This PDF file contains the front matter associated with SPIE Proceedings Volume 12241 including the Title Page, Copywrite information, and Table of Contents.

Existing COTS inorganic scintillators all have the characteristic of being very good at certain desirable properties, but not sufficient at other desirable properties for HEP. The demand for suitable scintillators (with regards to both scintillation detector properties and suitable pricing), to be used for modern intensities frontier (Mu2e-II), energy frontier (High luminosity large hadron collider) and future e+e- collider projects (aimed as Higgs bosons factory, such as the International Linear Collider (ILC) and the Future Circular Collider (FCC) are putting even higher challenges on crystal scintillators. In this work, we report the development of a novel high-performance scintillators that can address the issues associated with existing scintillators, the activator doped Hg2Br2. Initial results are very encouraging on the detection of gamma and alpha particles using a solid-state photomultiplier (SSPM). The responses have been stable and repeatable. Hg2Br2 also has many advantages over existing COTS scintillators such as: high density, bright, fast, good energy resolution, no intrinsic radiation, radiation hard and cost-effectiveness. We present here why Hg2Br2 is the next generation scintillator for high energy physics experiments as well as other scientific and imaging applications such as planetary science and medical imaging.

Scintillation mechanisms in inorganic scintillators were reviewed and reorganized in a more comprehensive way, from excitonic to activator-based, charge transfer luminescence, to Auger-free core-valance luminescence as well as selfactivation and donor-acceptor recombination. The focus is on excitonic mechanisms since this is the class with many subcategories (free exciton, self-trapped exciton (STE), exciton bounds to donor/acceptor/trapping centers…) that published articles fail to cover the most, despite the fact that excitonic mechanism tends to be the dominant mechanism in ultra-fast semiconductor scintillators highly sought-after nowadays as in ZnO. Focus will also be on alkali halide scintillators such as NaI(Tl) and CsI(Tl), both doped and undoped since they are still referenced standards despite having 70 years in the making. The review is unique in the sense that its purpose is to clarify and enrich existing literatures and hence provide a more comprehensive collection of inorganic scintillation mechanisms known to date. Despite the focuses, the reorganized classification was attempted to cover all classes of inorganic scintillators include various forms of halides to oxides, chalcogenides and the more recent trend in nanocomposite ceramic scintillators. Topics such as STE, color centers and general exciton dynamics will be presented more in-depth.

A defunct technology of lead tungstate (PbWO4, PWO) crystal growth was re-established and improved at Crytur. It has been discovered that key to crystal quality is pretreatment of raw material and double crystallization, although time consuming, but very effective in optimizing the final product. Several important technological advances have been made to be able to industrialize and scale up the crystal production for the needs of the large-scale physics experiments. These crystals have been evaluated at the Jefferson Accelerator facility in Newport News, VA, and found to meet the stringent requirements of the future detectors for EIC, unlike PWO crystals grown by different methods by other suppliers. Comparison of the crystal performance conducted by JLAB will be shown.

Transparent ceramic Cerium-doped Gadolinium Yttrium Gallium Aluminum Garnet, GYGAG(Ce), offers a combination of environmental stability, high light yield, good gamma spectroscopy and formability into large plates that is attractive for implementation into Radiation Portal Monitors. GYGAG(Ce) plates at 4” x 4” x 0.5” scale achieve energy resolution of R(662 keV) <7%. Production of high transparency 8 in³ GYGAG(Ce) plates is underway, as well as their integration into detector modules and portal systems.

Thallium bromide (TlBr) is a promising material for room temperature gamma radiation detection due to its high density, high atomic number, and wide bandgap. Additionally, TlBr has a cubic crystal structure and melts congruently at a relatively low temperature. Advances in material purification, crystal growth and device processing have led to improved material quality including a significant increase in the mobility-lifetime product of electrons in TlBr. This has enabled single carrier collection devices with thicknesses of 1 cm and beyond. The arrays have been flip-chip bonded to carrier boards using a low temperature curing conductive polymer. In this paper we report on results from planar and pixelated devices. Planar TlBr devices with dimensions of 12 mm × 12 mm × 7 mm exhibit an energy resolution ranging from 3% to 5% FWHM at 662 keV when using a shaping time of 2 s. The energy resolution in planar devices improves with a reduction of the shaping timing consistent with the expected amelioration of the depth dependence. The 1-cm thick pixelated arrays, with a pitch of 1.72 mm, produce an energy resolution in the anode spectrum ranging from 1.8% to 4.4%, without applying depth corrections. This work presents spectra from a selected pixel for ¹³³Ba and ⁵⁷Co irradiation. Measurements of the room-temperature stability of the planar and pixelated detectors show that the position of the 662-keV photopeak is stable over a period of ~200 days, but the shape of the photopeak in the anode spectra exhibits small changes. These detectors show promise for applications in radio-isotope identification devices and for medical imaging.

