Improvement of high-fold γ-ray data processing: the spherical gate method

A new method for optimizing the processing of events from a highly efficient large array γ-ray detector is described in this article. The spherical gates technique, developed to project high-fold events, consists of optimizing n-dimensional gate shape as a function of peak width and shape of each detector. Formulas in closed form are proposed for determining the projected statistics from coincidence fold and peak shape and for estimating the increased quality of projected spectra. This procedure has been tested on high-fold, high statistics data sets including superdeformed cascades. Compared to the classical “square-gate” technique, better peak-to-background ratios as well as a reduction in fluctuations are observed. A quality parameter is defined to characterize the optimal parameter set. This method leads roughly to a gain in spectral quality equivalent of one fold. It is also shown that the efficiency of the method increases with coincidence fold. This should be particularly suited for future higher-fold data sets. The consequences of a γ-peak profile with a left tailing due to neutron damage is also studied and a method for processing correctly this kind of data is proposed.