UC Berkeley

We present the performances of two 92% enriched ¹³⁰TeO2 crystals operated as thermal bolometers in view of a next generation experiment to search for neutrinoless double beta decay of ¹³⁰Te. The crystals, 435 g each, show an energy resolution, evaluated at the 2615 keV γ-line of ²⁰⁸Tl, of 6.5 and 4.3 keV FWHM. The only observable internal radioactive contamination arises from ²³⁸U (15 and 8 μBq/kg, respectively). The internal activity of the most problematic nuclei for neutrinoless double beta decay, ²²⁶Ra and ²²⁸Th, are both evaluated as <3.1 μBq/kg for one crystal and <2.3 μBq/kg for the second. Thanks to the readout of the weak Cherenkov light emitted by β/γ particles by means of Neganov–Luke bolometric light detectors we were able to perform an event-by-event identification of β/γ events with a 95% acceptance level, while establishing a rejection factor of 98.21% and 99.99% for α particles.