Cadmium Zinc Telluride

The purpose of this study was to evaluate a small semiconductor-based gamma camera that may have applications in scintimammography. A small cadmium zinc telluride (CZT) detector was evaluated. The detector had a field of view of 20 x 20 cm with detector elements of 2.5 x 2.5 mm in size. Both short-bore (35 mm) and long-bore (50 mm) collimators, matched to the geometry of the detector elements, were evaluated. The imaging performance of the CZT detector was compared with that of a conventional gamma camera equipped with all-purpose and ultra-high-resolution collimators. The performance of both systems with respect to breast imaging was evaluated using a water tank containing small glass spheres, 1.8-9.8 mm in diameter. The effects of variations in breast thickness, tumor depth, and tumor-to-background ratio were all simulated in this phantom model. Total counts per image were adjusted to approximate the count density observed in clinical scintimammographic studies. Sensitivity of the...

We have evaluated 2 small-pixel Cadmium-Zinc-Telluride arrays with thickness of 1 and 2 mm that were fabricated for MSFC by Metorex and Baltic Science Institute. Each array was optimized for temperature and collection bias and was then exposed to Cadmium109, Am241 and Fe55 laboratory isotopes to measure the energy resolution for each pixel. The arrays were then scanned with a

We have developed and constructed an MR-compatible single photon emission computed tomography (SPECT) system for small animal molecular imaging applications. The system consists of identical radiation imaging modules and a multi-pinhole collimator sleeve. The modular design results in a very compact system which allows for easy insertion into state-of-the-art small animal MRI systems. This development leads to a multi-modality system

A method for passivating the surface of Cd1−xZnxTe (CZT) x-ray and gamma ray detectors using relatively simple dry processing techniques has been developed. Leakage currents were significantly reduced for several processing methods. CZT samples were exposed to an oxygen plasma and/or coated with a reactively sputtered silicon nitride layer. Several parameters of the oxygen plasma step were found to be important for achieving enhanced surface resistivity. SiNX has been previously characterized and was used because of its high dielectric quality and low deposition temperature. Reduction in leakage current after passivation by a factor of as much as twenty is demonstrated. Results are also presented which give a measure of the long-term stability of the passivating layers.

Hard X-ray detectors in space are prone to background signals due to the ubiquitous cosmic rays and cosmic diffuse background radiation that continuously bombards the satellites which carry the detectors. In general, the background intensity depends on the space environment as well as the material surrounding the detectors. Understanding the behavior of the background noise in the detector is very important to extract the precise source information from the detector data. In this paper, we carry out Monte Carlo simulations using the GEANT-4 toolkit to estimate the prompt background noise measured with the detectors of the RT-2 Experiment onboard the CORONAS-PHOTON satellite.

Cadmium Zinc Telluride (CZT) detectors are high sensitivity and high resolution devices for hard X-ray imaging and spectroscopic studies. The new series of CZT detector modules (OMS40G256) manufactured by Orbotech Medical Solutions (OMS), Israel, are used in the RT-2/CZT payload onboard the CORONAS-PHOTON satellite. The CZT detectors, sensitive in the energy range of 20 to 150 keV, are used to image solar flares in hard X-rays. Since these modules are essentially manufactured for commercial applications, we have carried out a series of comprehensive tests on these modules so that they can be confidently used in space-borne systems. These tests lead us to select the best three pieces of the ‘Gold’ modules for the RT-2/CZT payload. This paper presents the characterization of CZT modules and the criteria followed for selecting the ones for the RT-2/CZT payload. The RT-2/CZT payload carries, along with three CZT modules, a high spatial resolution CMOS detector for high resolution imaging of transient X-ray events. Therefore, we discuss the characterization of the CMOS detector as well.

Room temperature cadmium zinc telluride (CZT) gamma-ray spectrometers are being developed for a number for years for medical, space and national security applications where high sensitivity, low operating power and compactness are indispensable. The technology has matured now to the point where large volume (several cubic centimeters) and high energy resolution (approximately 1% at 660 eV) of gamma photons, are becoming available for their incorporation into portable systems for remote sensing of signatures from nuclear materials. The straightforward approach of utilizing a planar CZT device has been excluded due to the incomplete collection arising from the trapping of holes and causing broadening of spectral lines at energies above 80 keV, to unacceptable levels of performance. Solutions are being pursued by developing devices aimed at processing the signal produced primarily by electrons and practically insensitive to the contribution of holes, and recent progress has been made in the areas of material growth as well as electrode and electronics design. Present materials challenges are in the growth of CZT boules from which large, oriented single crystal pieces can be cut to fabricate such sizable detectors. Since virtually all the detector grade CZT boules consist of several grains, the cost of a large, single crystal section is still high. Co-planar detectors, capacitive Frisch-grid detectors and devices taking advantage of the small pixel effect, are configurations with a range of requirements in crystallinity and defect content and involve variable degrees of complexity in the fabrication, surface passivation and signal processing. These devices have been demonstrated by several research groups and will be discussed in terms of their sensitivity and availability. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present preliminary results of X-ray measurements on two small format compound semiconductor arrays. The devices, a 5 X 5 gallium arsenide array and a 3 X 3 cadmium zinc telluride array, were produced specifically to address the material, electronic and technological problems that need to be solved in order to develop mega-pixel, Fano limited spectroscopic arrays. The GaAs device

