Year
1994
Abstract
There is a widespread need for light-weight, portable gamma-ray spectrometers suitable for detection of nuclear proliferation, treaty verification, special nuclear materials control, and IAEA-like applications. The detectors should have high energy resolution and sensitivity, and ideally they would be operable at room temperature. A program to characterize and improve the performance of several roomtemperature semiconductor gamma-ray detectors is underway at Sandia National Laboratories, California. The focus of this work is to increase the sensitivity of the devices by increasing the active volume of the detectors. This can be achieved by increasing the mobility-lifetime products of the charge carriers, which will allow for thicker detectors, or by arraying several small detectors to produce a larger detector assembly. The scope of this work has been limited to cadmium zinc telluride (CdZnTe) and mercuric iodide (Hgl2) detectors, because they are two of the most promising candidate materials at this time. Data obtained from single detectors show that the response of independent detectors is slightly different. An electronic scheme is presented to adjust for the different charge induced at the preamp input from the different detectors in the array, so that the response from each detector is identical. This allows a number of small semiconductor detectors to be stacked vertically or horizontally in order to greatly increase the overall system sensitivity. Moreover, the output of each detector can be added prior to the preamp, and multiple preamps are not required. A small amount of unwanted noise does occur due to the increased system capacitance, but this is offset by the increased absorption efficiency of the detector assembly. Nuclear spectroscopic data on horizontal and vertical CdZnTe detector cascades and on thick CdZnTe detectors are presented.