This PDF file contains the front matter associated with SPIE Proceedings Volume 9968, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

In this paper we present results on a novel tin-loaded plastic scintillator. We will show that this particular plastic scintillator has a light output similar to that of BGO, a fast scintillation decay (< 10 ns), exhibits good neutron/gamma PSD with a Figure-of-Merit of 1.3 at 2.5 MeVee cut-off energy, and excellent energy resolution of about 12% (FWHM) at 662 keV. Under X-ray excitation, the radioluminescence spectrum exhibits a broad band between 350 and 500 nm peaking at 420 nm which is well-matched to bialkali photomultiplier tubes and UV-enhanced photodiodes.

A gamma-ray spectrometer for radioactive waste sorting is presented. The equipment is based on a new “thin-walled” xenon gamma-ray detector with sensitive volume of 4 liters and a digital electronics unit. Use of the thin wall (0.5 mm of stainless steel covered with fiberglass) provides lower absorption of gamma-rays by the detector’s walls and expansion of the energy range of radiation being registered. The digital electronics unit makes it possible to use the equipment in unfavorable field conditions such as high levels of acoustic influence.

We report a cost-effective and production achievable path to fabricate robust large-area microchannel plates (MCPs), which offers the new prospect for larger area MCP-based detector technologies. We used atomic Layer Deposition (ALD), a thin film growth technique, to independently adjust the desired electrical resistance and secondary electron emission (SEE) properties of low cost borosilicate glass micro-capillary arrays (MCAs). These capabilities allow a separation of the substrate material properties from the signal amplification properties. This methodology enables the functionalization of microporous, highly insulating MCA substrates to produce sturdy, large format MCPs with unique properties such as high gain (<107/MCP pair), low background noise, ~10ps time resolution, sub-micron spatial resolution and excellent stability after only a short (2-3days) scrubbing time. The ALD self-limiting growth mechanism allows atomic level control over the thickness and composition of resistive and secondary electron emission (SEE) layers that can be deposited conformally on high aspect ratio (~100) capillary glass arrays. We have developed several robust and consistent production doable ALD processes for the resistive coatings and SEE layers to give us precise control over the MCP parameters. Further, the adjustment of MCPs resistance by tailoring the ALD material composition permits the use of these MCPs at high or low temperature detector applications. Here we discuss ALD method for MCP functionalization and a variety of MCP testing results.

We studied a surface effect of Double-sided Si Strip Detectors (DSSDs) in order to apply it for imaging spectroscopy of X-ray photons down to 5 keV for the first time. The Japanese cosmic X-ray satellite Hitomi, launched in February 2016, is equipped with the Hard X-ray Imager (HXI), which employs the DSSDs in 5-80 keV. In such a low energy band, the surface effect is non-negligible. When interstrip regions of p-side are irradiated, the DSSD sometimes show signals with negative pulse heights, presumably caused by positive surface charges between Si and SiO₂ layers.1{5 The effect modifies the X-ray response of the HXI towards its low-energy end, below ~ 10 keV. By irradiating the DSSD with uncollimated mono-energetic X-rays of different energies, we measured the fraction of the negative events to be 2% at 26.4 keV and 30% at 6.0 keV. Using an 8 keV colli- mated X-ray beam, we directly verified that the negative events originated from the interstrip gaps on the p-side where the SiO₂ layers exist. The measured energy- and position- dependences can be modeled by assuming that the negative events are produced in approximately 25 μm deep and 120 μm wide interstrip regions. When the bias voltage are halved (from 350 V to 180 V), fraction of the negative events increased by a factor of ~ 1:7, qualitatively consistent with this picture.

