This PDF file contains the front matter associated with SPIE Proceedings Volume 10762, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Scintillators are important materials for radiation detection applications such as homeland security, geological exploration, and medical imaging. Scintillators for nuclear nonproliferation applications in particular must have excellent energy resolution in order to distinguish the gamma-ray signatures of potentially dangerous radioactive sources, such as highly enriched uranium or plutonium, from non-threat radioactive sources such as radioactive tracers used in medical imaging. There is an established need for scintillators with energy resolution in the 1-2% range at 662 keV. However, there are challenges surrounding the development of this new generation of high light yield/high resolution scintillators; for example, the high cost of production due to low crystal yield and slow growth process, and crystal inhomogeneity. We will discuss efforts focused on developing recently discovered high performance scintillators K(Sr,Ba)2I5:Eu, Cs4(Ca,Sr)I6:Eu and Cs2Hf(Cl,Br)6 that have potential for meeting nuclear security needs. Growth parameters for these materials have been optimized, allowing the growth of excellent quality single crystals measuring up to one-inch in diameter via the vertical Bridgman technique at translation rates between 1 and 5 mm/h. These scintillators materials have excellent properties with light yields between 30,000 and 120,000 ph/MeV, and energy resolutions between 2.3 and 4.6% at 662 keV.

Invited talk Performance optimization of large diameter SrI2(Eu) detector assemblies - Light extraction - Readout types - Integration time optimization - Digital signal processing and correction - Environmental performance

In high energy physics (HEP) and nuclear physics experiments, total absorption electromagnetic calorimeters (ECAL) made of inorganic crystals are known for their superb energy resolution and detection efficiency for photon and electron measurements. A crystal ECAL is thus the choice for those experiments where precision measurements of photons and electrons are crucial for their physics missions. Because of its ultrafast scintillation component with sub nanosecond decay time, BaF2 crystals are considered as a candidate for an ultrafast crystal calorimeter for future high energy physics experiments, where unprecedented event rate and radiation environment are expected. Undoped BaF2, however, has also a slow scintillation component with 600 ns decay time, which causes pile-up. Rare earth doping with La, La/Ce and Y was found effective to suppress the slow component. While typical fast/slow (F/S) ratio observed in undoped BaF2 is 1/5, La doping and La/Ce co-doping were found to improve this ratio to about 1/1, which is considered not sufficient for pile-up suppression. It was found recently that yttrium doping is more effective in improving the F/S ratio, while maintaining the intensity of its ultrafast light not changed. This novel ultrafast scintillator with excellent radiation hardness will find wide applications for future HEP experiments, ranged from ultrafast timing detector at the HL-LHC to ultrafast calorimeter for the proposed Mu2e-II experiment at Fermilab. Applications of this ultrafast crystal scintillator for Gigahertz hard X-ray imaging for the proposed Marie project at LANL will also be discussed.

