GAMMASPHERE: Elimination of ballistic deficit by using a quasi-trapezoidal pulse shaper

Gammasphere uses an spherical array of very large (7.2cm dia.) germanium detectors and only high-multiplicity events are studied. To achieve a reasonable coincidence rate, the individual detector channels must handle high rates with minimum pile-up losses. Ten microseconds was chosen as the total processing time for a signal which means that the shaped signal peaks in about 4us. The combination of short pulse shaping and the fluctuating long charge collection times (up to 400ns) in the detectors exaggerates the energy resolution degradation due to ballistic deficit effects. We describe a method of producing a flat-topped pulse with a simple time-invariant network that satisfies GAMMASPHERE requirements and eliminates ballistic deficit effects