Ni/Y₂O₃/4H-SiC metal-oxide-semiconductor (MOS) structure has been realized on 20 μm thick 4H-SiC epitaxial layers by depositing 40 nm thick Y₂O₃ layers through pulsed laser deposition and using nickel as the gate contact. 4H-SiC based MOS structures with thin oxide layers are being considered as novel detector structures for ionizing radiation. Y₂O₃ being a wide bandgap (5.5 eV) and high-𝑘 dielectric (𝑘 = 14-16) is beneficial to lower the junction leakage current and increasing the bias voltage limit. The current-voltage (I-V) characteristics recorded for the fabricated MOS devices revealed excellent rectification properties and a very low leakage current density of 80 pA/cm² at a gate bias of -500 V. The Mott-Schottky plot obtained from high frequency (1 MHz) capacitance-voltage (C-V) measurement revealed a linear trend as observed in Ni/4H-SiC Schottky barrier detectors. A built-in potential of ≈2.0 V has been calculated from the C-V characteristics. The radiation detection properties of the MOS detectors have been assessed through pulse height spectroscopy using a ²⁴¹Am alpha particle source. The detectors revealed a well-defined peak in the pulse height spectrum with an energy resolution of 1.6% and a charge collection efficiency (CCE) of 82% at 0 V applied bias (self-biased mode) for the 5486 keV alpha particles. The energy resolution and the charge collection efficiency were seen to improve further with increased gate bias. A CCE of 1.0 and an energy resolution of 0.4% has been observed when the MOS detector was biased at -50 V. A very long hole diffusion length of 56 μm has been calculated using a drift-diffusion model and the variation of experimentally obtained CCE with bias voltage. Such long hole diffusion length and the high built-in potential has led to the highefficiency detection performance in self-biased mode. Capacitance-mode deep level transient spectroscopy revealed the presence of deep level trap centers commonly observed in 4H-SiC epilayers with trap concentrations similar to that has been observed in our previous devices.

Li-based semiconductor materials represent a promising alternative to 3-He and scintillation materials for thermal neutron detection and imaging instruments. Semiconductor crystals of LiInSe₂, LiInP₂Se₆, and LiGaInSe₂ (LiGa_0.5In_0.5Se₂) were grown using natural and enriched lithium (⁶Li). The materials were characterized for electronic and optical properties including optical transmission, current-voltage (I-V) characteristic for resistivity, and bandgap. Thermal neutron detectors were fabricated and characterized for neutron and gamma-ray response. Pulse height spectra were collected from a moderated custom-designed ²⁴¹AmBe neutron source and a ⁶⁰Co gamma-ray source. The LiInSe₂ samples exhibited a 2.8 eV cutoff in the optical spectrum and a resistivity of ~8×10¹¹ Ω·cm. LiInSe₂ devices exhibit a noise floor of <30 keV which operated at a field of 630 V/mm, for the 0.8-mm thick device. The Vertical Gradient Freeze (VGF) grown LiInP₂Se₆ samples exhibited a 2.2 eV cutoff in the optical spectrum and resistivity of ~4×10¹² Ω·cm. The Chemical Vapor Transport (CVT) grown LiInP2Se6 devices exhibit a noise floor of <60 keV which operated at a field of 8,000 V/mm, for the 0.05- mm thick device. Furthermore, the long-term stability of LiInSe₂ devices during multiple weeks under continuous bias was investigated.

