The bolometers as nuclear recoil detectors

Our group is involved in experiments using bolometric detectors since ten years for rare event searches like double beta decay or Dark Matter interactions. During last year, to check the quenching factor of TeO2 bolometers, we have measured the nuclear recoils at energy as low as 15 keV in our experimental apparatus at Laboratori Nazionali del Gran Sasso. Two 72g TeO2 detectors were exposed under vacuum to a Ra-228 alpha source that implanted on them Ra-224 nuclei. The nuclei emitted by the implanted source were detected in one bolometer in coincidence with the corresponding alpha particles in the other. The energy spectrum of the 103.4 keV 224Ra nuclei has been obtained with an energy resolution of about 12 keV. Furthermore an alpha measurement of Roman lead has exploited also the sensitivity of this technique to check for ultralow activity in matter, taking advantage of the source = detector approach. A limit on the Pb-210 contamination in roman lead as low as 4 mBq/Kg has been obtained. (C) 1998 Elsevier Science B.V. All rights reserved.