This PDF file contains the front matter associated with SPIE Proceedings Volume 7449, including the Title Page, Copyright information, Table of Contents, the Conference Committee listing and introduction.

A special CdZnTe (CZT) device on THM grown crystal has been developed. The device has different work function metals on opposite electrodes yet operates at room temperature like a conventional back-to-back symmetric MSM detector and not a one directional Schottky diode device. Aiming at creating a big breakthrough in CZT imaging device technology, the special CZT device presented in this study is capable of increasing the photopeak count by up to 50% compared to conventional CZT imaging device while maintaining good room temperature energy resolution by not significantly trading off detector leakage current. Pixel pad size and interpixel gap on a 20x20x5 mm3, 8x8 pixel pattern that result in optimum detector efficiency and interpixel resistance are presented. Sensitivity improvement impact on other device configuration will also be discussed. The design is highly practical, reliable and suitable for mass production.

We report on the continued development and testing of unique types of Cadmium Zinc Telluride (CZT) detectors. Using large volume (10×20×20 mm³) CZT crystals, we contact various "dual anode" detector designs. We incorporate a segmented cathode with five regions so that the charge on all seven contacts can be used to determine the energy and the 3-D interaction location of detected X-ray and gamma-ray photons. We describe the status of the detector development program, emphasize strengths and weaknesses of the different contact configurations, and discuss possible applications of Dual Anode Detectors in radiation detection applications.

A CMOS application specific integrated circuit (ASIC) was developed for 3D Position Sensitive Detectors (PSD). The preamplifiers were optimized for pixellated Cadmium-Zinc-Telluride (CZT) Mercuric-Iodide (HgI2) and Thallium Bromide (TlBr) sensors. The ASIC responds to an ionizing event in the sensor by measuring both amplitude and timing in the pertinent anode and cathode channels. Each channel is sensitive to events and transients of positive or negative polarity and performs low-noise charge amplification, high-order shaping, peak and timing detection along with analog storage and multiplexing. Three methodologies are implemented to perform timing measurement in the cathode channel. Multiple sparse modes are available for the readout of channel data. The ASIC integrates 130 channels in an area of 12 x 9 mm² and dissipates ~330 mW. With a CZT detector connected and biased, an electronic resolution of ~200 e- rms for charges up to 100 fC was measured. Spectral data from the University of Michigan revealed a cumulative single-pixel resolution of ~0.55 % FWHM at 662 KeV.

A 4.7×4.7×9.5 mm³ Frisch collar device was fabricated from CdZnTe materials grown by the Traveling Heater Method (THM). The device was then characterized through probing with a highly collimated 662 keV gammaray source of ¹³⁷Cs. In a systematic series of experiments, the detector, at its best design, was probed using a collimated ¹³⁷Cs source. The results were confirmed through simulating the charge collection efficiency (CCE) maps of the device under the operated condition. It is proved that, unlike the planar configuration, the charge collection efficiency profile along the length of Frisch collar device is considerably improved. It is also shown that enhancement in spectral performance occurs due to the application of the Frisch collar to a planar device. This enhancement is due to the fact that the Frisch collar alters the nonuniform CCE profile in a planar device to a more uniform distribution in a Frisch collar device. Additionally, a technique to optimize this uniform distribution is investigated for a 5.0 × 4.7 × 19.6 mm³ Frisch collar device, while the experimental results are confirmed though numerical simulation. Based on this technique, there exists an optimum dielectric layer thickness for the CdZnTe Frisch collar device, for which the CCE profile has its best (most uniform) distribution and shows its best spectroscopic performance. The CdZnTe materials for this study were grown by THM at Redlen Technologies and the CdZnTe devices were fabricated and characterized at the S.M.A.R.T. Laboratory at Kansas State University.

We detail our new results from testing an array of 15-mm long virtual Frisch-grid CdZnTe detectors with a cathode signal readout-scheme intended to improve spectral response by correcting for electron trapping. We designed a novel electrode configuration for these long-drift detectors that ensures an energy resolution close to the statistical limit, and high detection efficiency. However, in reality, the quality of the crystals limits the performance of this type of device. Here, we describe the characterization of the array, show our preliminary results obtained with gamma-ray sources, and expound on their relation to our material-characterization data.

