HIGH-PURITY GERMANIUM DETECTOR IONIZATION PULSE SHAPES OF NUCLEAR RECOILS, GAMMA-INTERACTIONS AND MICROPHONISM

Nuclear recoil measurements with high-purity germanium detectors are v ery promising to directly detect dark matter candidates. The main back ground sources in such experiments are natural radioactivity and micro phonic noise. Digital pulse shape analysis is an encouraging approach to reduce the background originating from the latter. To study the pul se shapes of nuclear recoil events we performed a neutron scattering e xperiment, which covered the ionization energy range from 20 to 80 keV . We have measured ionization efficiencies as well and found an excell ent agreement with the theory of Lindhard. In a further experiment we measured pulse shapes of a radioactive gamma-source and found no diffe rence to nuclear recoil pulse shapes. Pulse shapes originating from mi crophonics of a HPGe-detector are presented for the first time. A micr ophonic noise suppression method, crucial for dark matter direct detec tion experiments, can therefore be calibrated with pulse shapes from g amma-sources. (C) 1998 Elsevier Science B.V. All rights reserved.