Identification of single-site events in germanium detectors by digital pulse shape analysis

A method that discriminates between single- and multiple-site interactions in germanium detectors was developed. For this purpose the output of customary charge-sensitive preamplifiers was differentiated with 10-20 ns sampled with 250 MHz and analyzed off-line. Multiple-site interactions were measured in the 1621 keV photo peak and single-site events in the 1592 keV double escape line of 208Tl. One single parameter describing the broadness of the charge pulse maximum is sufficient to achieve 80% detection efficiencies for both the interaction types, over a wide energy range. As examples, employment of the method in the Heidelberg-Moscow experiment resulted in the consistent half-life of two neutrino double beta decay and the reduction of the background by a factor of three in searches for the neutrinoless double beta decay. Identification of single Compton scattered events improved the minimal detectable activity of a 25% efficiency detector by a factor of two