Investigation of the behaviour of a mercuric iodide detector under unusual irradiation conditions

A mercuric iodide detector, having an electrode surface 5 × 5 mm2 and a thickness of about 500 μm, was irradiated with a photon beam of 511 keV impinging perpendicularly to the direction of the detector polarisation electric field, that is parallel to the electrodes. In this way the useful thickness for absorption is 5 mm, about ten times greater than in the planar irradiation configuration, where the detector is irradiated through the electrodes along the direction of the electric field. The use of the detector in this configuration allows to achieve a better absorption efficiency for energies up to several hundred keV, without affecting the charge collection efficiency, contrary to the situation when the detector is irradiated in usual configuration (i.e. through the electrodes).