Non-uniformity of light output in large-sized CsI(Tl) crystals grown by non-vacuum Bridgman method

CsI crystals doped with different concentration of Tl were grown with non-vacuum Bridgman method, so-called as the modified Bridgman method. The dependence of the light output on Tl content was studied and 1000 ppm (mol) of TlI was suggested as a suitable doping level for growing large CsI(Tl) crystals with this crystal growth technique. The distribution of thallium along the longitudinal direction of the CsI crystal was analyzed by the Atomic Absorption Spectrometry (AAS) and has been proved to be inhomogeneous. The non-uniformity of light output along the longitudinal axis of a large crystal with dimension of 80×80×400 mm3 was rather evident, however, it could be amended, during the mechanical processing of the boule, by properly defining one of the end faces (tail side) as the particle incident face, named as front face, and another end face (seed side) for attached by PMT or photodiode to be named as rear face. The influence of irradiation on the non-uniformity of light output was investigated as well.