Dead layer in living CsI crystal

Abstract

Representations of dead layer (DL) nature in CsI:Na crystals are considered. To eliminate the contradictions between the models of DL, degradation of the conversion efficiency () for surface layers has been studied. Simultaneously, the DL profile and its evolution under aging were studied using X-rays of different energies. It has been shown that immediately after surface polishing the  is increased for 5.9 keV photons (depth of 90% attenuation is equals ~7.6 μm). Anion vacancies are responsible for  increase, whose concentration in the disturbed layer is comparable with the concentration of the activator CA. Decay of supersaturated vacancy solid solution results in extremely inhomogeneous distribution of the  due to the local distortion of the CA. The consequence of this is the disappearance of the full absorption peak in the pulse height spectrum. Despite the loss of energy resolution and detection efficiency (at photopeak) the total counting rate remains constant for -particles. The dead layer itself (the loss of full detection efficiency) is formed after the diffusion of sodium to the free surface, approximately after 6 months and more