This PDF file contains the Front Matter associated with SPIE Proceedings volume 7805, including the Title page, Copyright information, Table of Contents, and Conference Committee listing.

The Travelling Heater Method (THM) for CdZnTe growth is a widely accepted technique for mass production of detector grade material. Compared to other characterizations of THM grown CdZnTe, study of the growth interface has been neglected in the past. In the present report, large grain/single crystalline as-grown detector grade CdZnTe crystals have been grown by THM technique with diameter up to 52 mm. The crystals were grown from Te solution and the structure of the growth interfaces were investigated for both slow cooled and rapid cooled ingots. The macroscopic shape of the interface was studied and correlated with the grain growth of the ingots. A detailed microscopic morphology of the interface was studied in order to investigate the formation of the Te inclusions at the interfaces.

Semiconducting CdZnTe or "CZT" crystals are very suitable for use as a room temperature-based gamma radiation spectrometer. During the last decade, modifications in growth methods for CZT have significantly 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, pipes, voids, 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 in the absence of excess Te in the melt. Numerous SP were imaged using transmission IR at a volume % of 0.002. 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 and good radiation spectrometer performance. It had SPs that were rich in calcium (Ca), carbon (C) and oxygen (O) (possibly CaCO3) or only C and O that were 5 μm or less in diameter.

We present our new results from testing 15-mm-long virtual Frisch-grid CdZnTe detectors with a common-cathode readout for correcting pulse-height distortions. The array employs parallelepiped-shaped CdZnTe (CZT) detectors of a large geometrical aspect ratio, with two planar contacts on the top and bottom surfaces (anode and cathode) and an additional shielding electrode on the crystal's sides to create the virtual Frisch-grid effect. We optimized the geometry of the device and improved its spectral response. We found that reducing to 5 mm the length of the shielding electrode placed next to the anode had no adverse effects on the device's performance. At the same time, this allowed corrections for electron loss by reading the cathode signals to obtain depth information.

Cadmium Zinc Telluride (CZT) has attracted increasing interest with its promising potential as a room-temperature nuclear-radiation-detector material. However, different defects in CZT crystals, especially Te inclusions and dislocations, can degrade the performance of CZT detectors. Post-growth annealing is a good approach potentially to eliminate the deleterious influence of these defects. At Brookhaven National Laboratory (BNL), we built up different facilities for investigating post-growth annealing of CZT. Here, we report our latest experimental results. Cd-vapor annealing reduces the density of Te inclusions, while large temperature gradient promotes the migration of small-size Te inclusions. Simultaneously, the annealing lowers the density of dislocations. However, only-Cd-vapor annealing decreases the resistivity, possibly reflecting the introduction of extra Cd in the lattice. Subsequent Te-vapor annealing is needed to ensure the recovery of the resistivity after removing the Te inclusions.

An approach to the fabrication of CdZnTe-based heterojunction detectors is presented with the primary goal of reducing leakage currents, permitting increased bias voltages and therefore improving x-ray and gamma-ray detector performance. The p-i-n detector architecture is theoretically superior to traditional CdZnTe detectors, and our modeling predicts that superlattice contact layers result in leakage current reductions relative to bulk semiconductor contacts. The benefits arise because the superlattices can be designed to have large carrier effective masses along the electric field direction yet a density of states less than that of a comparable bulk semiconductor.

This work presents a comprehensive study of the Silicon Photomultiplier (SiPM) properties as a novel alternative for radiation detector light sensor. The SiPM low current consumption, its diminutive dimensions and the high gain make this technology of great interest for applications in portable radiation detection instrumentation based on scintillation material. The development progress in investigation of the performance of the device incorporation with CsI(Tl) scintillation crystal during the R&D timeline is presented. The research shows the improvement in two major parameters: the noise level and the resolution. The finding emphasizes that the utilization of the SiPM as the light converting device in radiation sensors is potentially applicable for radiation detection and isotope identification.

