Parallel pulse processing for mercuric iodide gamma-ray detectors

Mercuric iodide (HgI2) is a semiconductor material of interest for use as a gamma ray detector because of its wide band-gap and high atomic number. The current work is with detectors of intermediate thickness (2 to 5mm), to be used to get good energy resolution with some reasonable gamma ray efficiency. The work reported covers the parallel pulse processing to obtain interaction depth information which is used to extend the usable thickness through resolution enhancements, and to obtain better detector performance from selected portions of the thicker detectors through pulse rejection techniques. A sample spectrum from a 2.5-mm-thick detector is shown. Resolution is about 10% and peak-to-valley ratio about 4:1. After taking advantage of the enhancement techniques described, resolution of 5% and peak-to-valley ratios of 8:1 are common. Poor hole mobility has been used to advantage to obtain interaction depth information. Two techniques are demonstrated for extracting conventional energy spectra from two-parameter spectra - the spectral enhancement technique which corrects for hole losses in every interaction in the detector and increases the number which fall under the full energy peak, and the pulse rejection technique which selects only those pulses which need no correction.