Pulse shape analysis of a segmented planar germanium detector by using the Green's function method and rise-time correlations for depth information

Abstract

We performed pulse shape analysis to extract depth information for an interaction point of gamma rays in a 25-fold segmented germanium detector. With a 90degrees Compton spectrometer with collimators on both incidence and exit sides, we measured pulse shapes for the two interaction points, (x, y, z) = (2.5 cm, 2.5 cm, 0.5 cm) and (2.5 cm, 2.5 cm, 1.0 cm). Experimental pulse shapes were compared with calculated ones by the three-dimensional Green's function method. Analytical solutions for induced charges on each cathode and an anode were obtained for a hole and an electron as a function of time. It is suggested that a rise-time correlation between the anode and the central cathode signals, T-90(anode) - T-50(cathode), can be used as a useful means to determine the depth (z) of an interaction point given an in-plane position (x,y). It is shown that calculated rise-time correlations are in qualitative agreement with experimental ones obtained by uncollimated gamma rays.