Crystal perfection of HgI2 studied by neutron and gamma-ray diffraction

Abstract

The crystalline perfection of wire sawn pieces of vapor grown single crystals of mercuric iodide was compared with the perfection of (00l) cleaved sections of the same crystal from which nuclear radiation detectors have been fabricated. The crystalline perfection was studied using neutron and gamma‐ray diffraction rocking curves. Most of the gamma‐ray data were obtained using a high intensity source of ¹⁵³Sm gamma rays with a wavelength of λ = 0.12 Å. Some of the data were obtained using highly penetrating ¹⁹⁸Au gamma rays with a shorter wavelength of λ = 0.03 Å. The neutrons had a wavelength of λ = 1.07 Å. It was found that, in terms of the mosaic spread of the crystals, the cleaved detector plates have a much lower crystalline perfection than the thicker uncleaved detector plates. At the same time, the results show that for detectors cut from the same crystal, the one with the lower spectral resolution for radiation detection will also have a lower perfection and larger width of the gamma‐ray rocking curve. These results suggest consideration should be given to alternative fabrication procedures for HgI₂ nuclear radiation detectors.