We report progress in the study of thick single-sided charge-sharing cadmium zinc telluride (CZT) strip detector modules designed to perform spectroscopy and 3-D imaging of gamma-rays. We report laboratory measurements including spectroscopy, efficiency and 3-D imaging capability of prototype detectors (15 × 15 × 7.5mm 3 ) with 11×11 unit cells. We also report on Monte Carlo simulations (GEANT4 v7.1) to investigate the effect of multihits on detector performance in both spectroscopy and imaging. We compare simulation results with data obtained from laboratory measurements and discuss the implications for future strip detector designs.

Cadmium Zinc Telluride (CZT) has become a very promising new detector technology for imaging and spectroscopy applications in hard x-ray and gamma ray astronomy. CZT detector technology will enable large area arrays to be built with coded aperture masks for arc second positioning of gamma ray burst sources and for wide-field hard x-ray astronomy. In addition, small CZT detector arrays can be used at the foci of multilayer mirrors for high sensitivity hard x-ray astronomy. This presentation will give an overview of CZT material properties, detector fabrication and testing, detector design and physics, and interconnection of the detector to readout electronics.

We consider the feasibility of closed-loop control to control the interface shape of cadmium zinc telluride (CZT) grown via an electrodynamic gradient freeze (EDG) furnace. A simple proportional control algorithm is applied to a quasi-steady-state model to control the interface shape by adjusting the thermal gradient of the furnace temperatures. Three scenarios are enacted: actuation along the entire external boundary, along the solid portion only, and along the melt portion only. Actuation along the solid only proved to be the most successful of the three scenarios, and produced the unexpected benefit of a favorable convex interface shape.

In an effort to optimize the spectroscopic performance of large volume Cadmium Zinc Telluride (CZT) radiation detectors grown by the Traveling Heater Method (THM), especially for higher energy gamma detection applications, bulk material and pixellated detector performance of THM CZT crystals at 15mm-thick and 10mm-thick were compared to that at 5mm-thick. We demonstrate that the outstanding performance of monolithic pixellated THM CZT detectors was thickness-scalable. For the same monolithic 20× 20 mm 2 “ ...

We have applied several techniques, including photoluminescence, proton-induced x-ray emission, photocurrent, and alpha particle response mapping, for mapping micron- and millimeter-scale variations in cadmium zinc telluride. We have correlated the degree of inhomogeneity determined by these techniques with performance of gamma-ray spectrometers fabricated from the material.

Phoswich detectors (RT-2/S & RT-2/G) are major scientific payloads of the RT-2 Experiment onboard the CORONAS-PHOTON mission, which was launched into a polar Low Earth Orbit of around 550 km on 2009 January 30. These RT-2 instruments are designed and developed to observe solar flares in hard X-rays and to understand the energy transport processes associated with these flares. Apart from this, these instruments are capable of observing Gamma Ray Bursts (GRBs) and Cosmic diffuse X-ray background (CDXRB). Both detectors consist of identical NaI(Tl) and CsI(Na) scintillation crystals in a Phoswich combination, having the same diameter (116 mm) but different thicknesses. The normal working energy range is from 15 keV to 150 keV, but may be extendable up to ~1 MeV. In this paper, we present the RT-2/S and RT-2/G instruments and discuss their testing and calibration results. We used different radio-active sources to calibrate both detectors. The radio-active source 57Co (122 keV) is used for onboard calibration of both instruments. During its lifetime (∼3–5 years), RT-2 is expected to cover the peak of the 24th solar cycle.

We assessed a new dual-energy bone densitometer, the PRODIGY, that uses a narrow-angle fan-beam (4.5 degrees) oriented parallel to the longitudinal axis of the body (i.e., perpendicular to the usual orientation). High-resolution scans across the body can be stepped at 17 mm intervals. The energy-sensitive array detector uses cadmium zinc telluride, which allowed rapid photon counting. Spine and femur scans required 30 s, and total-body scans required 4-5 min; the dose was only 3.7 mrem and 0.04 mrem respectively, or about 5 to 10 times lower than conventional fan-beam densitometry. We found only a small influence of soft-tissue thickness on bone mineral density (BMD) results. There was also a small (+/- 1%) influence of height above the tabletop on BMD results. A software correction for object height allowed a first-order correction for the large magnification effects of position on bone mineral content (BMC) and area. Consequently, the results for BMC and area, as well as BMD, with...