Year
2001
Abstract
Mercuric Iodide is a very promising material for the monitoring of stored materials that can be characterized by the energies and relative intensities of the gamma ray spectra that they produce. The high density and average atomic number of mercuric iodide results in high efficiency compared with other solid-state detectors. In addition, the high resistivity of the material at room temperature makes it possible to produce relatively large detectors with low noise levels at operating biases. Recent technological advances have made it possible to routinely fabricate detector structures of different dimensions tailored to the energy ranges to be investigated. Typical designs have a nominal operating range of 30 - 1300 keV with a spectral resolution of 3% or better at 662 keV. This resolution can be improved by the use of advanced electronics and/or tailored detector design. They have an operating range from less than –20 to 60 degrees Celsius and have stable performance over a wide range of operating conditions over long time scales (> 6 months). The stability, resolution, efficiency, and radiation hardness of these detectors make them ideally suited for unattended monitoring systems either as radiation counters or spectrometers. The detectors are packaged together with a preamplifier in a small, lightweight and rugged \"Mercury\" module that can be used individually or can be incorporated into a larger monitoring system. Several modules can be connected to a common signal processing system so that several locations can be monitored using one spectrum analysis and monitoring system. Spectral data of the detectors will be presented and the electronic layout of the “Mercury” module will be shown. Performance measurements on several representative materials will be shown. Plans for an extended monitoring system to be used in large storage vaults will be presented and discussed.