We report our simulations on the profile of the electric field in semi insulating CdTe and CdZnTe with Au contacts under radiation flux. The type of the space charge and electric field distribution in the Au/CdTe/Au structure is at high fluxes result of a combined influence of charge formed due to band bending at the electrodes and from photo generated carriers, which are trapped at deep levels. Simultaneous solution of drift-diffusion and Poisson equations is used for the calculation. We show, that he space charge originating from trapped photo-carriers starts to dominate at fluxes 10¹⁵-10¹⁶cm^-2s^-1, when the influence of contacts starts to be negligible.

Cadmium Zinc Telluride (CZT) is attracting increasing interest with its promise as a room-temperature nuclear-radiationdetector material. The distribution of the electric field in CZT detectors substantially affects their detection performance. At Brookhaven National Laboratory (BNL), we employed a synchrotron X-Ray mapping technique and a Pockels-effect measurement system to investigate this distribution in different detectors. Here, we report our latest experimental results with three detectors of different width/height ratios. A decrease in this ratio aggravates the non-uniform distribution of electric field, and focuses it on the central volume. Raising the bias voltage effectively can minimize such nonuniformity of the electric field distribution. The position of the maximum electric field is independent of the bias voltage; the difference between its maximum- and minimum-intensity of electric field increases with the applied bias voltage.

Some applications, particularly in homeland security, require detection of both neutron and gamma radiation. Typically, this is accomplished with a combination of two detectors registering neutrons and gammas separately. Recently, a new scintillator, Ce doped Cs₂LiLaCl₆ (CLLC) that can provide detection of both has been investigated for gamma and neutron detection. This material is capable of providing very high energy resolution, as good as 3.4% at 662 keV (FWHM), which is better than that of NaI(Tl). Since it contains ⁶Li, it can also detect thermal neutrons. In the energy spectra, the full energy thermal neutron peak appears near 3 GEE MeV. Thus very effective pulse height discrimination can be achieved with this material. The CLLC emission consists of two main components: Core-to-Valence Luminescence (CVL) spanning from 220 nm to 320 nm and Ce emission found in the range of 350 to 500 nm. The former emission is of particular interest since it appears only under gamma excitation. It is also very fast, decaying with a 2 ns time constant. This provides CLLC with different temporal responses under gamma and neutron excitation and it can be used for effective pulse shape discrimination.

We are working to perfect the growth of divalent Eu-doped strontium iodide single crystals and to optimize the design of SrI₂(Eu)-based gamma ray spectrometers. SrI₂(Eu) offers a light yield in excess of 100,000 photons/MeV and light yield proportionality surpassing that of Ce-doped lanthanum bromide. Thermal and x-ray diffraction analyses of SrI₂ and EuI₂ indicate an excellent match in melting and crystallographic parameters, and very modest thermal expansion anisotropy. We have demonstrated energy resolution with SrI₂(4-6%Eu) of 2.6% at 662 keV and 7.6% at 60 keV with small crystals, while the resolution degrades somewhat for larger sizes. Our experiments suggest that digital techniques may be useful in improving the energy resolution in large crystals impaired by light-trapping, in which scintillation light is re-absorbed and re-emitted in large and/or highly Eu²⁺ -doped crystals. The light yield proportionality of SrI₂(Eu) is found to be superior to that of other known scintillator materials, such as LaBr₃(Ce) and NaI(Tl).

A Rotational Modulator (RM) gamma ray imager, consisting of a single grid of lead slats rotating above an array of detectors with diameter equal to the slat spacing, has the capability of providing angular resolution significantly better than the geometric resolution (i.e., the ratio of detector diameter to mask/detector separation). The sensitivity, weight, and angular resolution are comparable to that of a coded aperture device, but with significantly less complexity. As the grid rotates, the transmission from a source is modulated on each detector between 0 and 100%. The count profile is cross-correlated with precalculated modulation profiles to produce an approximate source image. Deconvolution of this image with the known imager response can accurately resolve point sources and complex emissions. The appropriate deconvolution technique can achieve angular resolution better than the basic geometrical resolution of the instrument. A prototype RM developed at Louisiana State University features high sensitivity and energy resolution, functional angular resolution of 15, and a simple readout system. The detector array consists of 19 1.5 × 1 thick cerium-doped lanthanum bromide (LaBr₃:Ce) crystals. LaBr3 produces significantly more light than other common scintillators, offering < 3% FWHM energy resolution at 662 keV. A grid spaced ~1.2 m from the detection plane with slat width 1.5 offers a 13.8° field of view. We present our reconstruction technique, deconvolution algorithms, and simulated and experimental imaging results.

