Breakthrough energy resolution, R(662keV) <4%, has been achieved with an oxide scintillator, Cerium-doped Gadolinium Yttrium Gallium Aluminum Garnet, or GYGAG(Ce), by optimizing fabrication conditions. Here we describe the dependence of scintillation light yield and energy resolution on several variables: (1) Stoichiometry, in particular Gd/Y and Ga/Al ratios which modify the bandgap energy, (2) Processing methods, including vacuum vs. oxygen sintering, and (3) Trace co-dopants that influence the formation of Ce4+ and modify the intra-bandgap trap distribution. To learn about how chemical composition influences the scintillation properties of transparent ceramic garnet scintillators, we have measured: scintillation decay component amplitudes; intensity and duration of afterglow; thermoluminescence glow curve peak positions and amplitudes; integrated light yield; light yield non-proportionality, as measured in the Scintillator Light Yield Non-Proportionality Characterization Instrument (SLYNCI); and energy resolution for gamma spectroscopy. Optimized GYGAG(Ce) provides R(662 keV) =3.0%, for 0.05 cm3 size ceramics with Silicon photodiode readout, and R(662 keV) =4.6%, at 2 in3 size with PMT readout.

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.

The scintillators currently providing the best energy resolution lower than 2.6% at 662 keV and sizes larger than 1 in. dia. 1 in. height are LaBr3(Ce) and SrI2(Eu). Despite energy resolution and decay time performance of LaBr3(Ce), the intrinsic radioactivity, due to naturally occurring 138La isotope in the matrix is a limitation for low count rate applications such as radioisotope identification of weak sources. Cesium Hafnium Chloride (CHC) is a high effective atomic number (Zeff=58) moderate density (3.86 g/cm3) scintillator for gamma spectroscopy, offering a cubic crystal structure, no intrinsic radioactivity, and highly proportional light yield, without intentional doping. CHC boasts a cubic crystal structure that is isostructural to K2HfCl6 and analogous to calcium fluoride with cesium ions in the fluorine ion position and the [HfCl6]2- octahedral replacing calcium ions. The scintillation of CHC is centered at 400 nm, with a principal decay time of 4.37 s, a light yield of up to 54,000 photons/MeV and energy resolution of 3.3% at 662 keV and we report on the effects of doping on the scintillation properties of CHC.

The self-activated novel scintillating material, Cs2LiCeCl6, was grown and evaluated at BNL for dual gamma and thermal-neutron detector applications. Cs2LiCeCl6 belongs to the elpasolite family. Because of its cubic structure, Cs2LiCeCl6 has good potential for growth of large-volume ingots. The emission spectra showed doublet emission bands peaking at 384 nm and 402 nm, similar to CLYC. An energy resolution of ~ 6% at 662 keV was measured. Thermal neutrons were also detected with a resolution of ~ 4%. Results on the grown ingots using natural Li and enriched 6Li source materials will be presented and discussed.

Non-stoichiometry related extended defects in CdTe/CZT, such as tellurium inclusions and precipitates are known to be detrimental bulk defects in detector grade cadmium zinc telluride. In our attempt to minimize the size of tellurium inclusions we have employed accelerated crucible rotation technique in modified vertical Bridgman growth configuration. Acceleration and deceleration rate as high as 900 rpm2 was successfully applied during superheated melt mixing and growth. By comparing growths with and without ACRT under otherwise identical growth conditions, it was observed that the average inclusion size reduced by more than 50 percent due to ACRT. Additionally, we will discuss the effect of forced melt convection on the axial zinc and dopant segregation profile. Electrical characterization, spectrometric performance and purity analysis of the grown crystals will be presented.

In this contribution we show an improvement of a spectroscopic response of CZT X-ray detector operating at high fluxes of X-ray tube by simultaneous infrared light illumination with a wavelength of 1200 nm. CZT detectors usually suffer from a polarization effect while their internal electric field can be strongly deformed due to a trapping of photogenerated holes. We describe a mechanism of an optically induced depolarization peaking at photon energy of about 1 eV (~1240 nm) due to an optical transition of electrons from the valence band to the deep level. The depolarization effect is accompanied by a decrease of the detector current which results in a lower noise entering the preamplifier of detector readout circuit. We have observed that it is possible to restore originally distorted X-ray spectra using additional 1200 nm LED illumination with a photon flux of ~10^16 cm^-2s^-1 at approximately two times higher X-ray flux than without LED. The number of detected counts was in the range of 10^5-10^6mm^2s^-1. The restoration of the spectrum by continuous infrared light is accompanied by decrease of dark current. We explain this effect by light induced changes of profile of the electric filed that leads to decrease of the electron current injected from the cathode.