Transparent ceramics combine the scintillation performance of single crystals with the ruggedness and processability of glass. We have developed a versatile, scaleable fabrication method, wherein nanoparticle feedstock is consolidated at temperatures well below melting to form inch-scale phase-pure transparent ceramics with optical scatter of α <0.1 cm^-1. We have fabricated Cerium-doped Gadolinium Garnets with light yields of ~50,000 Ph/MeV and energy resolution of <5% at 662 keV. We have also developed methods to form sheets of the high-Z ceramic scintillator, Europium-doped Lutetium Oxide Bixbyite, producing ~75,000 Ph/MeV for radiographic imaging applications.

The effect of high excitation density in promoting nonlinear quenching that is 2^nd or 3^rd order in electron-hole density is generally understood to be a root cause of nonproportionality in scintillators. We report and discuss quantitative data on just how fast these nonlinear channels are in specific cases. Kinetic rate constants for the creation of excitons from electrons and holes and for their quenching by dipole-dipole transfer have been measured in CsI and NaI. We show in addition that the strong radial concentration gradient in an electron track gives rise to fast (~ picoseconds) diffusion phenomena that act both as a competitor in reducing excitation density during the relevant time of nonlinear quenching, and as a determiner of branching between independent carriers and pairs (excitons), where the branching ratio changes along the primary electron track. We use the experimentally measured nonlinear quenching rate constants and values of electron and hole carrier mobilities to carry out quantitative modeling of diffusion, drift, and nonlinear quenching evaluated spatially and temporally within an electron track which is assumed cylindrical in this version of the model. Magnitude and inequality of electron and hole mobilities has consequences for quenching and kinetic order that vary with dE/dx along the path of an electron and therefore affect nonproportionality. It will be demonstrated that in a material with high mobilities like high-purity germanium, Auger recombination is effectively turned off by diffusive carrier dilution within < 1 fs in all parts of the track. In alkali halide scintillators like CsI and CsI:Tl, electron confinement and high-order quenching are accentuated toward the end of a particle track because of hole self-trapping, while separation of geminate carriers is accentuated toward the beginning of the track, leading to 2^nd order radiative recombination and opening additional opportunities for linear trapping.

Energy resolution and detection efficiency were compared between two sizes of cerium bromide (CeBr₃) scintillators, three sizes of lanthanum bromide (LaBr₃:Ce) scintillators, three sizes of sodium iodide (NaI:Tl) scintillators, and a lanthanum chloride (LaCl₃:Ce) scintillator. Comparisons are made of key parameters such as energy resolution, detection efficiency, linearity, and self-activity of CeBr₃, LaBr₃:Ce, LaCl₃:Ce, and NaI:Tl scintillator detectors. The scintillator detectors are tested by comparing the peak separation and identification in the energy range up to 3.0 MeV using ¹³³Ba, ¹⁵²Eu, and naturally occurring radioactive materials [1]. The study has shown that CeBr₃ scintillator detectors provided by Saint-Gobain offer better resolution than NaI:Tl scintillator detectors. CeBr3 detectors could resolve some closely spaced peaks from ¹³³Ba and ¹⁵²Eu, which NaI:Tl could not. LaBr₃:Ce has slightly better resolution, and a slightly higher efficiency than CeBr₃. In this work, "self-activity" of each of these four detector types was measured by operating the detectors themselves. A comparison of the intrinsic activity for all of the detectors in this study is demonstrated. For CeBr₃, the self-activity present may be reduced, or even eliminated in the future, through improved processes for growing the material. It will be discussed if, and under what conditions, CeBr₃ may be better than LaBr₃:Ce and LaCl₃:Ce for detection of certain special nuclear material γ-rays [2]. An overall advantage of CeBr₃ detectors over lanthanum halide and NaI:Tl detectors will be discussed.

