Side effects of the use of cylindrical grooves in planar intrinsic germanium detectors

Abstract

One technique for producing planar intrinsic germanium detectors involves machining a deep groove in the detector crystal just inside the outer cylindrical surface and running from one plane face almost to the other. Weak collection fields near the base of the groove can then be expected to lead to the appearance of some output pulses having very long rise times. Two detectors of this type have been examined. It was found that at low counting rates and in the absence of pulse shape discrimination slowly rising pulses were processed as if they formed a continuum of low energy pulses extending into regions where with a mono-energetic gamma source pulses would not normally be present. At high counting rates the smallest slow pulses, which escape the attention of the pile-up detection circuits, were found to give rise to lines with high energy tails, and to excess rate dependent line broadening.