THE EFFECT OF ELEMENTAL AND HYDROCARBON IMPURITIES ON MERCURIC IODIDEGAMMA-RAY DETECTOR PERFORMANCE

Mercuric iodide is a room temperature semiconductor material that is u sed for gamma ray and x-ray radiation detection. Mercuric iodide is sy nthesized from mercuric chloride and potassium iodide and is then puri fied by a series of melts and sublimation steps and by zone refining. The mercuric iodide is grown into crystals and platelets and then fabr icated into detectors. Elemental contamination may be a determining fa ctor in the performance of these detectors. These contaminates may be present in the starting material or may be introduced during, or be un affected by, the purification, growth or fabrication steps. Methods ha ve been developed for the analysis of trace levels of elemental contam ination. Inductively Coupled Plasma/Mass Spectroscopy (ICP/MS), Induct ively Coupled Plasma/Optical Emission Spectroscopy (ICP/OES) and Gas C hromatography/Mass Spectroscopy (GC/MS) are used to determine sub ppm levels of many trace elemental impurities. Trace levels of many elemen tal impurities in the raw mercuric iodide are significantly reduced du ring the purification and zone refining processes. Though the levels o f impurities are reduced, poor performing mercuric iodide detectors ha ve contamination levels remaining or reintroduced which are higher for Ag, Al, Ca, Cu, Mg, Mn, Na, Pb and Zn than detectors with good gamma ray response. This paper will discuss the analytical methodology, the effects of purification on impurity levels, and the correlation betwee n detector performance and impurity levels.