The Smithsonian Astrophysical Observatory (SAO) in collaboration with Stanford Research Institute (SRI) has been developing monolithic CMOS detectors for use as astronomical soft X-ray imaging spectrometers since 2008. The long term goal of this collaboration is to produce X-ray Active Pixel Sensor (APS) detectors with Fano limited performance over the 0.1-10keV band for “Facility Class” missions such as Lynx. Since CMOS x-ray imagers consume very little power; are inherently ”radiation hard”; have high levels of integration, and are capable of very high read rates they are ideal for “Small Satellite” missions as well. SAO/SRI CMOS imagers are presently being proposed for several, more immediate X-ray “Small Sat” real and concept missions. CMOS device fabrication provides the most rapid path forward towards advances in virtually all types of integrated circuits. The same techniques and infrastructure that has produced tremendous capabilities in microprocessors, RAM and FPGAs are now being applied to CMOS based imaging detectors CMOS imaging detectors have found their way into high end consumer cameras and in various (non X-ray) astronomical missions, e.g. the flight imaging detectors for the SoloHi mission, the WISPR imager on the Parker Solar Probe. SAO is presently investigating three different devices that each embody technology that would be highly desirable in an x-ray imaging spectrometer; these are: back thinned high sensitivity NMOS PPD devices; NMOS devices with stitchable reticles; and monolithic PMOS devices that collect photo-holes instead of photo electrons. The back-thinned, high sensitivity NMOS PPD devices, known as Big Minimal IIIs (BMIII) were specifically funded and designed for soft x-ray single photon counting. They embody a 1k by 1k array of 6 Transistor (6T) 16µm PPD pixels. Each pixel has a 135 μV/e sense node. The stitchable reticle devices, known as “Mk by Nk”, can be made seamlessly in any format which fits on a silicon wafer. They consist of an array of 6 Transistor (6T) 10μm PPD pixels (for these test devices M=N=1) with a sense node of 90 μV/e. A stichable reticle CMOS with a choice of format size would be ideal for large focal plane or for a narrow rectangular grating readout. The third device category is a small 256 by 256 16μm pixel PMOS device which collects holes instead of electrons with a 60μV/h+ sense node. SAO/SRI conventional NMOS CMOS devices known as the Big Minimal III (BigMinIII) have recently demonstrated the ability to detect and resolve X-rays with energies below 200eV. Even with this very good sub-1keV response, an NMOS astronomical instrument would still be fundamentally limited by charge collection, read and Random Telegraph Signal (RTS) noise particularly for soft, faint, extended sources and surveys. We have just for the first time performed very preliminary X-ray tests with monolithic FI PMOS devices. We present details of our new camera design and preliminary device performance with particular emphasis on those aspects of interest to single photon counting X-ray astronomy.

A digital deconvolution method with pile-up reconstruction has been proposed for scintillator detectors for high rate photon-counting X-ray imaging applications. The detector signal was modeled as an exponential decay waveform convoluted with the single photon response of the SiPM detector. An impulse signal can be obtained by digital deconvolution (unfolding) with much shorter duration, which was then used for energy estimation followed by a trapezoid filter and pile-up discrimination. The whole digital deconvolution algorithm has been synthesized and verified by both SIMULINK simulation and experimental tests. The prototype of the detector and the readout electronics were developed for demonstration, using 3 mm x 3 mm x 10 mm LYSO scintillator coupled with a 3 mm x 3 mm SenSL SiPM. A 14 bit, 100 MSPS ADC was used to sample the analog waveform and the digital filter was implemented in a Xilinx Kintex 7 FPGA. The signal width was shortened from ~250 ns to 10~20 ns and then was shaped into trapezoidal pulse with 100 ns width. The energy was estimated from the trapezoid top for better signal collection and noise rejection. The unfolded pulses were used for pile-up discrimination and to reconstruct two pile-up signals from the overlapped trapezoid outputs. The energy performance of the prototype system was firstly validated by measuring the energy spectrums of ²⁴¹Am, ⁵⁷Co, ²²Na and ¹³⁷Cs radiation sources. The energy resolutions were measured to be 36.9%, 29.9%, 13.9% and 12.9% respectively at 59.5 keV, 122 keV, 511 keV and 662 keV in FWHM. High rate performance was evaluated by an X-ray generator. The maximum output counting rate was measured to 5.36 Mcps without saturation, comparing with the saturated counting rate of 2.34 Mcps using the original LYSO signals. The saturation counting rate using digital deconvolution was estimated to be up to ~7 Mcps fitted with the paralyzable dead time model, corresponding to ~20 Mcps input count rate.

Plastic scintillators incorporating 8 weight percent elemental Bismuth offer enhanced sensitivity and distinct photopeak spectra in the <1000 keV range typically used in radiation portal monitors. The Bismuth-loaded plastic is based on polyvinyl toluene with standard singlet fluors. It produces ~6,000 photons/MeV with a maximum emission at 430 nm and a ~10 ns decay. Energy resolution of 49% at 59.5 keV and 16% at 662 keV are obtained for a 14 in³ Bismuth plastic scintillator plate. Count rates compared to standard plastic scintillator of the same size reveal a sensitivity improvement of >5x in the <200 keV range. Future spectroscopic radiation portal monitors based on the Bismuth plastic scintillator could provide moderate resolution spectroscopy for radioisotope identification. In addition, the Bismuth plastic offers outstanding environmental stability to weathering effects, in contrast with standard plastic scintillator formulations.