Silicon diodes with large aspect ratio perforated microstructures backfilled with ⁶LiF show a dramatic increase in neutron detection efficiency beyond that of conventional thin-film coated planar devices. Described in this work are advancements in the technology with increased microstructure depths and detector stacking methods that work to increase thermal-neutron detection efficiency. Models for ion energy deposition and intrinsic thermal-neutron detection efficiency for the straight trench design are described and results presented. A dual stacked device was fabricated by coupling two detectors back-to-back, along with counting electronics, into a single detector. Experimentally verified results and modeled predictions are compared. The stacked device delivered 37% intrinsic thermal-neutron detection efficiency, lower than the predicted value of 47%. It was determined that this lower observed efficiency is due to detector misalignment in the stacked structure and ballistic deficit from slow charge collection from the deep trench structures. The intrinsic thermal-neutron detection efficiency depends strongly upon the geometry, size, and depth of the perforated microstructures. This work is part of on-going research to develop solid-state semiconductor neutron detectors with high detection efficiencies.

Solid state thermal neutron detectors are desirable for replacing the current ³He based technology, which has some limitations arising from stability, sensitivity to microphonics and the recent shortage of ³He. Our approach to designing such solid state detectors is based on the combined use of high aspect ratio silicon PIN pillars surrounded by ¹⁰B, the neutron converter material. To date, our highest measured detection efficiency is 20%. An efficiency of greater than 50% is expected while maintaining high gamma rejection, low power operation and fast timing for multiplicity counting for our engineered device architecture. The design of our device structure, progress towards a nine channel system and detector scaling challenges are presented.

We have investigated neutron spectrometry using fast gamma-ray detectors (BaF₂) in coincidence with a gamma/neutron detector (plastic scintillator). Neutron spectra of spontaneous fission sources are determined by time-of-flight between correlated gamma and neutron detections using the associated particle (AP) technique. When the source is within a ~1 meter zone of detector separation, the correlated neutron detection efficiency is high because of the multiplicity of gamma-rays (10 gammas/fission in ²⁵²Cf) and neutrons (3.6 neutrons/fission). Cosmic-ray produced neutron detection efficiency is quite low in an AP measurement using a <50ns coincidence window because time-of-flight of most events is long from its creation within the 120 meters e-folding neutron range of air. We found that the AP signal to background ratio was dominated by uncorrelated coincidences and propose a triple coincidence system (1 neutron and 2 gamma-ray detectors) to improve performance. The gamma/gamma-ray coincidence time distribution is related to the target's production history where fast neutron multiplication may be a dominant physical process. MCNPX calculations suggest that the gamma-ray time history of Depleted Uranium (DU) and Highly Enriched Uranium (HEU) provide separable signatures because fast neutron multiplication is much higher in HEU.

In this work we investigated a new method of growing detector grade large GaTe layered chalcogenide single crystals. GaTe ingots (2" in diameter and about 10 cm in length) were grown by a novel method using graphite crucible by slow crystallization from melt of high purity (7N) Ga and Te precursors in argon atmosphere. GaTe samples from the monocrystalline area of the ingot have been cleaved mechanically and characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis by x-rays (EDAX), atomic force microscopy (AFM), xray photoelectron spectroscopy (XPS), transmission line matrix method (TLM), resistivity measurements using van der Pauw technique, Hall Effect and Capacitance-Voltage measurements. Our investigations reveal high potential for developing superior quality GaTe crystals using this growth technique for growing large volume inexpensive GaTe single crystals for nuclear radiation detectors.

In this work, radiation detectors were fabricated using 8 mm × 8 mm substrates, ~ 390 μm in thickness, diced from commercial (0001) 4H-SiC semi-insulating wafer (> 10⁹ Ohm-cm). Our characterization results, including x-ray diffraction (XRD), electron beam induced current (EBIC), chemical etching, cross-polarized imaging, thermally stimulated current (TSC) measurements, chemical etching and Raman spectroscopy, show the high quality of the semiinsulating SiC crystals, which are believed to meet the requirements of fabricating high performance radiation detectors. Current-voltage characteristics showed very low leakage current (~ 1.5 pA at -500 V) and the capability of detector's operation up to 200°C.

