Ionization measurement at very low temperature for nuclear and electron recoils discrimination by ionization-heat simultaneous measurement for dark matter research

To achieve a high level of discrimination between nuclear recoils and elect ron recoils for dark matter research, we realized and studied ionization-he at detectors working at very low temperature (10-20 mK). To understand the mechanisms underlying the ionization measurement at this temperature range, we made systematic studies of detectors performances (time stability, ener gy resolution, etc.) in X- and gamma-rays detection for Ge and Si detectors . Results are presented and discussed. We found that the time stability is governed by the progressive space charge build-up due to impurities ionizat ion by far-infrared radiation. Moreover if the energy resolution of HPGe-pi n detectors is limited by the noise, it appears to be intrinsically limited by carrier trapping on neutral impurities in Si detectors. (C) 2000 Elsevi er Science B.V. All rights reserved.