Spectroscopic detection of gamma and neutron particles has widespread applications for research, defense and medical purposes. The dominant materials for the detection have been inorganic semiconductors, scintillation crystals, and plastics that are either prohibitively expensive or cannot produce characteristic photopeak. We report the synthesis of transparent nanocomposite monoliths comprising high-z nanoparticles for gamma photoelectric generation and conjugated organic matrix for visible photon generation. The energy transfer from the nanoparticles to lower-band-gap organic dyes was studied in connection with light yield. Synthesis of transparent monoliths capable of producing 662 keV gamma photopeak and discriminating gamma/neutron pulses will be described.

Polyvinyl Toluene (PVT) based plastic scintillators with varying dimensions and fluors have been characterized in terms of relative light output and spatial resolution. Scintillators were exposed to fast neutrons (~2 MeV), and images were obtained with a setup consisting of an EMCCD camera, a mirror and a light-tight apparatus. Among scintillators with 2.0% Flrpic and 10.16 cm (4 inch) diameter, the 10.5-mm thick scintillator featured the highest light output while 3.0- mm provided the best spatial resolution. The deuterated 3.0-mm thick scintillator doped with 2.0% Flrpic showed a worse performance in terms of both light output and spatial resolution compared to that of undeuterated scintillator with the same thickness but doped with 2.0% X-Flrpic. This study reveals the effects of presence of deuterium in PVT, the thickness of scintillator, and the fluor on the light output and spatial resolution of plastic scintillator.

Pulse shape discrimination in plastic scintillators has been of much interest in recent years. As with many innovative technologies, initial formulations for PSD plastics provided new capabilities that required much in-depth research to fully develop and refine. Herein we describe results from extensive optimization studies which have led to the development of PSD plastics with markedly improved scintillation performance and physical properties. Results of exploring different plastic matrices as well as a variety of secondary dyes are reported and optimum components are described. Due to the large concentration of additives required to manifest optimal PSD properties in plastic scintillators, the physical stability can be limited and the mechanical properties of PSD plastics are inferior to standard engineering plastics. Practical and theoretical solutions have been developed to address the physical stability and mechanical deformation problems in PSD plastics, and this work has resulted in physically stable scintillators with robust mechanical properties. Performance deterioration on increasing the size of PSD plastics is also addressed. At large sizes, physical and performance characteristics are much more sensitive to preparation conditions and compositional alterations as compared with small scintillators, and efforts to improve these properties are described. Finally, efforts to incorporate aromatic lithium compounds into PSD plastics are summarized and the effects of the lithium compounds on scintillation, stability, and attenuation are discussed.

The technological advances introduced by additive manufacturing techniques have significantly improved the ability to generate functional composites with a wide variety of mechanical and optical properties. Progress in the additive manufacturing of scintillating particle composites could enable new capabilities that span applications in nuclear nonproliferation, nuclear energy and basic science. The present work focuses on developing capabilities for additively manufacturing scintillating particle composites where successful implementation could enable cost-effective highperformance detectors for a wide range of applications. The results demonstrate the optical and response characteristics of arranged scintillating glass particle composites that are optically transparent, mechanically robust and respond to incident fast neutrons.

Scintillating dyes in polymer blends is a common tool used in radiation detection and its modifiability is a desirable attribute for different applications. Through nanocomposite loading, nanocrystals are generally employed to enhance scintillation either through radiative or non-radiative energy transfer. In this work similar methods are pursued with focus in the UV region through UV emitting nanocluster such as ZnO and CdS. A wide range of UV emission nanocrystals are selected and combined with different polymer and dyes demonstrating both quenching and enhancement. Preliminary results show not only dependency of the wavelength but also the polymer medium indicating different energy transfer paths. Compared to samples without nanocrystal the light yield was increased throughout different combinations.