We have analyzed the mechanisms of leakage current conduction in passivating silicon dioxide (SiO₂) films grown on (0 0 0 1) silicon (Si) face of n-type 4H-SiC (silicon carbide). It was observed that the experimentally measured gate current density in metal-oxide-silicon carbide (MOSiC) structures under positive gate bias at an oxide field Eox above 5 MV/cm is comprised of Fowler-Nordheim (FN) tunneling of electrons from the accumulated n-4H-SiC and Poole-Frenkel (PF) emission of trapped electrons from the localized neutral traps in the SiO₂ gap, IFN and IPF, respectively at temperatures between 27 and 200 °C. In MOSiC structures, PF mechanism dominates FN tunneling of electrons from the accumulation layer of n-4H-SiC due to high density (up to 10¹³ cm^-2) of carbon-related acceptor-like traps located at about 2.5 eV below the SiO₂ conduction band (CB). These current conduction mechanisms were taken into account in studying hole injection/trapping into 10 nm-thick tunnel oxide on the Si face of 4H-SiC during electron injection from n-4H-SiC under high-field electrical stress with positive bias on the heavily doped n-type polysilicon (n+-polySi) gate at a wide range of temperatures between 27 and 200 °C. Holes were generated in the n⁺-polySi anode material by the hot-electrons during their transport through thin oxide films at oxide electric fields E_ox from 5.6 to 8.0 MV/cm (prior to the intrinsic oxide breakdown field). Time-to-breakdown t_BD of the gate dielectric was found to follow reciprocal field (1/E) model irrespective of stress temperatures. Despite the significant amount of process-induced interfacial electron traps contributing to a large amount of leakage current via PF emission in thermally grown SiO₂ on the Si-face of n-4H-SiC, MOSiC devices having a 10 nm-thick SiO₂ film can be safely used in 5 V TTL logic circuits over a period of 10 years.

The ePix100A camera is a 0.5 megapixel (704 x 768 pixels) camera for low noise x-ray detection applications requiring high spatial and spectral resolution. The camera is built around a hybrid pixel detector consisting of 4 ePix100a ASICs ip-chip bonded to one sensor. The pixels are 50 μm x 50 μm (active sensor size ~ 35:4mm x 38:6 mm), with a noise of ~ 180 eV rms, a range of 100 8 keV photons, and a current frame rate of 240 Hz (with an upgrade path towards ~ 10 kHz). This performance leads to a camera combining a high dynamic range, high signal to noise ratio, high speed and excellent linearity and spectroscopic performance. While the ePix100A ASIC has been developed for pulsed source applications (e.g., free-electron lasers), it performs well with more common sources (e.g., x-ray tubes, synchrotron radiation). Several cameras have been produced and characterized and the results are reported here, along with x-ray imaging applications demonstrating the camera performance.

Microchannel Plates(MCP) have been widely used in X-ray detection, night vision and other fields. X-ray detection used in the field of space usually requires a lot of large area of MCPs. A set of multi-station electron scrubbing and performance testing device for large area MCP is developed in this paper. Four sets of large area electron source are designed for electron scrubbing. Aiming at single MCP and dual-MCP structure, the high voltage power system, signal processing module and mechanical control structure are designed to achieve scrubbing and testing of 4 groups of large area MCP at the same time. By using this device, the scrubbing and testing of large area MCPs of 106mm in diameter are achieved. The test results are given and analyzed.

We report the development of an edge termination by depositing thin Si₃N₄ passivating film on 4H-SiC epilayer based radiation detector. The edge termination method is shown to be very effective for improving both the detector leakage current and radiation detection performance compared with that of a conventional detector fabricated from the same parent wafer. The detector leakage current was found to have improved two orders of magnitude. Significant improvement in radiation detection performance was shown from alpha spectroscopy measurements prior and subsequent to Si₃N₄ edge termination. Deep Level Transient Spectroscopy (DLTS) measurements revealed a reduction in life-time killing defects of detectors with Si₃N₄ edge termination which could be related to the observed improvements in radiation detection performance.

Polyvinyltoluene-based nanocomposite plastic scintillators containing uniformly dispersed ytterbium fluoride nanoparticles are prepared by in-situ thermal polymerization. The deep-blue-emission nanocomposite monoliths are capable of producing a full energy phtotpeak when exposed to Cs-137 (662 keV) gamma radiations. The effects of monolith dimension and nanoparticles content on scintillation light yield and energy resolution are studied. A light yield of 65% (compared with the commercial standard Eljen-212) and a photopeak energy resolution of 9.2% was obtained using a sample loaded with 24.5 wt% ytterbium fluoride nanoparticles.