In this paper, we present the design and preliminary performance evaluation of a novel energy-resolved photon-counting (ERPC) detector for gamma ray imaging applications. The prototype ERPC detector has an active area of 4.4 cm x 4.4 cm, which is pixelated into 128 x 128 square pixels with a pitch size of 350 μm 350 μm. The current detector consists of multiple detector hybrids, each with a CdTe crystal of 1.1 cm x 2.2 cm x 1 mm, bump-bonded onto a customdesigned application-specific integrated circuit (ASIC). The ERPC ASIC has 2048 readout channels arranged in a 3264 array. Each channel is equipped with pre- and shaping-amplifiers, a discriminator, peak/hold circuitry, and an analog-todigital converter (ADC) for digitizing the signal amplitude. In order to compensate for the pixel-to-pixel variation, two 8-bit DACs are implemented into each channel for tuning the gain and offset. The ERPC detector is designed to offer a high spatial resolution, a wide dynamic range of 12-200 keV and a good energy resolution of 3-4 keV. The hybrid detector configuration provides a flexible detection area that can be easily tailored for different imaging applications. The intrinsic performance of a prototype ERPC detector was evaluated with various gamma ray sources, and the results are presented.

Recently practical X-ray measurement systems are demanded energy distinction function. Photon-counting CdTe semiconductor detectors have a high energy resolution in a low count rate condition at room temperature. However, the energy resolution is decreased by pile-up phenomenon in a high count rate condition. In conventional signal processing, processing time estimated X-ray photon energy from the pulse waveform is about tens of microseconds. This time is depended on the pulse decay time. This paper purposes to maintain the high energy resolution by changing the signal-processing algorithm which derived the pulse rise height of the output waveform from the CdTe detector in a high count rate condition. As a result, the pulse rise time required to estimate the pulse rise height was short about 100ns at incident X-ray energy 60keV. As the result of energy spectrum by using this data, the FWHM of about 11keV (at 60keV) when the count rate of 500kcps. This result show the possibility that the photon counting sensor has application for the high count rate imaging without decrease of the high energy resolution.

Far-infrared (FIR) reflectance spectroscopy has been employed to study the optical properties for a series of bulk CdZnxTe1-x and CdSexTe1-x wafers. The zone-centre optical phonons for the ternary alloys show a variety of behavior patterns: they exhibit a "one-mode", "two-mode" or "intermediate-mode" behavior depending on the vibration characteristics of the end binary members. The CdSeTe called CST were found to be single-crystal with the zincblende structure. These four samples labeled with CST5, CST15, CST25, and CST35, which correspond with the composition of Se, 5%, 15%, 25%, 35%, respectively. The intensity of CdTe-like TO band decays with x increasing, and the peak position increases from 140 cm^-1 to 145 cm^-1. In the other hand, the intensity of CdSe-like TO band grows with x increasing, and the peak position of CdSe-like TO band increases from 174 cm^-1 to 181 cm-1. We use the model of dielectric function and using Least-Square fit to find the optical and transport parameters. By the infrared spectra analysis, we found the conductivity of CdZn_xTe_1-x increase with increasing of x value and the conductivity of CdSe_xTe_1-x decrease with increasing of x value.

CdZnTe or "CZT" crystals are highly suitable for use as a room temperature based spectrometer for the detection and characterization of gamma radiation. Over the last decade, the methods for growing high quality CZT have improved the quality of the produced crystals however there are material features that can influence the performance of these materials as radiation detectors. For example, various structural heterogeneities within the CZT crystals, such as twinning, pipes, grain boundaries (polycrystallinity), and secondary phases (SP) can have a negative impact on the detector performance. In this study, a CZT material was grown by the modified vertical Bridgman growth (MVB) method with zone leveled growth without excess Te in the melt. Visual observations of material from the growth of this material revealed significant voids and SP. Samples from this material were analyzed using various analytical techniques to evaluate its electrical properties, purity and detector performance as radiation spectrometers and to determine the morphology, dimension and elemental /structural composition of one of the SP in this material. This material was found to have a high resistivity but poor radiation spectrometer performance. It had SP that were rich in polycrystalline aluminum oxide (Al₂O₃), metallic Te and polycrystalline CdZnTe and 15 to 50 μm in diameter. Bulk elemental analyses of sister material from elsewhere in the boule did not contain high levels of Al so there is considerable elemental impurity heterogeneity within the boule from this growth.

