TeO2 bolometers to search for Double Beta Decay of130Te: status of art

A 334g TeO2 crystal is operating since January '93 at Gran Sasso National Laboratories as a thermal detector to search for neutrinoless ββ decay of130Te. The reduction of environmental radioactivity is accomplished by means of a 10 cm thick external lead shielding and a plexiglas box against222Rn, while an inner ultra-low activity lead shield of at least 3.5 cm in every direction suppresses the residual local radioactivity near the crystal. The good energy resolution and the peak-to-Compton efficiency of the detector allow to understand the main features of the residual background. In particular, we are able to reach a sensitivity in the internal contamination of238U and232Th of the crystal of the order of 10−13 g/g, better than that of modern mass spectroscopy methods. Pulse acquisition and analysis techniques are reported and discussed.