Lithium Indium Selenide (LiInSe₂) has been under development in RMD Inc. and Fisk University for room temperature thermal neutron detection due to a number of promising properties. The recent advances of the crystal growth, material processing, and detector fabrication technologies allowed us to fabricate large detectors with 100 mm² active area. The thermal neutron detection sensitivity and gamma rejection ratio (GRR) were comparable to ³He tube with 10 atm gas pressure at comparable dimensions. The synthesis, crystal growth, detector fabrication, and characterization are reported in this paper.

Solid-state neutron detectors with high performances are urgently sought after for the detection of fissile materials. Until now, direct-conversion neutron detectors based on semiconductors with a measureable efficiency have not been realized. We have successfully synthesized hexagonal boron nitride (h-BN) epilayers with varying thicknesses (0.3 μm – 50 μm) by metal organic chemical vapor deposition (MOCVD) on sapphire substrates. In this paper, we present the detailed characterization of thermal neutron detectors fabricated from h-BN epilayers with a thickness up to 5 m to obtain insights into the h-BN epilayer thickness dependence of the device performance. The results revealed that the charge collection efficiency is almost independent of the h-BN epilayer thickness. By minimizing h-BN material removal by dry etching, it was shown that detectors incorporating an isotopically ¹⁰B-enriched h-BN epilayer of 2.7 μm in thickness exhibited an overall detection efficiency for thermal neutrons of 4% and a charge collection efficiency as high as 83%. By doing away altogether with dry etching, we have successfully realized a simple vertical 43 μm thick h-¹⁰BN detector which delivers a detection efficiency of 51.4% for thermal neutrons, which is the highest reported efficiency for any semiconductor-based neutron detector The h-BN detectors possess all the advantages of semiconductor devices including low cost, high efficiency and sensitivity, wafer-scale processing, compact size, light weight, and ability to integrate with other functional devices.

CMOS pixel electronics open up for applications with single photon or particle processing. TIMEPIX3 is a readout chip in the MEDIPIX family with the ability to simultaneously determine energy and time of interaction in the pixel. The device is fully event driven, sending out data on each interaction at a maximum speed of about 40 Mhits/s. The concept allows for off-line processing to correct for charge sharing or to find the interaction point in multi pixel events. The timing resolution of 1.56 ns allows for three dimensional tracking of charged particles in a thick sensor due to the drift time for the charge in the sensor. The experiments in this presentation have been performed with silicon sensors bonded MEDIPIX family chips with special focus on TIMEPIX3. This presentation covers basic performance of the chip, spectral imaging with hard X-rays, detection and imaging with charged particles and neutrons. Cluster identification, centroiding and charge summing is extensively used to determine energy and position of the interaction. For neutron applications a converter layer was placed on top of the sensor.

The Silicon Geiger Hybrid Tube (SiGHT) is a novel photosensor designed for future generations of rare event search experiments using noble liquids. The main idea is to replace conventional multi-dynode photomultiplier tubes (PMTs) with a hybrid technology, consisting of a low temperature sensitive bialkali photocathode for conversion of photons into photoelectrons and a low dark count silicon photomultiplier (SiPM) for photoelectron signal amplification. SiGHT can achieve ultra low internal radioactivity, high quantum efficiency and stable performance at low temperatures, which are required features for rare event searches such as direct dark matter detection and neutrinoless double beta decay experiments. The first SiGHT prototype fabrication is in progress at UCLA. The current status of the development is presented.

Xenon gamma-ray spectrometer for monitoring of 222Rn concentration by means of measurement of its daughter nuclei gamma-ray emission intensity and the main characteristics of this device are presented. Time variations of radon concentration can be interpreted as possible precursors of the Earth’s seismic activity, such as an earthquake, several days prior to these events. The results of the first experiments that were carried out in the Caucasus region of Russia show the possibility of using the described xenon gamma-ray spectrometer for this task.

