We will present an equipment design and technique to produce inorganic halide ceramic scintillators Cs2HfCl6 (CHC) and Tl2HfCl6 (THC). Also presented is initial ceramic processing for compounds with non-congruent melts: elpasolite Tl2LiLaBr6 (TLLB) and Li-based halide Eu-doped LiSr2I5 (LSI). Comparison between the crystal results from the melt growth method and the ceramic fabrication will be presented. Improvements and optimization of CHC and THC ceramic scintillator fabrication are gauged by monitoring the energy resolution and peak position of 137Cs full energy peak at 662 keV. Both ceramic CHC and THC scintillators have similarly good proportionality compared to their single crystal counterparts.

Spectroscopic detection of gamma photons has widespread applications for radiation research, threat detection and medical diagnosis. We report the development of nanocomposite scintillators dissolved in liquid solutions or cured to solid monoliths for gamma photoelectric generation. High-Z nanoparticles are employed to enhance the gamma cross-section, and conjugated organic luminescent compounds are investigated to boost the light yield. Factors affecting the synthesis, optical transparency, light yield and radiation hardness will be discussed.

Plastic scintillators have been widely deployed for γ-ray detection with the promise of fast response, environment stability and ease of scale-up. The light yield of plastic scintillator is moderate compared with their organic single crystal counterpart. To boost the light yield of plastic scintillators, we investigated and synthesized fluorene derivatives as dopants in the polyvinyltoluene matrix to promote the energy transfer and light yield. Various factors affecting the optical transparency, Förster energy transfer efficiency, light yield and scintillation decay were investigated.

Plastic scintillators are widely deployed radiation detectors due to their low cost and environmental ruggedness. Their effectiveness, however, is limited by their low atomic number resulting in low stopping power and poor photopeak efficiency. Here, we compare two different Bi-loaded plastic scintillator formulations to conventional plastic, demonstrating improved spectroscopy and stopping power at the ~18 in3 scale. One approach, Bi-pivalate plastics, uses conventional fluors and may be used as a drop-in replacement for currently deployed plastics such as EJ200. The other approach, Bismuth Loaded Iridium-complex Plastics (BLIP), uses an Iridium-based fluor for higher light yield and higher Bi loading.

The continued advancements of Silicon Photomultipliers (SiPMs) have made them a viable photosensor for low energy pulse shape discrimination (PSD) between fast neutrons and gammas interactions when coupled to an appropriate scintillator. To assess the performance of two such scintillators, Stilbene and EJ-276, we have conducted studies using 6 mm3 scintillator cells coupled to a SiPM. We demonstrate that both scintillators are viable for conducting PSD for interaction energies from 100 keV to several MeV, whilst optimizing the PSD parameter by varying the integration periods used in its metric. Additionally, we have applied machine learning approaches, in particular boosted decision trees, to characterize the importance of each of the pulse features in a PSD assessment. Identifying the potential of PSD in the low energy region through applying a series of cuts on appropriate pulse parameters.

As Silicon Photomultipliers (SiPMs) have become widely accepted photodetection replacements for photomultiplier tubes (PMTs), there is a demonstrable need for compact electronics that operate as front-end systems for high-density SiPM array readout for specialized end-use applications. One such application is fast neutron/gamma pulse shape discrimination (PSD). Currently, various scintillators are being developed and improved for such PSD, and consequently, there is a need for front-end systems capable of providing the required functionality for their readout. We have designed the second version of a prototype application-specific integrated circuit (ASIC), PSD_CHIP. As in the first version, the ASIC integrates a scalable multi-channel readout system with a low noise front-end, real-time PSD, and a highly tunable digital core. Improvements in this version consist of a dual polarity capable front-end, adjustable gain, and two different techniques for the programmable digital delay lines. The ASIC is designed to provide an input dynamic range of order 1MeV energy depositions, depending on the light yield of specific scintillators. The high level of programmability on-chip is maintained in the synthesized digital core. Current targeted end-use applications include neutron cameras and active neutron-tagging systems for nuclear recoil calibration work of dark matter and neutrino experiments.

CdZnTe (CZT) has been the material of choice and a successful commercial material for X-ray and gamma-ray radiation detector applications. However, despite continued research for last three decades, CZT still contains a high density of performance-limiting defects and compositional inhomogeneity in as-grown ingots. Recently, one option has been explored to add a small amount of selenium (Se) in the CZT matrix to improve compositional homogeneity and mitigate many performance-limiting defects. As a result, the quaternary CdxZn1−xTeySe1−y (CZTS) is emerging as a next-generation compound semiconductor for room-temperature gamma-ray detector applications. Nevertheless, it is well known that adding selenium in CdTe/CZT matrix imposes severe alloy/lattice disorder in the ternary and quaternary compounds, and the bowing of the bandgap with an increased Se content is the result of lattice disorder. Hence, the effect of lattice disorder is expected to degrade the crystalline quality of the material. In this presentation, we report our effort on evaluating the crystalline quality of THM-grown CZTS crystals with the optimized composition (Cd0.9Zn0.1Te0.98Se0.02). The as-grown samples were characterized by the low-temperature photoluminescence (PL) experiments and high-resolution X-ray diffraction using a synchrotron light source at Brookhaven National Laboratory (BNL). The full width at half maximum (FWHM) of both the PL and the X-ray rocking curve were observed to be broadened due to the lattice disorder of the quaternary compound, eventually degrading the crystalline quality. This was confirmed through Density Functional Theory (DFT) calculations.

