TEO2 BOLOMETERS TO SEARCH FOR DOUBLE BETA-DECAY OF TE-130 - STATUS OFART

A 334g TeO2 crystal is operating since January '93 at Gran Sasso Natio nal Laboratories as a thermal detector to search for neutrinoless beta beta decay of Te-130. The reduction of environmental radioactivity is accomplished by means of a 10 cm thick external lead shielding and a p lexiglas box against Rn-222 , while an inner ultra-low activity lead s hield of at least 3.5 cm in every direction suppresses the residual lo cal radioactivity near the crystal. The good energy resolution and the peak-to-Compton efficiency of the detector allow to understand the ma in features of the residual background. In particular, we are able to reach a sensitivity in the internal contamination of U-238 and Th-232 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. Present limit on neutrinoless betabeta dec ay half-life time of Te-130 obtained with this detector is of the orde r of 10(22)y at 68% C.L., exceeding by one order of magnitude the valu e quoted by the inclusive geochemical measurements, which have therefo re to be attributed mainly to the 2-neutrino channel.