We present a novel active and analog readout and preprocessing topology for position sensitive photodetectors (PSPD) that allows to readout a large variety of PSPD devices with different pixel numbers. Additionally, the topology was designed to allow for a significant reduction of analog-to-digital conversion channels. The circuit topology replaces the common passive charge divider and consists of N input stages, N × M weighting stages and M analog adder stages, where N is the number of the input channels, i.e. the number of photodetector pixels and M is the number of outputs. The circuit performs the multiplication of a matrix (the weights) with a vector (signals). For this, the input stage makes M copies of each of the N input signals, the weighting stage multiplies these signal copies with N × M different weights and the output stage adds all weighted copies with the same copy index. For high flexibility, the weights are programmable and the topology allows to interconnect several identical circuits for larger N. Measurements with a first prototype ASIC show that the achieved energy and centroid resolutions equal the resolutions from detectors with passive charge division circuits. However, the presented topology presents important advantages such as scalability. As a first application, we used the prototype ASIC to correct the sensitivity inhomogeneity of position sensitive photomultiplier tubes. As a second application for the circuit, we present a Neural Network based positioning scheme for γ-ray imaging detectors with thick, monolithic scintillation crystals. This allows to correct the strong border artifacts of the center of gravity positioning scheme in monolithic scintillation crystals and thus enhances the spatial resolution of the γ-ray imaging detector.

The Photon 4-dimensional Digital Information (P4DI) ASIC is a new generation of 2D imaging chips to be connected to a pixel sensor using the bump and flip chip technologies. It gives in digital format energy, time and position information for each recorded event. In pixel digitization and storage of the time and amplitude signal are performed. Circuit solutions for gain and offset variation compensation have been implemented. The ASIC works in sparse data scan mode. An 8x8 pixels prototype has been manufactured in UMC 0.18um CMOS technology and evaluated

In this paper we present radiation studies performed on a low-noise, high-speed, largearea CMOS image sensor (CIS) based on the 0.18 μm CMOS process. The sensor has 2560(H) x 2160(V) pixels with a readout speed of 100 frames/sec and a readout noise of less than 2 e- rms. The sensor features 5T pinned photodiode pixels on a 6.5 μm pitch. In order to measure the impact of radiation exposure on the sensor performance, the device was subjected to x-ray exposure of 50 kRads of incident radiation using a broad band 50 KVP x-ray source to assess Total Ionizing Dose (TID) sensitivity. The active area and the digital control block and amplification circuitry were separately irradiated to evaluate the damage to each. Dark data was captured as a function of radiation dose in order to measure dark current and offset changes in the signal.

Improved carrier transport is crucial for enhancing the performance of semiconductor devices such as radiation detectors. Conventionally, semiconductor devices employ planar p-n junctions in which carrier loss occurs mostly in the p-type and n-type diffusion regions. In a nanoscale three-dimensional (3-D) junction, the carriers can be efficiently collected cross the nanostructure by electric field distribution without trapping in the p-n regions. In addition, a nanocone junction should further improve carrier transport properties because this structure can be tailored to be completely depleted. In this work, we studied carrier transport mechanisms in nanojunctions made of vertically aligned ZnO nanostructures and ZnTe matrix using theoretical and experimental methods.

The United States Domestic Nuclear Detection Office (DNDO) Cargo Advanced Automatic Radiography System (CAARS) was an advanced technology demonstration to detect high-Z materials (Z, the atomic number, ≥ 72) in full sized cargo systems such as a 74 foot length tractor-trailer. The L-3 CAARS was one of two CAARS prototypes developed and tested under the program. The L-3 system utilized MeV range dual-energy photons to determine Z and a sophisticated image processing based detection algorithm to accomplish the detection. This paper describes the L-3 CAARS hardware, the physics approach to measuring Z, and presents some results from the system.