We have developed the current integration mode CdTe imaging device with 100fps movie mode. The pixel pitch is 100um, and detector size is about 50mm x 45 mm with 4-CdTe-ASIC units and 1mm thick-CdTe. The data correction algorithms were developed and installed in FPGA and MPU with real time collection. We can find clear image with high contrast as direct conversion, for example, pipe-edge thickness detection, penetration image and movie of mechanical watch and so on. We can observe detail connection in printed circuit board by using rotation movie mode. Also it has high sensitivity in high energy region, so we can apply to get real-time movie in operation. We will show the demonstration movie and detail of this detector.

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.

In this work, two Hg-based chalcogenides were investigated in detail to reveal their potential capability of radiation detection at room temperature (RT). Cs2Hg6S7, with a bandgap of 1.63 eV, which is designed by the dimensional reduction theory proposed by our group, were prepared and characterized. α-HgS, with a bandgap of ~2.10 eV, as a precursor used for the ternary compound synthesis, was also proposed and further investigated. For Cs2Hg6S7, the crystals tended to crystallize into needle form with small grains. Here, the conditions of Bridgman melt growth were optimized to obtain relatively large single crystals. The slight excess of Cs2S as a fluxing agent during growth was found to facilitate better crystallization and large grains. Interestingly, no inclusion or secondary phase was found in the as-grown single crystals. The improvement of bulk resistivity from ~10^6 Ωcm to 10^8 Ωcm was also achieved through the control of stoichiometry during crystal growth. For α-HgS crystals, both physical vapor transport and chemical vapor transport methods have been applied. By modifying the transport temperature and transport agent, single crystal with size about 3x1.5 mm^2 was grown with resistivity higher than 10^11 Ωcm. Photoluminescence (PL) revealed that multiple peaks observed in the 1.6-2.3 eV range and excitonic peak from for α-HgS single crystals were observed indicating good crystalline quality. Finally, the planar detectors for both crystals were tested under Co57 gamma ray source. Both of the crystals showed reasonable gamma ray response, while α-HgS crystals could respond at a relatively higher counting rate.

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.

Thallium activated sodium iodide (NaI:Tl) is one of the most widely used gamma-ray scintillators. Commercially available NaI:Tl scintillators are typically characterized by a gamma-ray energy resolution of 6.5% at 662 keV and a scintillation decay time constant of 230 ns. Energy resolution, non-proportionality and scintillation decay time are improved when the crystal is co-doped with alkaline earth metals. The energy resolution of NaI:Tl+ is improved to 5.3% and the decay time is simultaneously reduced to 170 ns with Sr or Ca co-doping. The improvement in energy resolution, non-proportionality and decay time is likely due to the suppression of slow scintillation processes in NaI:Tl. We also demonstrated that Li+ can be substantially incorporated into the matrix of NaI under an optimized crystal growth process. The incorporation of Li+ introduces efficient neutron detection capability into an already successful gamma scintillator. Single crystals of Li co-doped NaI show similar gamma performance as standard NaI:Tl. Exceptional gamma-neutron pulse shape discrimination (PSD) has been demonstrated in all Li co-doped NaI crystals with up to 8% Li concentration. PSD Figure-of-Merits are up to 4.4 depending on Li content.

Gamma rays produced passively by cosmic ray interactions and by the decay of radioelements convey information about the elemental makeup of planetary surfaces and atmospheres. Orbital missions mapped the composition of the Moon, Mars, Mercury, Vesta, and now Ceres. Active neutron interrogation will enable and/or enhance in situ measurements (rovers, landers, and sondes). Elemental measurements support planetary science objectives as well as resource utilization and planetary defense initiatives. Strontium iodide, an ultra-bright scintillator with low nonproportionality, offers significantly better energy resolution than most previously flown scintillators, enabling improved accuracy for identification and quantification of key elements. Lanthanum bromide achieves similar resolution; however, radiolanthanum emissions obscure planetary gamma rays from radioelements K, Th, and U. The response of silicon-based optical sensors optimally overlaps the emission spectrum of strontium iodide, enabling the development of compact, low-power sensors required for space applications, including burgeoning microsatellite programs. While crystals of the size needed for planetary measurements (>100 cm3) are on the way, pulse-shape corrections to account for variations in absorption/re-emission of light are needed to achieve maximum resolution. Additional challenges for implementation of large-volume detectors include optimization of light collection using silicon-based sensors and assessment of radiation damage effects and energetic-particle induced backgrounds. Using laboratory experiments, archived planetary data, and modeling, we evaluate the performance of strontium iodide for future missions to small bodies (asteroids and comets) and surfaces of the Moon and Venus. We report progress on instrument design and preliminary assessment of radiation damage effects in comparison to technology with flight heritage.

