Noise reduction for proportional counter signals in the GNO solar neutrino experiment

The GALLEX solar neutrino experiment as well as the follow-up experiment GNO are low-level, low-statistics experiments with a mean production rate of 0.7 71Ge atoms per day by neutrino capture on 30.3 t of natural gallium. This is a challenge with respect to the long time stability of the whole equipment, especially the stability of the electronic components which acquire the signals of the 71Ge decay events in proportional counters. Approximately, every month a sample of about ten 71Ge atoms (half-life 11.4 d) is typically measured in the GALLEX and GNO experiments for a period of half a year. The background is minimized by low-level techniques. In addition, 71Ge decays are distinguished from background events by pulse shape analyses. The background rejection efficiency is directly correlated with the signal to noise ratio of the recorded events. A method is described which increases the signal to noise ratio of the acquired ionization events and allows to distinguish between detector signals and noise picked up from the detector environment. This method can be applied not only for proportional counters but also for many other detectors.