The shape of the detectors that comprise a Compton camera largely determines the geometric distribution of the set of data that is measured. It is our hypothesis that the geometric distribution of a set of data determines the informational contents of the data. The objective of the research reported here is to produce evidence that supports this hypothesis. We use a novel approach to measure the informational content of a set of data; namely, we will use the rank of the system matrix, which stems from the data set, as a numerical measure of the informational content of the set. The data was simulated using the surface integral model for Compton camera data. When just the data that scatter parallel to the face of the camera was used, it was found that the resulting system matrix was full rank. When just the data that scatter perpendicular to the face of the camera was used, it was found that the resulting system matrix was substantially less than full rank. Additional work is needed to determine if full rank matrices can be obtained using the conventional camera design that consists of two detectors that are planar shaped and parallel to each other.

Polarized X-ray pulses at 0.6 Å have been generated via head-on collision of a laser pulse from the high-field laser facility at Daresbury with a 30 MeV electron bunch in the ALICE energy recovery linear accelerator. The angular distribution of the backscattered X rays was obtained in single-shot using a scintillation screen. The temporal profile of the X ray yield as a function of the time delay between the laser pulse and electron bunch was measured and agreed well with that expected from the collision point dependence of the laser-electron beam longitudinal overlap.

The Nuclear Compton Telescope (NCT) is a balloon-borne telescope designed to study astrophysical sources of gammaray emission with high spectral resolution, moderate angular resolution, and novel sensitivity to gamma-ray polarization. The heart of NCT is a compact array of cross-strip germanium detectors allowing for wide-field imaging with excellent efficiency from 0.2-10 MeV. Before 2010, NCT had flown successfully on two conventional balloon flights in Fort Sumner, New Mexico. The third flight was attempted in Spring 2010 from Alice Springs, Australia, but there was a launch accident that caused major payload damage and prohibited a balloon flight. The same system configuration enables us to extend our current results to wider phase space with pre-flight calibrations in 2010 campaign. Here we summarize the design, the performance of instrument, the pre-flight calibrations, and preliminary results we have obtained so far.

A prototype molecular imaging system that features wide-band imaging capability from 100 keV to MeV was developed based on a germanium Compton camera. In this system, radiotracer imaging is performed through the Compton imaging technique above 300 keV and through the coded mask imaging technique below 200 keV. For practical use, small animal imaging requires spatial resolution of the order of millimeters. We conducted tests with a multiple-well phantom containing ^99mTc (140 keV) and ⁵⁴Mn (834 keV), and confirmed the spatial resolution of better than 3.2 mm for the phantom placed 35 mm above the detector. We also report imaging results of a living mouse into which we injected ^99mTc (140 keV) and ⁵⁴Mn (834 keV).

Dead time in detectors limits the capability of the detector to work at high counting rates. A correction for dead time can be used to estimate the particle flux from a measurement. A motivation for operating detectors at high counting rates is to get the best statistical accuracy. It is therefore also important to correct measurements for the loss of statistical accuracy that occurs when dead time is present. When the source of particles has a time dependent variation in intensity, the conventional dead time correction may not apply. A new dead time correction that applies in this case is presented.

Charge transport mechanism responsible for leakage current in X/γ-ray detectors with a p-n junction formed in semi-insulating p-like CdTe single crystals by laser-induced doping is studied. The In/CdTe/Au diodes showed high rectification and good spectral response to high-energy radiation, however samples were suffering from an increase in leakage current and deterioration of the characteristics with time. The proposed energy diagram allows to explain the reverse I-V characteristic of the diodes. At low voltages, the Sah-Noyce-Shockley theory describes well both the shape of the I-V characteristic and its temperature changes. At higher voltages, measured currents deviate from the theoretically calculated values toward increasing. An additional current increase is attributed to injection of electrons from the "near-ohmic" Au/CdTe contact and their diffusion to the p-n junction. When the current increases, the drift component is also included in injection of electrons. This leads to a rapid rise in the current contribution with increasing bias voltage and limits possibility to extend the detector active region by increasing the applied voltage.