The synchrotron radiation (SR) X-ray absorption fine-structure spectroscopy (XAFS) technology has been employed to obtained Zn K-edge absorption spectra for Cd1_1-xZn_xTe alloy with x = 0.03, 0.10, 0.20, 0.30, 0.40, 0.50 and 1.00. Their Fourier transform spectra were analyzed, which have shown a bimodal distribution of bond lengths, suggesting distortion of the Te sub-lattice, so that the linear interpolation is true only in an approximate sense. Synthetic CdZnTe crystals can be used for the room temperature-based detection of gamma radiation. The radiation detection properties of CZT crystals vary widely. A common defect found in most high-quality CZT crystals is Te secondary phases, often located along grain boundaries. The secondary phases can be both large inclusions (>50 μm) and smaller precipitates (<50 μm). The Te secondary phases distributed throughout the crystal can cause changes to the detector leakage current, resulting in decreased radiation spectrometer performance. This set of Cd_1-xZn_xTe crystals were also measured by Raman scattering at room temperature. The two observed peaks at about 125 and 145 cm^-1 which can be assigned to Te A₁ and E phonon mode, respectively. The induced damage on the crystal surfaces by Raman laser has been discussed. It is suggested that in the case of highly Zn doping CdZnTe crystals, the ZnTe bond were broken by laser exposing and then free Te atoms are migrating to these heated areas which cause Te precipitate. Further, the results of the soft X-ray measurements have been also presented and this part of the experimental data needs to do more penetrating analysis in the future.

Travelling heater method (THM) has been a great success lately for the growth of large CdZnTe crystals. In this presentation, indium doped CdZnTe crystals have been grown adapting travelling heater method (THM) in vertical configuration, using three zone custom designed muffle furnace. Crystals have been grown with different ampoule diameter and size to study the grain growth. Seedless single crystalline CdZnTe:In crystals have been gown with 4 cm diameter weighing about 650 grams. Crystals have been characterized by near IR imaging, both microscopic and full wafer. The average resistivity along the length of the ingot was found to be about 10⁹ ohm-cm. A resolution 3.2% was obtained at 662 keV. The effect of annealing of the whole wafer in Cd-Zn alloyed vapor on the resistivity and on the Te precipitations will be discussed.

The X- and gamma-ray telescope ECLAIRs onboard the future mission for gamma-ray burst studies SVOM (Space-based multi-band astronomical Variable Objects Monitor) is foreseen to operate in orbit from 2014 on. ECLAIRs will provide fast and accurate GRB triggers to other onboard telescopes, as well as to the whole GRB community, in particular ground-based follow-up telescopes. With its very low energy threshold ECLAIRs is particularly well suited for the detection of highly redshifted GRB. ECLAIRs consists of a X- and gamma-ray imaging camera (CXG) observing in a field of view of 2 sr. The CXG is a 2D-coded mask imager with a 1024 cm² detection plane made of 80 x 80 CdTe pixels, sensitive from 4 keV to 250 keV, with imaging capabilities up to about 50 keV and a localization accuracy better than 10 arcmin. ECLAIRs includes also a triggering electronics which uses the CXG data and detects GRB as countrate increases or the appearance of a new source in cyclic sky images. GRB alerts are transmitted to observers within tens of seconds via a VHF network and all detected photons are available hours later. In this talk we present the lastest ECLAIRs concepts, with emphasis on the expected performances.

The field of ultrafast x-ray science is flourishing, driven by emerging synchrotron sources (e.g., time-slice storage rings, energy recovery linacs, free electron lasers) capable of fine time resolution. New hybrid x-ray detectors are under development in order to exploit these new capabilities. This paper describes the development of a 2160 x 2560 CMOS image sensor (CIS) system with a 6.5 µm pitch optimized for time-resolved x-ray scattering studies. The system is single photon quantum limited from 8 keV to 20 keV. It has a wide dynamic range and can operate at 100 Hz full-frame and at higher frequencies using a region-of-interest (ROI) readout. Fundamental metrics of linearity, dynamic range, spatial resolution, conversion gain, sensitivity and Detective Quantum Efficiency are estimated. Experimental time-resolved data are also presented.

