Classical solid-state detection of x-ray and gamma-ray radiation consists of a high voltage applied between two metallic contacts sandwiching a high resistivity, high dielectric strength material; high voltage and high resistivity are required to enable complete charge collection while minimizing the resolution-degrading leakage current (dark current). We report here the conception and successful fabrication and test of a new device construct which changes this paradigm. P-type and n-type layers are fabricated by mercury cadmium telluride (HC.T) liquid phase epitaxy (LPE) on opposite sides of a high-quality wafer of CdZnTe (CZT) in order to construct a p-i-n diode structure. Wafers up to 9 cm2 area have been grown. This diode structure provides an extremely high effective resistivity and barrier to the flow of dark current in the device. Several wafer lots have repeatably yielded p-i-n detectors which exhibit typical diode current-voltage (I-V) curves with very low dark currents at very high bias voltages. Spectra obtained from these detectors produce exceptionally sharp photopeaks which exhibit very little low-energy tailing.

Santa Barbara Research Center has developed nuclear radiation testing methodology to measure the performance of IR. detectors in simulated total ionizing dose, transient dose rate (and flux), and neutron environments. The total dose test for IR detectors required that temperature, IR background, bias, and vacuum conditions be maintained and controlled during in-situ measurements of performance parameters; these conditions were accomplished with a specially fabricated Helitrans dewar adapted to a Cobalt-60 internal irradiator. This irradiator and dewar configuration with the appropriate portable measurement equipment allowed I-V and C-V measurements before, during and after irradiation under the same test conditions. This same portable test set was also used to measure detector performance parameters following irradiations with flash X-ray machines. The dose rate test methodology produced consistent detector response and recovery profiles from different X-ray machines at different test facilities. The transient flux test utilized portable equipment including a multichannel analyzer, pulse-shaping amplifier, and a low-noise dewar with built-in amplifier to collect the pulses caused by gamma-flux-induced charge in the detectors. This test was performed at a Cobalt-60 source range which produced a good simulation of the actual environment. The neutron fluence test used portable radiation test equipment and dewars specifically designed to minimize the induced activity expected during irradiation of the detectors for example, in a TRIGA fast-neutron reactor. In this case, the TRIGA reactor core was positioned and shielded in the pool to produce predominantly fast neutrons with an acceptably low level of reactor gammas. The general test methodology, consistent with MIL-STD-883C, provides a capability to test detectors in any ionizing or displacement nuclear radiation type.

Several theories have been offered in explanation of IR spectral differences between powdered enamel and flattened enamel surfaces. This study seeks to expand spectral data relative to powders versus flattened surface planes utilizing large natural mineral fluorapatite (FA) crystals as an experimental model system. Infrared Internal Reflection Spectra were obtained from both powdered FA samples (Durango) as well as from flat surface planes of the same mineral at various angles with respect to crystal orientation. Theoretical considerations together with IRS spectral data using both KRS-5 (n=2.4) and germanium (n=4.0) suggest that optical phenomena may be responsible for observed spectral differences between powdered apatite minerals and faceted planes of identical samples.

THE CHAIRMAN said this was a very important occasion for at least four reasons¿first, there were important people in the audience; secondly, this was the first Paper in the Conference series; thirdly, it was one of the Institution's named Papers; and fourthly, they had a very distinguished speaker. The Institution had sought to bring together for this Session a reasonable balance between the practical and the theoretical. Many people were present who were deeply interested in education, and the Institution itself had the subject very much at heart. Interest in this Paper had been very great and that, together with the fact that there was such a large audience, must be a source of inspiration to Lord Halsbury, who had, in fact, remarked upon the presence of so many people.