John M. van Scyoc

Role of uniformity and geometry in IMARAD-type gamma-ray spectrometers

We show that the finite size of pixels employed in arrays of the type produced by IMARAD Imaging Systems Ltd. determines the performance of these devices in terms of energy resolution and efficiency. The geometrical considerations are similar to those discussed in the context of small pixels. Based on an understanding of this geometrical effect we show that the performance of the arrays may be optimized for particular device dimensions. In addition we also so that material grown by IMARAD Imaging Systems Ltd. by the modified horizontal Bridgman method is quite uniform and indeed well suited for the fabrication of imaging systems.

Detection of electron and hole traps in CdZnTe radiation detectors by thermoelectric emission spectroscopy and thermally stimulated conductivity

The electric properties of CdZnTe radiation detectors are largely determined by the electron and hole traps in this material. The traps, in addition to degrading the detector performance, can function as dopants and determine the resistivity of the material. Thermoelectric emission spectroscopy and thermally stimulated conductivity are used to detect these traps in a commercially available spectrometer-grade CdZnTe detector, and the electrical resistivity is measured as a function of temperature. A deep electron trap having an energy of 695 meV and cross section of 8 X 10-16 cm(superscript 2

Composition and performance mapping of CdZnTe nuclear spectrometers

is detected and three hole traps having energies of 70 +/- 20 meV, 105 +/- 30 meV and 694 +/- 162 meV are detected. A simple model based on these traps explains quantitatively all the data, including the electrical properties at room temperature and also their temperature dependence.

Orthogonal strip gamma-ray imaging system for use with HgI2 and Cd1-xZnxTe detectors

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.

Uniformity of Cd 1 - x Zn x Te grown by high-pressure Bridgman

We have designed and constructed an orthogonal strip imaging system for use with room temperature semiconductor strip detectors. The system has been tested with both HgI2 and Cd1-xZnxTe (CZT) detector elements. Our first system consists of complete readout electronics and software for spectroscopy and imaging with 8 by 8 orthogonal strip detectors. The readout electronics consist of 16 channels of hybrid charge sensitive preamplifiers, and 16 channels of parallel discriminators, shaping amplifiers, and a 16 channel ADC implemented in CAMAC and NIM. The software used to readout the instrument is capable of performing intensity measurements as well as spectroscopy on all 64 pixels of the device. In this paper we describe measurements to determine the factors limiting the performance of this system.