Influence of crystal-orientation effects on pulse-shape-based identification of heavy-ions stopped in silicon detectors

Current and charge signals have been collected for Se ions at 408 MeV, S at 160 MeV and Ni at 703 MeV, all stopped in silicon detectors. Some detectors were cut 0 deg off the {111} axis and some off the {100} axis. Important effects on the shape of the silicon current and charge signals have been observed, depending on the orientation of the impinging ion relative to the crystal axes and planes. A degradation of the energy and risetime resolution of about a factor 3 with respect to the measured optimal values (for example 7deg off-axis orientation) is observed for ion impinging directions close to crystal axes and/or planes, i.e. the common scenario for normal incidence on 0deg cut detectors. For Pulse Shape Analysis applications, the necessity of using such ‘‘random’’ oriented silicon detectors is demonstrated.