The detection of neutrons in the presence of gamma-ray fields has important applications in the fields of nuclear physics, homeland security, and medical imaging. Organic scintillators provide several attractive qualities as neutron detection materials including low cost, fast response times, ease of scaling, and the ability to implement pulse shape discrimination (PSD) to discriminate between neutrons and gamma-rays. This talk will focus on amorphous organic scintillators both in plastic form and small-molecule organic glass form. The first section of this talk will describe recent advances and improvements in the performance of PSD-capable plastic scintillators. The primary advances described in regard to modification of the polymer matrix, evaluation of new scintillating dyes, improved fabrication conditions, and implementation of additives which impart superior performance and mechanical properties to PSD-capable plastics as compared to commercially-available plastics and performance comparable to PSD-capable liquids. The second section of this talk will focus on a class of small-molecule organic scintillators based on modified indoles and oligophenylenes which form amorphous glasses as PSD-capable neutron scintillation materials. Though indoles and oligophenylenes have been known for many decades, their PSD properties have not been investigated and their scintillation properties only scantily investigated. Well-developed synthetic methodologies have permitted the synthesis of a library of structural analogs of these compounds as well as the investigation of their scintillation properties. The emission wavelengths of many indoles are in the sensitive region of common photomultiplier tubes, making them appropriate to be used as scintillators in either pure or doped form. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This work has been supported by the U.S. Department of Energy Office of Nonproliferation Research and Development (NA-22) and by the Defense Threat Reduction Agency (DTRA).

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.

Our prior investigations showed that alloying CdTe with selenium results in improved material characteristics, such as a reduction in the concentration of secondary-phase particles, better compositional uniformity and less sub-grain boundary networks, as compared to CdTe/CdZnTe. However, by alloying with Se, the band-gap of CdTeSe is significantly reduced from the value for CdTe, which is the main drawback for high-resistivity CdTeSe compounds useful for radiation detection. In order to increase the band-gap, we are now growing Cd1-xZnxSeyTe1-y crystals for detector applications. The effect of Se alloying with CdZnTe will be discussed in terms of the concentration of secondary phases, stress-related defects such as sub-grain boundaries and their networks. Characterization results for the transport properties of the as-grown materials will also be discussed.

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.

Aluminum (Al) doped ZnO with very high Al concentration acts as metal regarding its electrical conductivity. ZnO offers many advantages over the commonly-known metals being used today as electrode materials for nuclear detector fabrication. Often, the common metals show poor adhesion to CdZnTe or CdTe surfaces and have a tendency to peel off. In addition, there is a large mismatch of the coefficients of thermal expansion (CTE) between the metals and underlying CdZnTe, which is one of the reasons for mechanical degradation of the contact. In contrast ZnO has a close match of the CTE with CdZnTe and possesses 8-20 times higher hardness than the commonly-used metals. In this presentation, we will explore and discuss the properties of CdZnTe detectors with ZnO:Al contacts.

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.

Plastic scintillators are widely deployed for ionizing radiation detection, as they can be fabricated in large sizes, for high detection efficiency. However commercial plastics are limited in use for gamma spectroscopy, since their photopeak is too weak, due to low Z, and they are also limited in use for neutron detection, since proton recoils are indistinguishable from other ionizing radiation absorption events in standard plastics. We are working on scale up and production of transparent plastic scintillators based on polystyrene (PS) with high loading of bismuth metallorganics for gamma spectroscopy, and with lithium metallorganics for neutron detection. When activated with standard organic fluors, PS scintillators containing 8 wt% bismuth provide energy resolution of 11% at 662 keV. A PS plastic formulation including 1.3 wt% lithium-6 provides a neutron capture peak at 525 keVee, with 11% resolution for the capture peak and 90% efficiency for thermal neutron capture in 2mm thickness. Acknowledgements This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and has been supported by the US DOE National Nuclear Security Administration, Defense Nuclear Nonproliferation Research and Development under Contract No. DE-AC03-76SF00098