We report pilot production and advanced development performance results achieved for Large Area Picosecond Photodetectors (LAPPD). The LAPPD is a microchannel plate (MCP) based photodetector, capable of imaging with single-photon sensitivity at high spatial and temporal resolutions in a hermetic package with an active area of 400 square centimeters. In December 2015, Incom Inc. completed installation of equipment and facilities for demonstration of early stage pilot production of LAPPD. Initial fabrication trials commenced in January 2016. The “baseline” LAPPD employs an all-glass hermetic package with top and bottom plates and sidewalls made of borosilicate float glass. Signals are generated by a bi-alkali Na₂KSb photocathode and amplified with a stacked chevron pair of “next generation” MCPs produced by applying resistive and emissive atomic layer deposition coatings to borosilicate glass capillary array (GCA) substrates. Signals are collected on RF strip-line anodes applied to the bottom plates which exit the detector via pinfree hermetic seals under the side walls. Prior tests show that LAPPDs have electron gains greater than 107, submillimeter space resolution for large pulses and several mm for single photons, time resolutions of 50 picoseconds for single photons, predicted resolution of less than 5 picoseconds for large pulses, high stability versus charge extraction, and good uniformity. LAPPD performance results for product produced during the first half of 2016 will be reviewed. Recent advances in the development of LAPPD will also be reviewed, as the baseline design is adapted to meet the requirements for a wide range of emerging application. These include a novel ceramic package design, ALD coated MCPs optimized to have a low temperature coefficient of resistance (TCR) and further advances to adapt the LAPPD for cryogenic applications using Liquid Argon (LAr). These developments will meet the needs for DOE-supported RD for the Deep Underground Neutrino Experiment (DUNE), nuclear physics applications such as EIC, medical, homeland security and astronomical applications for direct and indirect photon detection.

Cs₂HfCl₆ (CHC) is one of the most promising recently discovered new inorganic single crystal scintillator that has high light output, non-hygroscopic, no self-activity, having energy resolution significantly better than NaI(Tl), even approaching that of LaBr3 yet can also potentially be at a much lower cost than LaBr3. This study attempts to use Monte Carlo simulation to examine the great potential offered by this new scintillator. CHC’s detector performance is compared via simulation with that of 4 typical existing scintillators of the same size and same PMT readout. Two halide-scintillators: NaI(Tl) and LaBr3 and two oxide-scintillators: GSO and LSO were used in this simulation to compare their 122 keV and 511 keV gamma responses with that of CHC with both spectroscopy application and imaging applications in mind. Initial simulation results are very promising and consistent with reported experimental measurements. Beside detector energy resolution, image-quality measurement parameters commonly used to characterize imaging detectors as in nuclear medicine such as Light Response Function (LRF) which goes in parallel with spatial resolution and simulated position spectra will also be presented and discussed.

Pixelated Cadmium Zinc Telluride (CZT) detectors provide the opportunity to perform spectroscopic imaging for discriminating one radioactive material from another. Although Compton interactions provide a means for imaging high energy gamma sources, identification of materials emitting lower energy signatures are better suited to collimator imaging techniques. This paper specifically considers a multiple pinhole method for its simplicity of pinhole focusing combined with straightforward processing methods for incorporating multiple apertures to reduce photon collection time while retaining image resolution. Multiple pinhole image detections are combined using an iterative Maximum- Likelihood Expectation-Maximization (MLEM) synthetic imaging algorithm. To enable subsequent field operations, the imaging system matrix is computed using an imaging model with adjustable parameters rather than one experimentally acquired from point sources. The system model includes an object space, a multiple pinhole collimator plane, and a pixelated detection plane. The modeled object space is implemented in two dimensions to reduce image reconstruction burden since 3D imaging is not practical for single view stand-off imaging. Focusing is modeled by a function computing photon trajectory and passage through the pinhole patterned barrier plane. Results show that a MLEM processed image will achieve resolution approaching that of a single pinhole imaged onto the full detector. The multiple pinhole advantages of simple implementation with shorter focal lengths combined with the availability of portable CZT detectors would be useful in short stand-off applications. Work is currently in progress to experimentally quantify spatial resolution and imaging timelines using an eV Products D-Matrix 4x4 array of pixelated CZT modules.