The Advanced GAmma Tracking Array (AGATA) is a next-generation gamma-ray spectrometer for nuclear physics being developed as part of a Europe-wide collaboration. AGATA aims to vastly improve upon the sensitivity of today's arrays by removing the BGO shields used to suppress the Compton background and instead, tracking gamma rays through a complete 4π shell of Germanium using Gamma Ray Tracking (GRT). In order to facilitate this, Pulse Shape Analysis (PSA) must be used to accurately locate the position of each gamma-ray interaction within each detector. The preferred approach to PSA relies on the generation of a database of typical pulse shapes produced by interactions at each position on a grid throughout the detector. This paper details current progress at the University of Liverpool toward validating the electric field simulation, which will be used to generate the pulse shape database, with experimental data from an asymmetric AGATA detector. The field simulation is discussed and some comparisons are made between this and a two dimensional raster scan of the detector with a highly collimated source.

The semiconductor pixel detector Timepix (256 x256 pixels, 55 um pitch) is successor of the Medipix2 device. The detector is adapted for neutrons by deposition of a converter layer onto its surface. Thermal and cold neutrons are converted into heavy charged particles in a layer containing ⁶Li or ¹⁰B. Fast neutrons are detected via protons, again heavy charged particles, recoiled from a polyethylene convertor. The heavy charged particles are detected by the Timepix with submicron spatial resolution. An important advantage of this detection technique is the full suppression of gamma background which is always accompanying experiments with neutrons.

Detection of high-energy neutrons in the presence of gamma radiation background utilizes pulse-shape discrimination (PSD) phenomena in organics studied previously only with limited number of materials, mostly liquid scintillators and single crystal stilbene. The current paper presents the results obtained with broader varieties of luminescent organic single crystals. The studies involve experimental tools of crystal growth and material characterization in combination with the advanced computer modeling, with the final goal of better understanding the relevance between the nature of the organic materials and their PSD properties. Special consideration is given to the factors that may diminish or even completely obscure the PSD properties in scintillating crystals. Among such factors are molecular and crystallographic structures that determine exchange coupling and exciton mobility in organic materials and the impurity effect discussed on the examples of trans-stilbene, bibenzyl, 9,10- diphenylanthracene and diphenylacetylene.

A new, accurate, neutron activation detection scheme for measuring pulsed neutrons has been designed and tested. The detection system is accurate and sensitive to neutrons with energies above 10 MeV; importantly, it is insensitive to gamma radiation and to lower-energy (e.g., fission and thermal) neutrons. It is based upon the use of praesodymium, an element that has a single, naturally occurring isotope (Pr-141), a significant (n,2n) cross section, and decays by positron emission. Neutron fluences are measured by using the sum-peak method to count gamma-ray coincidences from the annihilation of the positron decay product. The system was tested using 14 and 2.45 MeV neutron bursts produced by NSTec Dense Plasma Focus Laboratory fusion sources. Comparisons with lead, copper, beryllium and silver activation detectors have been performed. The detection method allows measurement of 14 MeV neutrons with a total error of ± 10%.

We present significant results in recent advances in the measurement of neutron energy. Neutron energy measurements are a small but significant part of radiological emergency response applications. Mission critical information can be obtained by analyzing the neutron energy given off from radioactive materials. In the case of searching for special nuclear materials, neutron energy information from an unknown source can be of importance. At the Remote Sensing Laboratory (RSL) of National Security Technologies, LLC, a series of materials, viz., liquid organic scintillator (LOS), Lithium Gadolinium Borate (LGB) or Li₆Gd(BO₃)₃ in a plastic matrix, a recently developed crystal of Cesium Lithium Yttrium Chloride, Cs₂LiYCl₆: Ce (called CLYC)^[1], and normal plastic scintillator (BC-408) with 3He tubes have been used to study their effectiveness as a portable neutron energy spectrometer. Comparisons illustrating the strengths of the various materials will be provided. Of these materials, LGB offers the ability to tailor its response to the neutron spectrum by varying the isotopic composition of the key constituents (Lithium, Gadolinium [Yttrium], and Boron). All three of the constituent elements possess large neutron capture cross section isotopes for highly exothermic reactions. These compounds of composition Li₆Gd(Y)(BO₃)₃ can be activated by Cerium ions Ce³⁺. CLYC, on the other hand, has a remarkable gamma response in addition to superb neutron discrimination, comparable to that of Europium-doped Lithium Iodide (⁶LiI: Eu). Comparing these two materials, CLYC has higher light output (4500 phe/MeV) than that from ⁶LiI: Eu and shows better energy resolution for both gamma and neutron pulse heights. Using CLYC, gamma energy pulses can be discriminated from the neutron signals by simple pulse height separation. For the cases of both LGB and LOS, careful pulse shape discrimination is needed to separate the gamma energy signals from neutron pulses. Both analog and digital methods have been applied to obtain a clear gamma and neutron energy spectrum in a mixed radiation field. A waveform digitizer manufactured by Agilent Technology Inc. has been successfully used to digitize the signal and separate the gamma and neutron signals to obtain a high gamma rejection ratio. These results along with some interesting data from a plastic (BC-408) and ³He dual gamma-neuron detector will be presented.

