and aging processes. Comparing the impedance spectra with and without LED illumination confirms that ions represent the majority charge carrier at room temperature for TlBr and CLB, which is consistent with previous work.

The electro-physical properties of Cd_0.96Mn_0.04Te_0.96Se_0.04 n-type conductivity single crystals with relatively low resistivity were studied. The determined resistivity of semiconductor single crystals Cd_0.96Mn_0.04Te_0.96Se_0.04 n-type conductivity is equal to ρ≈2 Ω-cm at 293K. The activation energy of dark conductivity, measured from the temperature dependence of the resistivity of the In/Cd_0.96Mn_0.04Te_0.96Se_0.04/In structure, is equal to ΔE≈0.11eV. From optical measurements of the absorption coefficient from the energy of photons in the region of large α, the band-gap width of the single crystal was found, which is equal to E_g=1.53eV. Diode structures of Ni/Cd_0.96Mn_0.04Te_0.96Se_0.04/In obtained by vacuum sputtering of Ni on the surface of a single crystal n-Cd_0.96Mn_0.04Te_0.96Se_0.04 were manufactured and studied. The rectification coefficient at a voltage of U=1V is equal to 10⁸. Within the framework of the Sah-Noys-Shockley carrier generation-recombination model, a quantitative match of the experimental measurements of the volt-ampere characteristics with the calculation was achieved.

The melting behavior of CsPbBr₃ perovskite was studied by differential thermal analysis (DTA). It was found that melting of CsPbBr₃ occurs non-isothermally in the temperature range of 561 to 570 °C. From the temperature dependence of the solid-phase melting rate, it was established that at 567±1 °C the change in the mechanism of the solid-phase melting goes from fragmentation to dissolution at the surface. The obtained values of the activation energy of the melting of the solid phase in CsPbBr₃ show that the activation energy of the dissolution of the solid-phase fragments is 4 times greater than the energy of the fragmentation of the solid phase.