Ballistic deficit compensation method for a large-volume HPGe detector at high count rates

Abstract

A large-volume HPGe detector normally has a severe ballistic deficit due to its long rise time of the output signals. Despite the trapezoidal shaping algorithm adopted as a remedy to deal with the signals, the algorithm cannot fully eliminate the ballistic deficit in the case of a high counting rate. To resolve the problem, we propose a ballistic deficit compensation method that is based on the measurement of rise time of the signals before shaping. We find that the ballistic deficit after trapezoidal shaping has little relation to the time constant, but shows a quadratic relationship with the rise time and has a negative correlation with the shaping time. In the case of high count rates, the high resolution is handled by fitting the curve to the rise time and the amplitude deficit of the signal after shaping and by compensating for the signal amplitude after trapezoidal shaping. Tests indicate that when the count rate is about 100 kcps, the resolution of Co-60 improves from traditional 2.32 up to 1.91 keV, thus reaching a higher level.