In the area of nuclear radiological emergency response and preparedness applications, interest in neutron detection stems from several factors. Unlike gamma rays, which are abundant in nature and present serious difficulties in differentiating a signal from a changing background, whose values are location specific, neutrons are rare and nearly homogenous in spatial distribution. Additionally, many special nuclear materials (SNM) emit neutrons either directly by spontaneous fission or produce neutrons indirectly through (α, n) reactions in nearby light elements. Also of importance in detection scenarios is the fact that neutrons are not easily attenuated. Typically neutron detection is done by simply counting the low energy thermal neutrons by employing pressurized helium tubes operated at high voltages. Not much emphasis is put on determining the energy of the incident neutrons. However, critical information can be obtained by analyzing the neutron energy given off from radioactive materials. In the detection of an SNM, neutron energy information from an unknown source can be of paramount importance. We have modeled, designed, and prototyped multi-element neutron energy spectrometers that contain three to five pressurized helium tubes of dimensions 2" diam. x 10" in length. Each individual helium tube has a specific amount of high density plastic neutron moderators to slow down the incident energetic neutrons to an accurately estimated energy. A typical spectrometer is a set of moderator cylinders surrounding detectors that have high efficiency for detecting thermal neutrons. The larger the moderator, the higher the energy of incident neutrons for which the detector assembly has matched detection efficiency. If all the detectors are exposed to the same radiation field and the efficiency as a function of energy (response function) of each of the detectors is known, the neutron energy spectrum can be determined from the detector count rates. Monte Carlo simulation results of response function calculations for different arrays of helium tubes with varying amount of moderators will be shown. Experimental evidence of effectiveness of a set of moderated helium tubes to measure the hardness of the incident neutrons will be demonstrated.

In this paper we report the thermal and electronic characteristics of the ternary compound TlGaSe₂, grown from the melt. The phase-diagram, congruency of material and phase transition were studied by differential thermal analysis. The material melted congruently at 812.9C and did not show any other phases between room temperature and the melting point. Results of crystal growth, and effect of alloying and its effect on crystal growth and properties are also discussed. In high purity material it is easier to cleave the crystal since layers of successive rows of tetrahedrons are turned away from each other by 90⁰. However, by suitable alloying, the angle of the tetrahedrons can be changed and the tendency to cleave can be decreased. This effect will be evaluated by comparing the microstructural properties of pure and alloyed crystals. By measuring the optical transmission band edge we studied details absorption characteristics to evaluate the effect of impurities on recombination characteristics. Results indicated that there were no donor-acceptor recombinations at or above room temperature.

We studied two separate as-grown CdMnTe crystals by Infrared (IR) microscopy and Pockels effect imaging, and then developed an algorithm to analyze and visualize the electric field within the crystals' bulk. In one of the two crystals the size and distribution of inclusions within the bulk promised to be more favorable in terms of efficiency as a detector crystal. However, the Te inclusions were arranged in characteristic 'planes'. Pockels imaging revealed an accumulation of charges in the region of these planes. We demonstrated that the planes induced stress within the bulk of the crystal that accumulated charges, thereby causing non-uniformity of the internal electric field and degrading the detector's performance.