The CdZnTe family finds widespread use as room temperature radiation detectors, with the emerging material Cd_{x}Zn_{1−x}Te_{y}Se_{1−y} showing even more promising properties. Point defects in this material family have traditionally been studied experimentally or with extremely focused theoretical efforts due to shortcomings that prevented fully theoretical treatment of the defect chemistry. Here, we present results of statistical mechanics simulations of point defect concentrations for various THM-grown Cd_{x}Zn_{1−x}Te_{y}Se_{1−y} compositions. Formation energies and trap levels were calculated for these simulations using density functional theory at the screened hybrid exchange-correlation level and supplemented with vibrational data in the harmonic approximation to capture temperature-dependent changes.

Cherenkov light generated in TlBr promptly after the interaction of a gamma photon provides it with a timing resolution <400 ps full width at half maximum (FWHM) for 511 keV energy depositions. Novel Cherenkov-Charge-Induction (CCI) TlBr detectors combine the fast features of the Cherenkov light readout with the conventional readout of semiconductor detectors, which provides good energy and spatial resolutions. CCI TlBr detectors have the potential to offer, simultaneously, excellent energy, timing, and spatial accuracy, and high detection efficiency. CCI TlBr detectors are uniquely positioned to lead the next generation gamma ray detectors for applications that require high timing accuracy.

TlBr is a promising material for room-temperature semiconductor gamma-ray detectors currently under development by several groups around the world. TlBr has the optimal combination of properties: high atomic number, high density, high mu-tau product, low Fano factor, and lower fabrication cost compared to other materials. The presence of crystal defects and ionic drift-diffusion enchained by the electric field affects the performance of today’s TlBr detectors. As a bias is applied across a detector, a defect distribution inside starts changing due to ion migration. The changes appear to be most pronounced in the first weeks of applying a bias to newly-manufactured crystals during the “conditioning” period. The 3-D position-sensitive detectors provide an opportunity to investigate these processes and their effects on the device performance and on corrections applied to the spectrum. Here, we present results from analyzing response changes in TlBr crystals under applied biases using position-sensitive capacitive Frisch-grid detectors. This work has been supported by the U.S. Department of Homeland Security, Countering Weapons of Mass Destruction Office, under competitively awarded contract 70RDND18C00000024. This support does not constitute an express or implied endorsement on the part of the Government.

Photon-Counting Detector (PCD) capable of resolving the energies of single X-ray photons is critical in medical imaging (e.g., Computed Tomography). A high count rate and negligible polarization is essential for a PCD. Besides, there has been a critical need to develop high-Z sensor for synchrotron X-ray facility. The very high X-ray fluxes (e.g., 1e6 – 1e12 photons/s/mm2) involved in both applications makes it very challenging for detector operation. Here, we demonstrate that our perovskite CsPbBr3 single crystal detectors have good performance for these applications.

High performance X-ray detectors can be realized by a variety of different approaches. However, more and more attention is paid to direct conversion X-ray detectors in a planar device geometry that use hybrid organic-inorganic perovskite semiconductors as absorber material. This study follows an alternative approach and uses a folded instead of a planar device architecture in order to realize a high performance X-ray detector. By reporting on the fabrication of a foldable perovskite sensor array and by demonstrating a high X-ray sensitivity and a high spatial resolution when the array is folded, we prove the concept of the folded perovskite detector design.

FA3Bi2I9: An emerging lead-free perovskite for radiation detection Doup Kim, Ge Yang* Department of Nuclear Engineering, North Carolina State University Ralph B. James Savannah River National Laboratory *Ge Yang (phone: 919-515-5267, email: gyang9@ncsu.edu) Abstract Semiconductor radiation detectors have been actively used in a wide range of fields including medical imaging, homeland security, environmental survey, and industrial monitoring. A series of research activities are on-going to explore new detector materials for improved performance and reduction of manufacturing costs. In this regard, perovskites have attracted strong interests in recent years. Compared with well-studied lead-based perovskite materials, lead free perovskites hold potential to enable the development of environment-friendly detector materials while providing attractive detector characteristics. Here, we report our efforts to develop an emerging perovskite material, FA3Bi2I9 (FA=CH(NH2)2) single crystals, for radiation detection. Systematic microstructural-, electrical-, optical- properties and detector tests will be presented and discussed. These results will provide fundamental knowledge regarding the potential of FA3Bi2I9 as a new class of radiation detector materials.

This presentation will review the design, optimization and construction of a new generation of compact, ultrahigh flux, narrow-bandwidth laser-Compton x-ray and gamma-ray sources and present the potential uses of these sources with respect to micron-resolution materials imaging and isotope-specific materials identification and assay based on excitation of nuclear resonance fluorescence.