Linear avalanche photodiodes are ultra high sensitive optical detectors for low luminescent applicants. Low noise silicon reach-through avalanche photodiodes are designed and implemented through 0.35 μm high voltage CMOS process. Separated absorption multiplication (SAM) structure with vertical n++/pi/p+/pi/p five layers is adopted. The remarkable low noise is archived while maintaining linear multiplication. The photo sensitive area is 200 μm in diameter. The typical reach-through voltage and the breakdown voltage is tested to be 55 V, and 176 V, respectively. The dark current at the gain M=100 is tested to be 10 - 100 pA. The responsive wavelength is 400-1000 nm. The peak responsivity is tested to be 25 A/W at 850 nm wavelength to show the successful near infrared enhanced responsivity. The excess noise factor is estimated to be 4, much lower than those in the reported high voltage CMOS avalanche photodiodes, but close to the commercial APD fabricated through special process.

Measurement results of charged particles (atmospheric muon) detection efficiency of a scintillation detector based on polyvinyltoluene, manufactured for the anticoincidence system of the "Signal" device as part of the scientific apparatus for the spacecraft "Interhelioprobe", are presented. The efficiency measurement technique is based on determination of the ratio of triple and double coincidence of the signals arising as atmospheric mu-mesons pass through the system of detectors. The results of light collection simulation in scintillation detectors by the use of Monte Carlo method are presented.

Solar neutron observations are very important for understanding of nucleon acceleration mechanism in solar flares, but there are only a few tens of detection since the discovery in 1980. This is because most o solar neutron observations have been done from not space but the ground with insufficient sensitivity. We have designed very compact and high sensitive solar neutron and gamma-ray spectrometer utilizing a novel photo-sensor Silicon photo-multiplier (Si PM). This paper describes concept, design and performance of our detector for micro/nanosatellite applications.

Arrays of position-sensitive virtual Frisch-grid CdZnTe (CZT) detectors offer an economical approach to make high-efficiency and high energy-resolution gamma cameras for spectroscopy and imaging of radioactive sources. There are many application areas for such instruments including gamma-ray astronomy, medical and industrial imaging, environmental cleanup, nonproliferation and nuclear safeguards. Here, we present the design and results from testing of a 4x4 array mounted on a fanout substrate coupled to a front-end ASIC. The current array houses up to 16 detectors with a cross section of 6x6 mm3 and thickness of 2 cm. However, the array’s design provides flexibility to extend its dimensions in conjunction with the opportunity to replace faulty individual detectors or higher-performing detectors with thicknesses potentially increased up to 4 cm. Each detector is encapsulated inside an ultra-thin polyester shell and furnished with 5 mm-wide charge-sensing pads placed near the anode. For each gamma-ray event the signals on the pads are converted into X-Y coordinates and combined with the cathode signals (for the Z coordinates) to give 3D positional information of all interaction points, which provides a high-spatial-resolution imaging capability for the array. Moreover, the positional information can be used to correct for the detectors’ response non-uniformities due to the presence of crystalline defects, which, in turn, allows the developers to use relatively economical standard-grade (unselected) CZT crystals, while retaining the high spectroscopic performance comparable to the large-volume pixelated detectors produced from more expensive monolithic CZT crystals.

Recent progress with Cadmium Zinc Telluride (CZT) radiation sensors grown by the traveling heater method (THM) at Kromek is reported. Large volume monolithic pixelated detectors, 40×40×15 mm³ have been fabricated with good initial gamma spectroscopy response (< 2.5% energy resolution at 662 keV at room temperature without correction). After depth of interaction (DOI) correction, detector performance with < 1% energy resolution at 662 keV at room temperature has been obtained on pixelated 22×22×15 mm³ CZT detector. For medical imaging applications, 20×20×6 mm³ pixelated detectors exhibits < 3% energy resolution at 122 keV without correction. These results have been achieved via our proprietary THM crystal growth in combination with our robust device fabrication technique. Examples of progress in other areas of CZT development for gamma spectroscopy and imaging applications such as 40×40×5 mm³ cross-strip device for PET and Kromek’s general-purpose SPECT camera will also be presented.