Commercial and laboratory neutron detection systems use indirect neutron response of materials like pressurized helium-3 (via nuclear reaction ³He(n, p)³H) to measure and count neutrons emanating from a source. Recently a host of semiconductors, especially a ternary semiconductor of lithium indium diselenide (⁶LiInSe₂) and a quaternary alloy of enriched lithium-6, indium, phosphorous, and selenium (⁶LiInP₂Se₆), have shown promising neutron counting possibilities by directly converting neutrons into charge-carrying elements within the body of the semiconductor. These semiconductors have high thermal neutron capture cross sections, suitable energy bandgaps (~2.0 electron volts) for room-temperature operations, and a favorable electronic band structure for efficient electron charge transport. The article examines the semiconductor properties of these compounds in terms of their neutron counting capabilities and possible ways to extract neutron energy information from them. Lithium-6 and boron-10 (with thermal neutron absorption cross sections of 938 ± 6 and 3855 ± 26 barns, respectively) produce charged particles to be measured via indirect neutron interactions. The efficiency of indirect conversion neutron detectors is limited because of the inefficiencies in conversion mechanism. In case of direct conversion, the neutrons create charged particles in a single material for neutron capture and charge collection, increasing detection efficiency. Unlike ³He proportional counters, which provide no neutron energy information, the semiconductors can be used as neutron energy spectrometer. Fully resolved neutron energy by ⁶LiInP₂Se₆ from a plutonium-beryllium source has been reported in the literature. We will discuss the influence of these multilayered semiconductors’ crystallographic structures and growth techniques on neutron energy determination.

A composite fast neutron detector module based on the ⁶Li(n,α) ³H reaction in ⁶Li-enriched GS20® scintillating glass has been engineered to be compact, robust, and tunable. The solid scintillating composite consists of only three components, all commercially sourced, and can be optically coupled to silicon photomultipliers (SiPMs) to create a highly capable and portable neutron detector module. The composite provides moderation of incident fast neutrons through an optically transparent organic matrix and achieves high gamma rejection by the use of small scintillating particles. The performance of the module was assessed by measurements of the die-away time and the sensitivity to both gammas and neutrons. Controlled scintillation light losses enable determination of the neutron capture location along the length of the cylindrical composite. Optical raytracing was used to predict the light-transport efficiencies and the longitudinal position dependency of scintillation events within the module. These assessments indicate that this module can be effective in the detection of nuclear material for nonproliferation, safeguards and security applications, and in fundamental and applied science.

Radionuclide Identification Devices (RIDs) or Backpack Radiation Detection Systems (BRDs) are often equipped with NaI(Tl) detectors. We demonstrate that such instruments could be provided with reasonable thermal- and fast-neutron sensitivity by means of an improved and sophisticated processing of the digitized detector signals: Fast neutrons produce nuclear recoils in the scintillation crystal. Corresponding signals are detectible and can be distinguished from that of electronic interactions by pulse-shape discrimination (PSD) techniques as used in experiments searching for weakly interacting massive particles (WIMPs). Thermal neutrons are often captured in iodine nuclei of the scintillator. The gamma-ray cascades following such captures comprise a sum energy of almost 7 MeV, and some of them involve isomeric states leading to delayed gamma emissions. Both features can be used to distinguish corresponding detector signals from responses to ambient gamma radiation. The experimental proof was adduced by offline analyses of pulse records taken with a commercial RID. An implementation of such techniques in commercial RIDs is feasible.

Nuclear material assay is fundamental to missions like materials control and accountability, nuclear counter terrorism, or treaty verification. Neutrons from fission chains get detected in bursts separated by gaps. This pattern in time of neutron arrivals provides information about the quantity and arrangement of the nuclear materials. In a weapon, hydrogenous materials often surround the nuclear materials, meaning both fast- and thermal-neutrons come out. When neutrons get absorbed, gamma-rays with the parent neutron’s timing emerge. Our missions would be significantly easier with scintillators to detect all three species with nanosecond timing and at least moderate energy resolution for the gammas.

Neutron radiography and computed tomography may be used to investigate internal structures of complex multi-material objects nondestructively. Thermal neutrons are more effective at producing high-contrast radiographs of objects composed of elements with relatively low atomic numbers (Z). A capability to produce high-quality CT reconstructions from both thermal and fast neutron computed tomography (nCT) using a lens-coupled imaging was demonstrated using various Additively Manufactured (AM’d) and Electrical Discharge Machining (EDM) phantoms, with layers and distinct features, made with intentional voids and out of high- and low-Z elements.