Conventional gamma cameras which uses photomultiplier tubes(PMT) is very heavy, bulky, and expensive. In addition, its spatial resolution is low because of geometrical limitation of PMTs. This low resolution and large size is not efficient for the small animal imaging system which is useful in preclinical imaging application. We have developed a small size but high spatial resolution gamma ray detector, based on charge-coupled device(CCD) which is useful to develop a prototype model of small animal gamma camera. Recently the sensitivity of CCD was improved and the peltier cooling system helped to minimize the dark currents of CCD significantly. The enhanced sensitivity and high intrinsic resolution of CCD enabled researchers to develop the small size gamma camera with low cost. In this study we used peltier cooled CCD sensor which has about 70% of quantum efficiency at 650nm wave length. CsI(Tl) scintillator was also used to convert the gamma ray to visible lights. These light photons from the scintillator have been collected to the CCD surface by Nikorr macro lens to enhance the collection efficiency. The experimental results showed that the proposed CCD-based detection system is feasible for gamma ray detection.

Bulk Cd_1-xZn_xTe (0<x<0.1) single crystals for gamma-ray detectors are grown mainly from nearstoichiometric melts. We discuss the influence of the thermal pre-history of the melts (superheating, thermo-cycling, and cooling rate) on various physical properties based on our thermographic analyses, electrical conductivity and viscosity measurements. Increasing the Zn content causes non-monotonic dependencies in the quality of the crystals' structure.

Spectrometers must have the ability to identify Special Nuclear Materials (SNM) that may be present, even if hidden and masked by naturally occurring radioactive materials) NORM). Prediction of the g spectrum is vital to recognize the different combinations, as the shape is determined by absorption and geometrical factors . A program was developed, which utilizes geometric equations and detector characteristics data to produce the synthetic gamma-ray spectra. The program is a convenient tool to check the compliance of the spectrometers to the requirements concerning the identification of different isotopes combinations.

In this study 2-dimensional plasma simulation code was used to find a new approach of x-ray detection method with PDP-like geometry and condition. A conventional PDP geometry consisted of three electrodes was selected and Ne-Xe composition gas was filled the cell-gap. Depending on incident X-ray energy, the number of charges generated within the cell-gap could be different. For the charge amplification and collection of charges two consecutive ac pulses were applied to scan and address electrodes. The increased charges were collected on the positive-bias address electrode at the rear panel. Two parameters, such as amplitude of collected current and formation delay of collected current, were calculated and compared. The formation delay showed more accurate relationship than the collected current amplitude.

PIN diodes for digital X-ray detection as a single photon counting sensors were fabricated with a guard ring structure with p+ doping for reducing the leakage current. The efficiency of the guard ring was verified by significantly reduced leakage current compared to the Si-PIN diodes without guard ring structure and the gap distance between the active area and the guard ring was optimized as the leakage currents showed strong dependency on it. In this paper, secondary ion mass spectroscopy (SIMS) profile was measured and characterized to investigate potential process improvement. Since a large transient enhanced diffusion (TED) as the broadening of 200 nm at the tail is observed in the boron SIMS profile, it is suggested to reduce the annealing process time of RTA or to use spike annealing process. Also, in order to investigate the effect of reduced TED or other possible process to achieve shorter junction depth for improving device performance, it is in progress to fully optimize the process simulation incorporating the transient enhanced diffusion model of boron in Si.

The temperature dependences of the resistivity of detector-grade semi-insulating CdTe and Cd_0.9Zn_0.1Te single crystals were investigated. The investigations have revealed that the thermal activation energy can be higher than E_g/2 at T → 0 K or considerably less than this value, although the Fermi level is located near the middle of the band gap. It is shown that such an "anomalous" behavior of the electrical characteristics is explained in detail by the features of the compensation of deep acceptor levels in the semiconductor band gap. A method based on the electroneutrality equation is proposed for the determination of the ionization energy and compensation degree of the impurity (defect), which is responsible for the conductivity of the material. The results extracted with the use of this method lead to the prediction that the inversion of the conductivity type of the semiconductor under certain conditions can occur as the temperature varies during operation of a Cd(Zn)Te-based device.