TlBr strip detectors with four anode strip electrodes were fabricated in this study. The strip electrodes were formed on TlBr wafers 1 mm thick with a vacuum evaporation process through a shadow mask. Each strip had a width of 0.8 mm and a length of 3.5 mm approximately. The gap between the strips was approximately 0.1 mm. Inter strip resistance more than 1 GΩ was obtained with the process. Energy resolutions of 7.0% and 3.8% FWHM were recorded for 511 keV and 1.33 MeV gamma-rays, respectively, with the TlBr strip detector at room temperature.

Cerium activated rare-earth tri- halides represent a well-known family of high performance inorganic rare-earth scintillators - including the high-light-yield, high-energy-resolution scintillator, cerium-doped lanthanum tribromide. These hygroscopic inorganic rare-earth halides are currently grown as single crystals from the melt - either by the Bridgman or Czochralski techniques - slow and expensive processes that are frequently characterized by severe cracking of the material due to anisotropic thermal stresses and cleavage effects. We have recently discovered a new family of cerium-activated rare-earth metal organic scintillators consisting of tri-halide methanol adducts of cerium and lanthanum - namely CeCl3(CH3OH)4 and LaBr3(CH3OH)4:Ce. These methanol-adduct scintillator materials can be grown near room temperature from a methanol solution, and their high solubility is consistent with the application of the rapid solution growth methods that are currently used to grow very large single crystals of potassium dihydrogen phosphate. The structures of these new rare-earth metal-organic scintillating compounds were determined by single crystal x-ray refinements, and their scintillation response to both gamma rays and neutrons, as presented here, was characterized using different excitation sources. Tri-halide methanol-adduct crystals activated with trivalent cerium apparently represent the initial example of a solution-grown rare-earth metal-organic molecular scintillator that is applicable to gamma ray, x-ray, and fast neutron detection.

Over the last decade the rapid advancements in CCD technology have lead to significant developments in the field of low-light-level, Electron-Multiplying CCDs (EM-CCDs). The addition of a gain register before output allows signal electrons to be multiplied without increasing the external noise. This low effective readout noise, which can be reduced to the sub-electron level, allows very small signal levels to be detected. Caesium iodide is one of the most popular scintillation materials due to its many desirable properties. Approximately 60 photons are produced per keV of incident X-ray or γ-ray with wavelengths peaking at 550 nm (dependent on doping), matching the peak in the quantum efficiency of the back-illuminated CCD97 of over 90%. Using a scintillator coupled to an EMCCD it is possible to resolve individual interactions inside the scintillator. Multiple frames can be taken in quick succession with hundreds of interactions per frame. These interactions can be analysed individually using sub-pixel centroiding and the data compiled to create an image of a much higher resolution than that achieved with a single integrated frame. The interaction mechanism inside the scintillator is discussed with relation to the spatial and spectral resolution of the camera system. Analysis of individual events opens up the possibility of energy discrimination through the profiling of each interaction.

Materials properties important to the design and performance of semiconducting gamma detectors, such as band gap, density, mobility, and crystal cell anisotropy, can depend on similar underlying physics. The resulting property correlations limit the number of design variable and the place effective bounds on the range of physical properties available to gamma-detection materials However, trend correlations can also limit the dependence of error in structure-property relationships and information gaps when considering new candidate materials. Trend analysis complements property estimation via data regression techniques, increasing the generality and certainty of information-based conclusions.

Flexible radiation dosimeters have been produced incorporating thick films (>1 μm) of the semiconducting polymer poly([9,9-dioctylfluorenyl-2,7-diyl]-co-bithiophene). Diode structures produced on aluminium-metallised poly(imide) substrates, and with gold top contacts, have been examined with respect to their electrical properties. The results suggest that a Schottky conduction mechanism occurs in the reverse biased diode, with a barrier to charge injection at the aluminium electrode. Optical absorption/emission spectra reveal a band gap of 2.48 eV for the polymer. The diodes have been used for direct charge detection of 17 keV X-rays, generated by a molybdenum source. Using operating voltages of -10 and -50 V respectively, sensitivities of 54 and 158 nC/mGy/cm³ have been achieved. Increasing the operating voltage shows that the diodes are stable up to approximately -200 V without significant increase in the dark current of the device (<0.2 nA).

