The hard X-ray response of HgI2

We summarise the results of a number of X-ray measurements on a 7 mm2, 0.5 mm thick HgI2 detector carried out both in our laboratory and at two synchrotron radiation facilities in Germany. The detector energy response function was found to be linear over the energy range 2.3–100 keV with an average rms non-linearity of 0.2%. Using a 50×50 μm2 15 keV monoenergetic X-ray beam, the spatial uniformity of the detector response was determined by a raster scan technique to be better than 1%. At room temperature, the FWHM energy resolution was 600 eV at 5.9 keV rising to 6 keV at 100 keV with no statistically significant difference between pencil beam (50×50 μm2) and full-area illumination. It was found that the FWHM energy resolution decreased with decreasing temperature reaching a minimum of 400 eV for 5.9 keV X-ray illumination at −19.2°C. Below this temperature, the FWHM begins to rise slowly. By considering the various contributions to the FWHM energy resolution, we estimate the charge collection efficiency to be (95.2±0.7)% at room temperature and (98±0.2)% at −19°C with a Fano factor of 0.30±0.24 at room temperature.