X-ray computed tomography (CT)systems can produce high resolution images, in which small (sub-millimeter) features can be detected. This requires the X-rays to sufficiently penetrate the object and interact strongly enough to produce measurable attenuation. Low atomic number (low Z), low density objects shielded by high atomic number (high Z) materials result in X-ray reconstructions that lack sufficient contrast to differentiate interior features from noise and reconstruction artifacts. Fast neutron CT offers complementary information to X-rays with superior penetration through high Z shielding and with less severe beam hardening artifacts. However, spatial resolution in X-ray imaging systems is generally superior to that of fast neutron imagers. Here, we quantitatively compare these two complementary modalities to demonstrate the ability to observe small feature locations within two multi-material objects. Quantitative measures include calculation of image gradient at material edges, contrast-to-noise ratio, and F1 score.

When a high-intensity laser (I_L ≥ 10¹⁸ W/cm² ) strikes a solid target, the laser ionizes the material and couples its energy to the so-called hot electrons. Hard X-rays are subsequently emitted from the laser-target interaction mainly in a form of the braking (bremsstrahlung) radiation owing to the electrons scattering in the ions Coulomb field. Measurement and characterization of such photons are of strong interest since it can provide resourceful information about inner plasma processes (i.e. laser absorption, heat transfer) and help to determine key properties of other plasma byproducts (i.e. temperature, acceleration method). Here we present results obtained using a scintillator-array based calorimeter at ELI-Beamlines (Extreme Light Infrastructure) during the ELIMAIA user beamline (ELI Multidisciplinary Applications of laser-Ion Acceleration) commissioning, where a PW laser with intensities up to I_L =10²¹ W/cm² was applied on thin (µm) solid targets. The detector consists of scintillator prisms of different thicknesses and materials (plastic EJ200 and BGO) read out by a CMOS camera and aims at the radiation temperature retrieval. Characterization of the hard X-rays measured from the laser interaction with Ni target is summarized in this work. The stability of the measured radiation temperature is demonstrated.

Understanding the underlying physics governing astrophysical jets associated with Gamma-Ray Bursts (GRBs) is necessary to advance the field of gamma-ray astronomy. Existing physics models can be constrained through GRB polarization studies. The Gamma-Ray Polarimeter Experiment (GRAPE) is a high-altitude balloon experiment designed to measure GRB polarization over the energy range of 50-500 keV at flight altitudes. A flight of the newest GRAPE design is scheduled to fly from Fort Sumner, NM in August 2023. The new design is based on an arrangement of small scintillation detector elements designed to measure photon interactions in three dimensions and provide modest imaging capabilities. The flight instrument consists of a 3-dimensional (7x7x5) array of high-Z (GAGG) and low-Z (P-terphenyl) scintillators each read out by individual Hamamtsu MultiPixel Photon Counters (MPPCs). Previous GRAPE missions have been sensitive to M-class solar flares and observations of the Crab Nebula with low signal to background ratios. The new design improves performance relative to the previous GRAPE design through the use of advanced scintillator materials, the ability to perform modest Compton imaging for source localization and background rejection, and by completely eliminating optical cross-talk. Background reduction is achieved using the imaging capabilities allowing for some level of event rejection for events inconsistent with the source direction. This paper will present the new module design and simulated response parameters to provide an estimate of the balloon payload sensitivity.

By combining radiation detection technologies with robotics sensing, the ability to continuously conduct gamma-ray imaging using freely-moving systems was demonstrated in 2015.¹ This new method, which was named free-moving 3D Scene Data Fusion (SDF), was then applied to mapping radioactive contamination and to contextualizing the extent of contamination and the efficacy of radiological clean-up efforts.^{2, 3} Since then, further studies into the types of radiation detection systems to which SDF could be applied resulted in the discovery and demonstration that neutron activity could be mapped using neutron-sensitive CLLBC scintillators, arrays of pixelated CZT detectors could be used to create multi-modal imagers, and more rudimentary detector systems such as arrays of four CsI modules could still achieve good-quality mapping by inferring source positioning through the encoded modulation of source-to-detector distance. This paper provides an overview of the SDF technology, highlights recent measurements leveraging SDF-equipped systems, discusses the continued development of quantitative algorithms^{4, 5} and their ramifications for developing autonomous SDF-capabilities, and summarizes future directions of research and application development for free moving radiation detection systems.