The temperature gradient at the growth interface is as important as the growth temperature and the growth rate for growing CdTe single crystals by the Traveling Heater Method (THM). This article presents the results of an experimental study of the influence of the growth temperature gradient on THM growth of CdTe single crystals. CdTe crystals were grown at about 900°C with the growth rate of 10 mm/day and the rotation rate of 3 rpm. With the growth temperature gradient of about 30 °C/cm even a single-grain structure became a multi-grain structure in the final stage of growth. On the other hand, with the growth temperature gradient of about 50 °C/cm, even if the crystal started with multi-grains, it became a single crystal eventually. The constitutional supercooling criterion was used to interpret these results.

Cadmium Zine Telluride (CZT) has been extensively studied as a room temperature semiconductor gamma radiation detector. CZT continues to show promise as a bulk and pixelated gamma spectrometer with less than one percent energy resolution; however the fabrication costs are high. Improved yields of high quality, large CZT spectroscopy grade crystals must be achieved. CZT is grown by the Traveling Heater Method (THM) with a Te overpressure to account for vaporization losses. This procedure creates Te rich zones. During growth, boules will often cleave limiting the number of harvestable crystals. As a result, crystal growth parameter optimization was evaluated by modeling the heat flow within the system. Interestingly, Cadmium Telluride (CdTe) is used as a thermal conductivity surrogate in the absence of a thorough study of the CZT thermal properties. The current study has measured the thermal conductivity of CZT pressed powders with varying Te concentrations from 50-100% over 25-800°C to understand the variation in this parameter from CdTe. Cd0.9Zn0.1Te1.0 is the base CZT (designated 50%). CZT exhibits a thermal conductivity of nearly 1 W/mK, an order of magnitude greater than CdTe. Further, the thermal conductivity decreased with increasing Te concentration.

Photon detection is a central element of any high-energy astronomy instrumentation. One classical setup that has proven successful in many missions is the combination of photomultiplier tubes (PMTs) with scintillators, converting incoming high-energy photons into visible light, which in turn is converted in an electrical impulse. Although being extremely sensitive and rapid, PMTs have the drawback of being bulky, fragile, and require a high-voltage power supply of up to several thousand volts. Recent technological advances in the development of silicon photomultipliers (SiPM) make them a promising alternative to PMTs in essentially all their applications. We have started a RD program to assess the possibility of using SiPMs for space-based applications in the domain of high-energy astronomy. We will present results of our characterization studies of SiPMs from 3 manufacturers. Each SiPM detector has been tested inside a dedicated vacuum chamber and at low temperature to assess its performance in a representative space environment. Irradiation tests are scheduled to understand the susceptibility of SiPM to radiation damage. After comparison, we will select a baseline detector and design a specific front-end electronics and mechanical system. Furthermore, we plan to develop a low noise voltage power supply that ensures the stability of the SiPMs and to study their coupling to scintillators. Finally, our ultimate goal is to qualify the system for a space Technical Readiness Level of 5.

The spatial resolution of scintillator type imaging detector is not so high because diffusion of luminescence in the scintillator. As a countermeasure, the silicon substrate was processed to make a small grid by MEMS technique for optical separation of scintillator. The silicon grid wall can completely obtain optical-separation for visible light as a result of X-ray scintillation. Moreover, we can get large-size silicon wafers up to diameter of 30cm with high precision semiconductor process. In this paper, the purpose is to fill a scintillator material such as CsI:Tl, inside of the grid substrate. Because the aspect ratio of the grid is large (90μm x 90μm with 800μm depth), it is not easy to fill scintillator inside the grid. Moreover, it is necessary to ensure uniformity, intention of light emission. In this study, the CsI:Tl was filled inside of the grid by resistive heated evaporation method. We evaluated by X-ray luminescence and test chart.