Year
2006
Abstract
A lightweight, rugged and watertight hand-held instrument has been developed which incorporates a mercuric iodide detector for gamma ray spectroscopy and a helium-3 tube for neutron detection. This instrument uses a planar mercuric iodide detector with a 25 mm x 25 mm contact area and a thickness of approximately 2 mm, which results in an active detection volume larger than 1cm3. Given the physical properties of mercuric iodide, the efficiency is improved compared to the co-planar grid detector used in a similar instrument. In addition, the mercuric iodide detector allows for a wide detectable energy range including the signature of americium which is useful for the detection of plutonium. The spectral analysis is performed using an isotope library incorporated in the instrument. The spectral performance of the mercuric iodide detector has been improved by the use of electronic pulse processing systems, such as a gated integrator and pulse risetime compensation. As a result, the spectral resolution is 2% or better over the energy range of the instrument. The instrument has a large display screen that shows the desired data using a small number of push-button control switches. Representative spectra of selected test sources will be presented and discussed.