Correlation between plastic deformation parameters and radiation detector quality in HgI2

Abstract Mercuric iodide radiation detectors of various grades of quality were subjected to shearing forces in the (001) crystallographic planes using a specially designed micromechanical shear testing fixture. Experimental measurements were made of (001) shear stress versus shear strain. Each of the stress-strain curves was described by two empirically determined deformation parameters, s 0 and σ, where s 0 is a measure of “bulk yielding” and σ indicates the “sharpness of yielding” during plastic deformation. It was observed that the deformation parameters of many HgI 2 single crystal samples fit the relation s 0 = 8σ 2 3 and that significant deviation from this relation, with s 0 > 8σ 2 3 , indicates poor detector quality. Work hardening by prior plastic deformation was also found to cause s 0 to depart (in an increasing manner) from the 8σ 2 3 relation. For good quality material that has not previously been plastically deformed, the deformation parameter s c ≡ s 0 −2 σ