There is significant interest in developing efficient, direct conversion, neutron sensitive solid-state radiation detector materials with the ability to discriminate between photon and neutron events. Recently, this has led several research groups to pursue uranium dioxide (UO2) single crystals as a detection material due to the large reaction energy (~185 MeV) from a neutron induced fission event. The resulting electrical pulse, generated primarily by the energetic fission fragments, is expected to be on the order of 165 MeV, which is much greater than current detection schemes which rely on reaction energies between 2-6 MeV. The primary technical challenge to the successful fabrication of UO2 devices is the lack of high quality (semiconductor grade) single crystals of UO2. The high melting point of UO2 (~2878°C) precludes the use of traditional melt growth techniques like Czochralski. While exotic melt growth techniques such as arc fusion, cold crucible, and solar furnace have successfully grown UO2, the crystal quality suffers from both thermal strain and oxygen non-stoichiometry, two particularly difficult challenges inherent to uranium oxide materials. Crystal growth of UO2 by the hydrothermal synthesis technique has never been investigated, although the method has been successfully applied to the synthesis of other refractory oxides. In this talk, we will present growth of UO2 single crystals from a variety of hydrothermal solutions at temperatures below 650C. X-ray diffraction confirmed the stoichiometric nature of the samples and X-ray photoelectron spectroscopy determined the photoelectric work function of two crystal orientations. Preliminary proof-of-concept irradiation studies of a simple UO2 resistive detector will also be presented.

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.

The abstract is not available

During the transition period between closure of Beamline X27B at BNL’s NSLS and the opening of Beamline MID at NSLS-II, we began operation of LBNL’s ALS Beamline 3.3.2 to carry out our radiation detection materials RD. Measurements performed at this Beamline include, X-ray Detector Response Mapping and White Beam X-ray Diffraction Topography (WBXDT), among others. We will introduce the capabilities of the Beamline and present the most recent results obtained on CdZnTe and scintillators. The goal of the studies on CdZnTe is to understand the origin and effects of subgrain boundaries and help to visualize the presence of a higher concentration of impurities, which might be responsible for the deterioration of the energy resolution and response uniformity in the vicinity of the sub-grain boundaries. The results obtained in the second year of measurements will be presented.

Crystal detectors have been used widely in high energy and nuclear physics experiments, medical instruments and homeland security applications. A crucial issue for crystal detectors to be used for future HEP experiments at the energy and intensity frontiers is radiation damage by ionization dose as well as charged and neutral hadrons. This paper reports recent investigations on radiation damage in various crystal scintillators. Irradiations up to 340 Mrad of ionization dose, 1E16 p/cm^2 fluence and 1016 n/cm2 fluence were carried out at the JPL total ionization dose facility and the Los Alamos Neutron Science Center, respectively. Results of these investigations show excellent radiation hardness of bright and fast LYSO crystals which may provide a stable detector in an extreme harsh radiation environment, such as the proposed HL-LHC.

The traditional method for electron lifetime measurements of CdZnTe (CZT) detectors relies on using the Hecht equation. The procedure involves measuring the dependence of the detector response on the applied bias and applying the Hecht equation to evaluate the mu-tau product, which in turn can be converted into the carrier lifetime if the mobility is known. Despite general acceptance of this technique, which is very convenient for comparative testing of different CZT materials, the assumption of a constant electric field inside a detector is unjustified. In the Hecht equation, this assumption means that the drift time would be a linear function of the drift distance. This condition is rarely fulfilled in practice at low applied biases where the Hecht equation is most sensitive to the mu-tau product. As a result, researchers usually take measurements at relatively high biases, which work well in the case of the low mu-tau material, <10-3 cm2/V, but give significantly underestimated values for the case of high mu-tau crystals. In this work, we applied the time-of-flight (TOF) technique to measure the electron lifetimes in long-drift-length (3 cm) standard-grade CZT detectors produced by Redlen Technologies. The TOF-based techniques are traditionally used for monitoring the electronegative impurity concentrations in noble gas detectors by measuring the electron lifetimes. We found the electron mu-tau product of tested crystals is in the range 0.1-0.2 cm2/V, which is an order of the magnitude higher than any value previously reported for CZT material. In this work, we reported the measurement procedure and the results. We will also discuss the applicability criteria of the Hecht equation for measuring the electron lifetime in high mu-tau product CZT.

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.