Cadmium telluride (CdTe) detector has been used to detect thermal neutrons; along with gadolinium (Gd) used as a neutron converter. Simulation results show that the appropriate thickness of Gd film for CdTe detector is 25 μm. The Gd/CdTe detector shows the 80 keV, 89 keV and 182 keV gamma ray emission peaks from ¹⁵⁵Gd(n, γ)¹⁵⁶Gd and ¹⁵⁷Gd(n, γ)¹⁵⁸Gd reactions.

To identify the factor impairing the material identification parameters, which is provided by the dual-energy X-ray computed tomography method using a conventional X-ray tube and a CdTe detector, linear attenuation coefficient was measured by the radioactivity of radio isotopes and compared with theoretical figure. In our study, the atomic number and the electron density is calculated from the linear attenuation coefficient obtained in CT measurement by 64-channel CdTe line detector. To estimate accuracy of CdTe line sensor, it is needed to obtain the linear attenuation coefficient accurately. Using a single detector, the linear attenuation coefficient is verified for accuracy. The energy resolution of CdTe detectors and the method of reconstruction are discussed.

We characterized samples cut from different locations in as-grown CdZnTe (CZT) ingots, using Automated Infrared (IR) Transmission Microscopy and White Beam X-ray Diffraction Topography (WBXDT), to locate and identify the extended defects in them. Our goal was to define the distribution of these defects throughout the entire ingot and their effects on detectors' performance as revealed by the pulse-height spectrum. We found the highest- and the lowest- concentration of Te inclusions, respectively, in the head and middle part of the ingot, which could serve as guidance in selecting samples. Crystals with high concentration of Te inclusions showed high leakage current and poor performance, because the accumulated charge loss around trapping centers associated with Te inclusions distorts the internal electric field, affects the carrier transport properties inside the crystal, and finally degrades the detector's performance. In addition, other extended defects revealed by the WBXDT measurements severely reduced the detector's performance, since they trap large numbers of electrons, leading to a low signal for the pulse-height spectrum, or none whatsoever. Finally, we fully correlated the detector's performance with our information on the extended defects gained from both the IR- and the WBXDT-measurements.

Development and studies of characteristics are reported for X-ray radiation detectors of "scintillator-photodiode" type showing improved spatial resolution with photosensitive area step of 1.6, 0.8, 0.4 and 0.2 mm and number of channels 16, 32, 128 and 256, respectively. The receiving-detecting channel has been adjusted and tested, appropriate software has been developed, and shadow X-ray images of tested objects were obtained. Evaluations were made of spatial resolution, resolution over thickness and detecting ability of the digital radiographic sysyem based on the detector array. Recommendations are formulated on application of such devices for non-destructive testing and technical diagnostics. Further studies on obtaining two-energy images show possibilities of substantial broadening of the application fields of the digital radiographic system, allowing determination of the effective atomic number Z_eff for component substances of the tested objects. A possibility is shown of substance discrimination by their effective atomic number even for "light" elements with Z_eff from 6 to 13. Clear distinction could be observed between such substances as water (H₂O) with Z_eff≈7.43 and glycerol (CH₂OHCHOHCH₂OH) with Z_eff≈ 6.87.