Enormous effort has been exerted on research and development of CdZnTe (CZT) over the past two decades, as well as the pursuit of an alternative material to mitigate the disadvantages in today’s CZT material or provide comparable device performance at a lower cost of production. Although the quality of CdZnTe crystals has been improved drastically over the past few years and the material cost has steadily decreased, the yield of large-volume high-quality detector-grade CZT continues to be an issue due to its poor thermo-physical properties. TlBr was found to be a promising material to compete with CZT, but the contact degradation and device stability are still big issues and severely hinder the deployment of commercial TlBr-based devices for nonproliferation and national security applications. At BNL, we are developing a new compound Cd1-xZnx Te1-y Sey (CZTS) that holds promise as a potentially viable crystal for the replacement of CZT for some radiation detection and imaging applications. The addition of Se in the CZT compound has been found to be very effective in a drastic reduction of the sub-grain boundary network, leading to better compositional and charge-transport homogeneity. The new material has tremendous potential to increase the yield of high-quality detectors at a much lower cost of production. The reduction of the sub-grain boundary network can result in detectors with a lower voltage operation and increased detector thickness. Our efforts to develop CZTS for X- and gamma-ray radiation detector applications will be discussed in detail.

Cadmium Zinc Telluride (CD_1-xZn_xTe has become a crucial material for x-ray and gamma ray detection due to its wide band-gap, high atomic number and high density, which offer high efficiency and sharp spectroscopic resolution at room temperature. In addition, due to being lattice matched, it can also be used as substrate for the epitaxial growth of HgCdTe that can be used for infrared detection with high resolution. Hence, increasing the single crystal yield of CdZnTe from the grown ingot gained importance for the development of such detectors. In this study, a combination of modeling and experimental approaches has been developed in order to obtain high quality CdZnTe bulk crystals with good single crystal yield. A multi-zone Vertical Gradient Freeze (VGF) furnace was used for CdZnTe growth experiments. A global temperature model of the multi-zone furnace including complete geometry was employed using CrysMAS crystal growth modeling software. The correlation studies between the model and experimental behavior of the furnace are discussed in order to create a reliable model for temperature predictions. Temperature models were also included solid-liquid interface study in order to observe the interface shape at various stages of growth which would provide valuable insight about the quality and the yield of the ingot. Growth parameters and crucible geometries were estimated by CrysMAS simulations and interchanged between experiments. Effectiveness of temperature models and simulations was supported by experimental results such as single-crystalline yield, grain evolution and crystalline quality comparison by DCRC measurements of five successful crystal growths with moderate single crystal grain sizes.

The High Resolution Energetic X-ray Imager (HREXI ) is a coded-aperture imaging telescope that utilizes a large closely-tiled array of CdZnTe (CZT) detectors, each 19.9 x 19.9 x 3mm with a 32 x 32 pixel (604μm) for coded aperture X-ray imaging (3 - 200 keV) of cosmic X-ray sources and transients. Each CZT crystal is read out by an ASIC incorporating, for the first time, Through Silicon Vias (TSVs). These TSVs replace the wire bonds for this ASIC, originally designed for the Nuclear Spectroscopic Telescope Array (NuSTAR) focusing hard X-ray telescope. The TSVs allow flip-chip bonding of the ASIC to the PCB board electronics for processing of the data. The new TSV-ASICs will enable closer tiling and larger imaging arrays which require faster, more efficient ASIC testing and calibration at the die level. We have designed and developed an ASIC Test Stand (ATS) for rapid ASIC testing prior to bonding to CZT. We demonstrate how ASIC die-level testing with the ATS can be performed rapidly with rigidly spaced micro-pogo pins supported by an FPGA readout.

Electric field measurements based on cross-polarizers technique on crystals showing Pockels effect are nowadays relatively widely used for characterization of detector materials such CdTe, CdZnTe, CdZnTeSe and GaAs. Our present study is focused on nonstandard cases, in which the electrodes have a non-planar geometry, especially strip and single pixel contact with opposite planar electrode. Electric field is simulated using Poisson’s equation and the transmittance distribution of the system consisting of the biased sample (Pockels cell) placed between two orthogonal polarizers is calculated. We compare the simulations with measurements on CdZnTe samples and discuss the limits of the electric field evaluation.

