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The ''Radiation continuity Checker'', an Instrument for Monitoring Nuclear Disarmament Treaty Compliance

Description: We describe the design, construction and performance of an instrument designed to monitor compliance with future arms control treaties. By monitoring changes in the gamma-ray spectrum emitted by a stored nuclear weapon, our device is able to sense perturbations in the contents of a weapon storage container that would indicate treaty non-compliance. Our instrument (dubbed the Radiation Continuity Checker or RCC) is designed to detect significant perturbations in the gamma-ray spectra (indicative of tampering) while storing no classified information about the weapon, and having a negligible ''false alarm rate''. In this paper we describe the technical details of two prototype instruments and describe the strategies we have adopted to perform signal processing in these instruments. Our first instrument prototype uses a scintillation spectrometer and a massive tungsten alloy collimator to reject the gamma-ray background. Our second prototype instrument makes use of an active collimation scheme employing a multiple detector Compton scatter approach to reject background radiation. The signal processing method we employ uses linear algorithms applied pulse by pulse. This eliminates the need for storage of pulse height spectra, which are in many cases classified.
Date: October 1, 2000
Creator: Bernstein, A.; Brunett, B. A.; Hilton, N. R.; Lund, J. C. & Scyoc, J. M. Van
Partner: UNT Libraries Government Documents Department

Spatial Mapping of Cadmium Zinc Telluride Materials Properties and Electrical Response to Improve Device yield and Performance

Description: Cadmium zinc telluride has experienced tremendous growth in its application to various radiation sensing problems over the last five years. However, there are still issues with yield, particularly of the large volume devices needed for imaging and sensitivity-critical applications. Inhomogeneities of various types and on various length scales currently prevent the fabrication of large devices of high spectral performance. This paper discusses the development of a set of characterization tools for quantifying these inhomogeneities, in order to develop improvement strategies to achieve the desired cadmium zinc telluride crystals for detector fabrication.
Date: January 26, 1998
Creator: Scyoc, J. M. Van; Brunet, B. A.; Yoon, H.; Gilbert, T. S.; Hilton, N. R.; Lund, J. C. et al.
Partner: UNT Libraries Government Documents Department

Low-cost cadmium zinc telluride radiation detectors based on electron-transport-only designs

Description: The goal of this project was to utilize a novel device design to build a compact, high resolution, room temperature operated semiconductor gamma ray sensor. This sensor was constructed from a cadmium zinc telluride (CZT) crystal. It was able to both detect total radiation intensity and perform spectroscopy on the detected radiation. CZT detectors produced today have excellent electron charge carrier collection, but suffer from poor hole collection. For conventional gamma-ray spectrometers, both the electrons and holes must be collected with high efficiency to preserve energy resolution. The requirement to collect the hole carriers, which have relatively low lifetimes, limits the efficiency and performance of existing experimental devices. By implementing novel device designs such that the devices rely only on the electron signal for energy information, the sensitivity of the sensors for detecting radiation can be increased substantially. In this report the authors describe a project to develop a new type of electron-only CZT detector. They report on their successful efforts to design, implement and test these new radiation detectors. In addition to the design and construction of the sensors the authors also report, in considerable detail, on the electrical characteristics of the CZT crystals used to make their detectors.
Date: January 1, 1999
Creator: Brunett, B. A.; Lund, J. C.; Scyoc, J. M. Van; Hilton, N. R.; Lee, E. Y. & James, R. B.
Partner: UNT Libraries Government Documents Department

Fine-scale spatial response of CdZnTe radiation detectors

Description: Several studies have suggested that the uniformity of Cadmium Zinc Telluride (CZT) detectors play an important role in their performance when operated as gamma-ray spectrometers. However the detailed gamma response of simple planar detectors as a function of position over the device area is largely unknown. To address this issue the authors have built a system capable of measuring the detector response with a resolution of {approximately}250 {micro}m. The system consists of a highly collimated ({approximately}200 {micro}m) photon source (<150 kev) scanned over the detector using a computer controlled two-axis translation stage. Fifteen samples configured as planar detectors were examined with the new apparatus. The material grade of the detectors examined varied from counter to select discriminator. Two classes of spatial response variation were observed and are presented here. Infrared (IR) transmission images were also acquired for each sample and correlation between features in the pulse height spectrum and crystalline defects were observed.
Date: November 7, 1998
Creator: Brunett, B. A.; Scyoc, J. M. Van; Hilton, N. R.; Lund, J. C.; James, R. B. & Schlesinger, T. E.
Partner: UNT Libraries Government Documents Department

Multi-parameter high-resolution spatial maps of a CdZnTe radiation detector array

Description: Resistivity results from a 48x48 pixelated CdZnTe (CZT) radiation detector array are presented alongside X-ray topography and detector mapping with a collimated gamma-ray beam. By using a variety of measurements performed on the same sample and registering each data set relative to the others, the spatial dependence of relationships between them was examined. The local correlations between resistivity and one measure of detector performance were strongly influenced by the positions of grain boundaries and other gross crystal defects in the sample. These measurements highlight the need for material studies of spatially heterogeneous CZT to record position information along with the parameters under study.
Date: November 7, 1998
Creator: Hilton, N. R.; Barber, H. B.; Brunett, B. A.; Eskin, J. D.; Goorsky, M. S.; James, R. B. et al.
Partner: UNT Libraries Government Documents Department