The alpha emitting actinide ²⁴¹Am is electrodeposited on the surface of the Pt electrode of in-house fabricated SiC Schottky diodes. With 17 nCi ²⁴¹Am directly coated on the top of a device, the 2-pi geometry yields a high energy (5.486 MeV) and a long-term irradiation accumulating to a high fluence (1.6 × 10⁹ alpha particles’ infusion/month). The forward, reverse I/V, and dark current, are periodically measured to monitor key characteristics of device durability for any sign of degradation over time. The direct deposition of actinides on the surface of the device also enables the evaluation of radiation damage through alpha particles’ energy spectroscopic performance, which shows a clear spectrum degradation that can be reversed by optical excitation of the device prior to spectrum acquisition. As an analytical aide, the device performance is also simulated by Allpix² . This study provides an insight into the durability of 4H-SiC as an energy converter option for alpha-voltaic batteries and the survivability in the other harsh environment found in nuclear fuel cycle, high energy physics, fission, fusion, and space exploration where rad-hard sensors are required.

The usefulness of GYGAG(Ce) transparent polycrystalline ceramic garnet scintillators as the conversion medium in alpha and beta-fueled radioisotope batteries was explored through 0.5 to 3.5 MeV helium ion, alpha, and 0.5-2 MeV electron irradiations. Absorption spectra and light yields were measured before and after irradiations. Within experimental error no degradation in light yield was observed for the electron-irradiated samples as measured via beta or gamma excitation. A small increase in optical absorption near the emission wavelength was observed following the largest dose electron irradiation. Significant reduction in light yield was observed following helium ion irradiation. Partial recovery of the light yield was observed following annealing in oxygen above 400oC for helium ion irradiated samples. These results suggest that GYGAG(Ce) may prove useful for beta-fueled scintillation-based radioisotope batteries by allowing for higher energy beta emitters, increased power densities, and long service lifetimes.

This study describes the application development of multiple-input multiple-output radios to provide persistent mobile ad hoc network (MANET) for the Department of Homeland Security. By using Man Portable Unit (MPU5) fifth generation radios (manufactured by Persistent Systems) with the Android Team Awareness Kit (ATAK), an Android smartphone geospatial infrastructure and military situational awareness application, the Remote Sensing Laboratory has developed a MANET connectivity to monitor deployed nuclear/radiological search operation assets. Network-capable radiation monitoring systems such as backpacks, vehicle-mounted sensors, and high-resolution high-purity germanium (HPGe) detectors have been integrated to facilitate surveillance operations, routine maintenance and status of health checks, radiation alerts and alarm monitoring, and adjudication. This network connectivity application is particularly useful for maritime search operations. Shipboard search is conducted with backpack detectors and long dwell detector systems. Search techniques that involve the use of spectral anomaly detection algorithms applied to data from low-resolution gamma detectors, as well as the use of spatial interpolation tools, provide higher sensitivity to masked sources that may elude basic gross-count-rate-based algorithms. Small-vessel search techniques involve mounting large-volume mobile detectors on small boats and operating them in the same way as land-based mobile detection systems (i.e., searching for radiological/nuclear signatures emanating from nearby vessels or from targets on the water or shore). Data communication is difficult in a maritime environment because satellite communications may not be steady and multi-hop wireless networks with stations having backhaul infrastructure along coastlines may not be available. The MANET structure described in this study resolves data loss and network latency issues associated with maritime search operations.