Cadmium Zinc Telluride (CdZnTe) is a good candidate for detection of x-ray and gamma-rays due to its high atomic number and large bandgap. CdZnTe is a II-VI group semiconductor and by changing ZnTe concentration, its properties can be altered. CdZnTe crystals having 4% ZnTe is commonly used as a substrate for Mercury Cadmium Telluride (HgCdTe) which is an important absorbing material for infrared imaging applications. For x-ray and gamma-ray detection, on the other hand, ZnTe concentration is kept around 10%. Due to high resistivity of CdZnTe crystals, preparation of surfaces prior to deposition of electrodes is important. After cutting and mechanical polishing, subsurface damages are observed on the crystals, which have a negative effect on the resistivity of the crystal near to the surface alongside with the dangling bonds on the surface. Decrease in the resistivity results in high leakage current that hinders the collection of electrons produced by absorption of photons. In addition, to have a strong bonding with electrode metal, surface should be clean from contaminants like oxygen and carbon. Achieving clean surface with low leakage current can be achieved by employment of chemical polishing step prior to electrode deposition. Bromine-alcohol solutions are used for chemical polishing without much control over the etching conditions. In this study, we report on the results of optimization study of chemical polishing by bromine-alcohol. Different alcohols (methanol, ethanol, propanol) were employed with different concentrations and etching durations. In addition, etching is conducted for different orientations to examine orientation dependency of the solution.

CdZnTe (CZT) is proved to be a perfect material during the fabrication of detectors for X-ray and Gamma ray. However, Te inclusion is one of the main defects in CZT crystal which influences the electrical and spectroscopic properties of the detectors. This paper presents optimization of hot zone design and operating conditions by direct mixed solution growth (DMSG) method in order to reduce the formation of Te inclusion. The growth temperature is 890°C and the growth rate is 5mm/day. With the temperature gradient increased from 20K/cm to 40K/cm, the number of Te inclusion is reduced sharply while the size of Te inclusion is still large. When accelerated crucible rotation technique (ACRT) is introduced, the size of Te inclusion is reduced significantly. Large-size Te inclusion almost disappears under IR imaging. The density of Te inclusion which is larger than 1×10⁴cm³. The resistivity of the as grown crystal is higher than 10¹⁰Ωxcm. At last, the influence of ACRT sequences on Te formation is discussed.

Thallium bromide (TlBr) is a wide bandgap, compound semiconductor with high gamma-ray stopping power and promising physical properties. Large single crystalline defect-free Bridgman boules of 2-inches in diameter were grown for fabricating high Figure of Merit (defined under SIGMA program) radiation detectors for homeland security applications. However, the electro-migration of Br- ions towards anode and their reaction with the contact have long been known to adversely influence the lifetime of TlBr devices. We report on the performance of TlBr devices with Tl-contacts which minimizes the effects of polarization. Results indicate that vapor-deposited Tl-contacts are highly ohmic. Unlike devices with Pt and Au contacts, devices with Tl-contacts do not exhibit the short term (100s of hours) fluctuations in the spectroscopic response. A significant reduction of polarization even before device conditioning is clearly observed in detectors with Tl-contacts. Furthermore, these devices show a stable behavior and can work under much lower electric fields. Energy resolution in the range of 2-2.5% at 662keV was obtained using virtual Frisch-grid (10mm thick) and pixelated (5.5mm thick) TlBr devices with Tl-contacts without any digital correction. Large area 20mm x 20mm x 5.5mm pixelated detectors with 11×11 and 15×15 pixel patterns were also fabricated using Tl-contacts. The planar Tl-contact devices exhibited a stable gamma detection performance for up to 14-months under continuous bias (~1000 V/cm) and irradiation.

