Characterization of a pixellated CdTe detector with single-photon processing readout

A 1 mm thick pixellated CdTe detector bonded to the MEDIPIX2 [X. Llopart, M.Campbell, R. Dinapole, D. San Segundo, E. Pemigotti, IEEE Trans. Nucl. Sci. NS-49 (5, Part 1) (2002) 2279] readout chip has been characterized using a monoenergetic microbeam at the ESRF. This is an extension of the tests previously reported in Chmeissani et al. [IEEE Trans. Nucl. Sci. NS-51(5) (2004)]. The results show that a full energy peak can be obtained when a narrow beam is focused in the center of the pixel. There is also evidence of significant charge diffusion and fluorescence. The results indicate that the charge sharing is the most important problem and will cause loss of the energy information in an imaging application. The second problem is the fluorescence which limits the number of counts in the full energy peak even for hits in the center of the pixel.