In this work, we reconfigured the design of the electrodes, incorporating the high-granularity position-sensitive 3D concept into a larger geometrical form factor, e.g., hemispheric detectors, to improve the uniformity of charge collection and the energy resolution. We designed and fabricated new position-sensitive hemispheric detectors and measured the pulse-height spectra and acquired charge transport data and other electrical measurements with different sealed radioactive sources before and after modifying the design, and compared their performance to identify the optimum configuration. We then applied charge-loss corrections by utilizing the x-y-z positional information from the charge-sensing pads for each event. Based on our simulations and experimental data, we optimized a new configuration for our position-sensitive hemispheric detectors that can effectively be fabricated as large as 20x20x15-mm3 size. Furthermore, our simulation suggests that we can achieve an energy resolution of <1% (FWHM) at 662 keV from even 10x10x5 mm3 sized position-sensitive hemispheric detectors using average-grade CZT crystals.

Point defects and their concentrations play an important role in limiting the electrical and spectral properties of crystals. It is observed that the crystal-growth process causes the generation of different types of point defects, and these defects create non-uniformities that can be detrimental to device performance. In this research Cd1-xZnxTe1-ySey (CZTS) crystals grown by Bridgman and Travelling heater methods are studied for their point defects. The focus is on the types of defects, their concentrations and the variations with the selected growth method. In addition the effects of growth-related medium and deep energy traps and their corresponding densities are related to the resistivity, life-time of charge carriers and -product for electrons.

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.

In our prior research we investigated room-temperature radiation detectors (CZT, CMT, CdMgTe, CTS, among other compound semiconductors) for point defects related to different dopants and impurities. In this talk we will report on our most recent research on newly grown CZT crystals doped with In, In+Al, In+Ni, and In+Sn. The main focus will be on the study of dopant-induced point defects using deep-level current transient spectroscopy (i-DLTS). In addition the performance,  product, gamma-ray spectral response and internal electric field of the detectors were measured and correlated with the dopant-induced point defects and their concentrations. Characterization of the detectors was carried out using i-DLTS for the point defects, Pockels effect for the internal electric-field distribution, and -ray spectroscopy for the spectral properties.

CsPbBr3 has direct band gap (orange color, 2.25 eV), high density (4.85 g/cm3), attenuation coefficient comparable to CZT, and high resistivity ~10^9 ohm∙cm. These fundamental physical properties of CsPbBr3well meet the requirements for gamma-ray detector materials. CsPbBr3 exhibits the carrier mobility-lifetime product in the order of 10^-4 cm2/V promising enough to be further developed for practical applications. The major challenge in the process to further enhance the detection performance is the carrier traps present at a deep level of the energy gap which should be minimized. We report the synthesis, purification, crystal growth and physical characterization of the CsPbBr3 crystals obtained by new processes we developed for highly pure materials with reduced carrier traps. The starting binary materials were prepared by reaction of Cs2CO3/HBr and Pb(ac)2/HBr in aqueous solution. Purification of materials was performed by sublimation, bromination with HBr gas, and filtration of molten materials. Large single crystals were grown by the vertical Bridgman and EelectroDynamic Gradient method and cut to the dimensions appropriate for assessment of the material for gamma-ray detector applications. All characterization including optical characteristics, charge transport properties, photoconductivity, and gamma-ray spectroscopy from the new single crystals of CsPbBr3 will be presented. In addition, the charge carrier traps profile has been studied for this compound by Deep-Level Transient Spectroscopy (DLTS), Thermally Stimulated Luminescence (TSL), and Photoluminescence (PL) and will be presented.

Thallium based chalcogenide and halide semiconductors such as Tl4HgI6, TlGaSe2, Tl6SeI4 and Tl6SI4 are promising materials for room-temperature hard radiation detection. They feature appropriate band gaps, high mass densities and facile growth technology. However, these materials are being plagued by the Tl oxides impurity from Tl precursor or Tl containing binary precursors, which leads to problems including tube breakage, parasitic nucleation and detector performance deterioration. In this work, we present a facile way to chemically reduce Tl oxidations, and then eliminate oxygen impurity by adding high-purity graphite powder during synthesis and crystal growth. We also further investigated the reactivity between Tl oxides and graphite. The detector performance of Tl6SeI4 crystal was dramatically improved after lowering/removing the oxygen impurities. This result not only indicates the significance of removing oxygen impurity for improving detector performance. Our results suggest that the chemical reduction method we developed by adding carbon powder during synthesis is highly effective in substantially reducing oxygen impurities from Tl containing materials.

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.