High purity, CVD grown diamond is a good candidate material for beta particle detection at elevated temperature in the presence of a gamma ray background. Due to its wide band gap, low noise detector operation is possible at temperatures in excess of 200 °C. Its low atomic number limits its gamma-ray interaction probability. Stacked diamond detectors operated in coincidence can further reduce background due to gamma-ray interactions. In addition, high charge carrier mobility and high breakdown voltage enable high count rate operation. In this paper we report on gamma-ray and beta particle detection of CVD diamond detectors with thickness ranging from ~ 0.1 mm to 0.5 mm. CVD grown diamond materials were acquired from Element Six. Planar devices were fabricated by depositing Au/Cr contacts by thermal evaporation. Measurements of single diamond detectors and stacked detectors operated in coincidence as well as measurements at elevated temperatures are presented in this paper.

In this paper, correlation between CMZT melt state and structure properties of crystals, grown by vertical Bridgman method, was investigated. The Cd_0.9-xMn_xZn_0.1Te crystals with various Mn composition (x = 0.1; 0.2) were grown by two-step preparation method from high purity elemental components. We have conducted series of crystal growth runs with different melt superheating degree over the alloys melting temperature. As a result, we have got the ingots with various crystalline structures and properties. It was concluded that worth crystalline structure had the bulks which were grown from the melt with lowest superheating degree. We have determined also that band gap rose (from 1.67 at x=0.1 to 1.79 eV at x=0.2) with Mn content increasing.

We discriminated various concentrations’ contrast mediums by spectral photon-counting CT imaging. Contrast media increase the contrast of tissues in x-ray computed tomography (CT) imaging. Conventional x-ray CT uses contrast agent liquids including high x-ray absorption materials like iodine. Spectral photon-counting computed tomography (SPCCT) imaging has the capability of discriminate each contrast mediums with low concentration in one scan by their K-edge if its energy is located in the detectable energy range. The purpose of our research is to reveal the discriminability of contrast mediums by K-edge imaging under the various conditions of concentration included in a water included acrylic phantom with low x-ray exposure.

We present the results of ongoing characterization of Cadmium Zinc Telluride (CZT) semiconductors produced by Redlen Technologies. In particular we hope to determine their viability for future X-ray astronomy missions such as the High Energy X-ray Probe (HEX-P). The fully fabricated hybrid detectors consist of CZT crystals with a collecting area of 2 cm × 2 cm and thickness of 3 mm mounted on a custom pixelated ASIC originally designed for the Nuclear Spectroscopic Telescope Array (NuSTAR) mission, which launched in 2012. We present the results of inter-pixel conductance and leakage current tests as well as spectral characterization using an ²⁴¹Am source. Although further calibration and testing is necessary to determine the capabilities of these detectors, preliminary results indicate that Redlen CZT will be able to achieve spectral resolution and noise levels comparable to those of the CZT detectors currently in use aboard NuSTAR.

Laser processing of high-resistivity p-CdTe semiconductor crystals and CdTe-metal interfaces has been used to obtain diode structures for X/γ-ray detectors. The relative simple techniques of laser doping and metallization of the CdTe surface have been studied. Deposition of In onto the CdTe crystals was performed using YAG:Nd laser pulses (1064 nm, 8 ns) in two ways: (a) laser transfer of a thin In film, pre-deposited on the glass substrate by laser ablation of an In target irradiated through the glass; (b) laser incorporation of In into the CdTe surface region by irradiation of an In target through the CdTe. Deposited In islands were revealed on the CdTe surface by SEM imaging. Photoconductivity spectra and I-V characteristics of the crystals before and after laser processing were measured. An increase in photosensitivity, particularly in the short wavelength region was observed for the metallized samples that was attributed to a decrease of the surface recombination velocity because of the built-in electric field due to the surface barrier formation. The structures demonstrated rectifying I-V characteristics. The resistivity of the metallized CdTe surface region exceeded that of the initial crystals in a few times therefore, the model of micro-p-n junctions, formed by simultaneous laser deposition of In and doping of local CdTe regions as result of penetration of In atoms (donors) into a thin CdTe surface layer, was considered. Micro-diodes, formed by laser-induced creation of n-type micro-regions, connected in the opposite direction, can be a reason of increased resistivity of the metalized CdTe surface.