We report on progress to develop and demonstrate CZT and Si hybrid detector arrays for future NASA missions in X-ray and Gamma-ray astronomy. The primary goal for these detectors is consistent with the design concept for the EXIST mission¹ and will also be appropriate for other NASA applications and ground-based projects. In particular we target science instruments that have large aperture (multiple square meters) and therefore require a low power ROIC (readout integrated circuits) design (< 10 microwatt per pixel in quiescent mode). The design also must achieve good energy resolution for single photon detection for X rays in the range 5-600 keV with a CZT sense layer and 2-30 keV with a Si sense layer. The target CZT arrays are 2 cm × 2 cm with 600 micron square-shaped pixels. The low power smart pixel detects rare X-ray hits with an adjustable threshold setting. A test array of 7 × 5 pixels with a 5 mm thick CZT sense layer demonstrates that the low power pixel can successfully detect X-rays with ~50 readout noise electrons RMS.

This paper presented a new carrier board attachment method for pixellated CdZnTe (CZT) radiation detectors by using a special type of anisotropic conductive film (ACF) based on micro-wires. This ACF has very small pitch, high vertical electrical conductivity, and strong mechanical strength. It was found to be suitable for pixellated CZT detector assembly by optimizing detector fabrication processes and attachment conditions. ACF attached detector modules showed excellent spectra responses. Long-term stability and reliability tests on these detectors showed promising results. This ACF attachment technology had been successfully used for pixellated CZT detectors with various physical dimensions and anode pixel patterns.

Dark currents, including those in the surface and bulk, are the leading source of electronic noise in X-ray and gamma detectors, and are responsible for degrading a detector's energy resolution. The detector material itself determines the bulk leakage current; however, the surface leakage current is controllable by depositing appropriate passivation layers. In previous research, we demonstrated the effectiveness of surface passivation in CZT (CdZnTe) and CMT (CdMnTe) materials using ammonium sulfide and ammonium fluoride. In this research, we measured the effect of such passivation on the surface states of these materials, and on the performances of detectors made from them.

We have developed a prototype of a scalable high-resolution direction and energy sensitive gamma-ray detection system that operates in both coded aperture (CA) and Compton scatter (CS) modes to obtain optimal efficiency and angular resolution over a wide energy range. The design consists of an active coded aperture constructed from 52 individual CZT planar detectors each measuring 3×3×6 mm³ arranged in a MURA pattern on a 10×10 grid, with a monolithic 20×20×5 mm³ pixelated (8×8) CZT array serving as the focal plane. The combined mode is achieved by using the aperture plane array for both Compton scattering of high-energy photons and as a coded mask for low-energy radiation. The prototype instrument was built using two RENA-3 test systems, one each for the aperture and the focal plane, stacked on top of each other at a distance of 130 mm. The test systems were modified to coordinate (synchronize) readout and provide coincidence information of events within a user-adjustable 40-1,280 ns window. The measured angular resolution of the device is <1 deg (17 mrad) in CA mode and is predicted to be approximately 3 deg (54 mrad) in CS mode. The energy resolution of the CZT detectors is approximately 5% FWHM at 120 keV. We will present details of the system design and initial results for the calibration and performance of the prototype.

Gamma-ray spectroscopic systems with high efficiency and energy resolution have become important in many fields. Conventional systems with analog shaping are more and more replaced by digital systems that can provide higher throughput, better energy resolution and better stability. We present the development of our new versatile real time Multi Channel Analyzer with digital signal processing, the GMCA. The device has two independent channels and is compatible with various detectors like Coplanar Grid (Cd,Zn)Te, HPGe, LaBr3, NaI and CsI. Different sensors for temperature, pressure and humidity provide additional information and allow the correction of thermal drifts. We show energy resolution measurements and compare spectra measured with different detectors connected to our system and to commercial systems both analog and digital.

We have been working on the development of a detector design for a large area coded aperture imaging system operating in the 10-600 keV energy range. The detector design is based on an array of Lanthanum Bromide (LaBr₃) scintillators, each directly coupled to a Hamamatsu 64-channel multi-anode photomultiplier tube (MAPMT). This paper focuses on the development of the GEANT4-based simulations as an aid in the optimization of the detector design. The simulations have been validated by comparisons with various laboratory data sets. We will summarize the current status and latest findings from this study.