UC Berkeley

The Cryogenic Underground Observatory for Rare Events (CUORE) is an experiment that will search for neutrinoless double-beta (0&nu&beta&beta) decay of ¹³⁰Te and other rare processes. Observing 0&nu&beta&beta decay would establish that neutrinos are massive Majorana fermions, demonstrate that lepton number is not conserved, and constrain the neutrino mass scale and hierarchy. The CUORE detector, currently being constructed underground at the Gran Sasso National Laboratory in Italy, is an array of 988 high-resolution TeO₂ bolometers. Each bolometer is comprised of a thermistor and a TeO₂ crystal that serves as both the source and the detector of 0&nu&beta&beta decay. The 0&nu&beta&beta decay signature for ¹³⁰Te is a peak at the Q-value 2528 keV. Observation of 0&nu&beta&beta decay requires that the background at the peak be ultra-low. Background-source identification and characterization are therefore extremely important.

One source of background that is poorly characterized is activation of the TeO₂ crystals by sea-level cosmic-ray neutrons. This process, known as cosmogenic activation, produces long-lived radioisotopes that can obscure the 0&nu&beta&beta peak. Existing cross-section data is insufficient to estimate this background; therefore, an additional cross-section measurement has been performed in which a TeO₂ target was irradiated with a neutron spectrum similar to that of cosmic-ray neutrons at sea-level. Analysis of the radionuclides produced reveals that ^110mAg will dominate the cosmogenic activation background in CUORE. Estimations using the measured cross section for ^110mAg indicate this source will be negligible compared with other contributions to the CUORE background.