Electro-physical properties of Cr/Hg₂MnInTe⁶/In photosensors with a surface nanostructure (SNS) created by a special surface treatment were measured in this work. With this treatment, the surface lost its mirror-like shine and was perceived as matte. For comparison, the fabrication of a Au/Hg₂MnInTe₆/In structure on a mirror surface was also performed. Hg₂MnInTe₆ single crystals were grown by modified zone melting and have an electronic type of conductivity with a band gap equal to E_g=1.21 eV and a high resistivity ρ≈2·10⁷ Ω×cm (at 293 K), which was determined from the linear section of the I-V curves. The initial section of the I-V curve for Cr/Hg₂MnInTe₆/In at reverse bias (0.1 – 10 V) could be described within the framework of the Sah-Noys-Shockley model. At voltages greater than 10 V, a linear dependence of the I-V curve was observed, and at voltages greater than 200 V, currents limited by space charge (CLSC) were observed. Cr/Hg₂MnInTe₆/In photosensors with SNS (matte surface) had significantly better electro-physical parameters than Au/Hg₂MnInTe₆/In photosensors (mirror surface): smaller dark currents, higher rectification coefficient, and higher current monochromatic sensitivity. For example, at 1 V, the dark current for Au/MMIT/In is equal to I=29 nA, and for Cr/MMIT/In, the dark current is I=2 nA. At a voltage of U=10 V, the dark currents are 150 nA and 7 nA, respectively. The rectification coefficient for Cr/Hg₂MnInTe₆/In at 10 V was К≈40, and for Au/Hg₂MnInTe₆/In it was К≈7. Due to the surface treatment before depositing rectifying contacts, the current monochromatic sensitivity S_&lambda; for structures of Cr/Hg₂MnInTe₆/In reached a maximum at a wavelength of λ≈1.15 μm and was equal to S_&lambda;≈3 A/W, and for Au/Hg₂MnInTe₆/In the sensitivity S_&lambda;≈0.8 A/W.

The In/CdTe/Au p-n junction-diode X/γ-ray detectors, formed by frontside laser irradiation doping, were studied using IV characteristics, measured at different temperatures, and spectra of ²⁴¹Am, ⁵⁷Cs, and ¹³⁷Cs isotopes, obtained in a wide bias range V = 60-380 V. A key feature of the technology was low-temperature ( ~90 ºC) vacuum annealing of polished in a Br-methanol solution detector-grade (111) oriented p-like CdTe crystals prior to the deposition of an In dopant film and formation of electrodes. After laser-induced doping of a layer near the In/CdTe interface and deposition of an Au electrode (ohmic contact), the In/CdTe/Au structures showed high rectification. The I-V measurements and calculations revealed that the dominant charge transport mechanism at low reverse bias was generation-recombination in the space charge region. It was noteworthy that the reverse current linearly increased at higher V ≥ 50 V when the depletion region extended over the entire crystal thickness. A sharp increase in I at higher V, that was inherent in diode structures (I ~ V n , n < 1), was not observed that evidenced a perfect ohmic contact, i.e. no injection of minority carriers from the Au/CdTe contact occurred. The detectors formed on the preliminary annealed CdTe crystals showed high energy resolution ((FWHM = 0.99 %@662keV at V = 300 V). Furthermore, high spectroscopic characteristics (detection efficiency, energy resolution, true energy position of the 662 keV peak) were observed (with a deviation < 20 %) at V =150-400V.

The electrical and spectroscopic characteristics of the ionizing radiation detectors, designed as Ti/CdTe/Au diodes with a rectifying barrier were investigated. Schottky (Ti/CdTe) and ohmic (Au/CdTe) contacts were formed on the B- and Afaces of detector-grade p-CdTe(111) crystals subjected to Ar plasma treatment. Owing to the advantages of the fabrication technique, the Ti/CdTe/Au Schottky-diode X/γ-ray detectors with similar parameters were obtained. The features of the single detector and stacks of two mounted detectors, connected in parallel or series, were analyzed. The measurements of the I-V characteristics showed that the sensor, consisting of two series-connected detectors, has lower dark current and significantly the weakened effect of space-charge-limited currents (SCLC) than the single detector or two parallel-connected detectors. The stack of the detectors connected in parallel has higher photosensitivity but lower energy resolution compared with those characteristics of the single detector. The analysis of the emission spectra of 137Cs and 241Am isotopes, measured at room temperature, showed that the sensitivity of the stack of the series-connected detectors turned out to be the highest. However, the double peaks were observed in the isotope spectra taken with such detector stack that was unusual and attributed to features of the electronic signal processing. Series connection of detectors has the advantages as reducing the dark current and decreasing the stack capacitance. To implement these features and optimally use such connection, specific electronic devices are needed, in particular to combine two charge packets which are formed by the detector stack into one with a larger amplitude.