Bismuth tri-iodide (BiI₃), a wide band-gap semiconductor, demonstrates many of the material properties necessary for high resolution room temperature gamma-ray spectroscopy. These material properties include high density, large bandgap, and high atomic number. The theoretical intrinsic photopeak efficiency of BiI₃ is approximately 2-3 times higher than CdZnTe over the range of 200-3000 keV. BiI₃ has a theoretical intrinsic photopeak efficiency of 19% at 662 keV, compared to CdZnTe which has a theoretical intrinsic photopeak efficiency of 13% at 662 keV. A modified vertical Bridgman growth method is being used to grow large, greater than 100 mm³, single BiI₃ crystals. Growth parameter optimization has demonstrated that single crystals can be obtained with temperature gradients of 10°/cm or 15o/cm and a growth rate of 0.5 mm/hr, or with a temperature gradient of 10o/cm and a growth rate of 1 mm/hr. Polycrystalline material results from all other growth parameter combinations. X-ray diffraction spectra are used to determine if the crystals are single crystals or polycrystalline. UV-VIS spectra analysis has revealed that the band-gap of BiI₃ is 1.72 eV. The resistivity of the crystals has been determined by generating I-V curves to be on the order of 10⁸-10⁹ Ω-cm. Zone refining is being performed to increase the purity of the starting material and the resistivity of the crystals. Detectors have been fabricated with both gold and palladium electrodes.

The detection of illicit nuclear sources and SNM requires an ubiquitous network of sensors. While ³He proportional counters are excellent neutron detectors, there is an insufficient global supply of ³He to create the required number of detectors. Alternatives to ³He must be efficient, insensitive to gamma radiation, easily manufactured, rugged, and inexpensive to enable the procurement of a large numbers of sensors. The use of a high sensitivity solid-state optical detector coupled to scintillation materials, loaded with a neutron absorber such as ⁶Li or ¹⁰B, can fulfill these design constraints. In this work, we compare the properties of neutron-sensitive scintillation materials utilizing Monte Carlo simulations and experiments. Cs2LiLaBr6:Ce is compared to commercially available boron-loaded plastic scintillators and ³He tubes. The scintillators are compared for neutron detection efficiency, limitations on size, gamma-rejection ratio, neutron detection limits, manufacturing cost, and availability for mass-production.

Informatics-based identification of candidate semiconducting radiation detection materials depends upon the development of a robust knowledge base of materials properties. However, the accuracy and integrity of the knowledge base are often affected by information loss due to incomplete entry and loss of context. We describe our methods for materials property data storage and retrieval, in support of semiconductor development for gamma radiation detection materials informatics applications. Analysis-ready data representations vary with each materials design problem, and are often inconsistent with accurate generic property storage. The proposed approach provides simple, strongly-typed generic storage for as-measured properties, with tools for assessing as-measured properties and converting them to analysis-ready representations. This process simplifies property data stewardship, and allows fine control over the assumptions of data fusion, system characterization, and property representation employed in property-estimation models.

Many materials used in radiation detectors are environmentally unstable and/or fragile. These properties are frustrating to researchers and add significantly to the time and cost of developing new detectors as well as to the cost of manufacturing products. The work presented here investigates the properties of HgS. This material was selected for study based partly on its inherent stability and ruggedness, high density, high atomic number, and bandgap. HgS is found in nature as the mineral cinnabar. A discussion of the physical properties of HgS, experimental characterization of natural cinnabar, and initial radiation detection results are presented along with a discussion of potential crystal growth techniques for producing crystals of HgS in the laboratory.

Amorphous selenium (a-Se) has been widely used as a direct conversion X-ray detection material. Vertical structures are employed in most cases, where >200 μm thick a-Se photoconductor layer is inserted between top and bottom electrodes. In this paper, we design a lateral metal-semiconductor-metal (MSM) structure in which a relatively thin layer of a-Se (~ 8 μm) is coated on top of two lateral electrodes. The simulation results indicate that dark current of such a structure stays extremely low level and external quantum efficiency (EQE) reaches over 30% with wavelengths ranging from 320 to 680 nm. We further fabricate the lateral MSM photoconductor by a two-mask photolithography process. The fabricated photoconductor exhibits a dark current below 40 fA under electric fields ranging from 6 V/μm to 9 V/μm, a responsivity up to 0.06 A/W, a measured EQE of 18% towards a short wavelength of 468 nm, and a high photoresponse speed at 500 Hz with a rise time of 250 μs, fall time of 350 μs, and time constant of 250 μs, respectively. Furthermore, an architecture of indirect conversion X-ray imager is proposed with the use of such a lateral MSM structure and a blue-emitting scintillator material atop.