Milano experiment on 0-ν ββ decay of 130Te with a thermal detector

A 73.1 g TeO2 bolometric detector has been operating for more than 4 months at about 16 mK in the Gran Sasso Underground Laboratory. Its energy resolution is comparable with that of a Ge diode. We performed two measurements: without (1389 hours of effective running time) and with (1046 hours) an inner ultra-low activity lead shield of about 3.5 cm in every direction. The energy spectra of thermal pulses show no evidence for 0-ν ββ decay of 130Te. The corresponding 90% c.l. lower limit on the half-life time, 2.7x1021 y, exceeds the value, quoted by geochemical measurements, for the inclusive (2-ν plus 0-ν decay channels) half-life time: 8x1020y. Therefore ββ decay of 130Te has to be attributed mainly to the 2-ν channel. (orig.)