Double-beta decay investigation with highly pure enriched $$^82$$ 82 Se for the LUCIFER experiment

The LUCIFER project aims at deploying the first array of enriched scintillating bolometers for the investiga- tion of neutrinoless double-beta decay of 82Se. The matrix which embeds the source is an array of ZnSe crystals, where enriched 82Se is used as decay isotope. The radiopurity of the initial components employed for manufacturing crystals, that can be operated as bolometers, is crucial for achieving a null background level in the region of interest for double- beta decay investigations. In this work, we evaluated the radioactive content in 2.5 kg of 96.3 % enriched 82Se metal, measured with a high-purity germanium detector at the Gran Sasso deep underground laboratory. The limits on internal contaminations of primordial decay chain elements of 232Th, 238 U and 235 U are respectively: <61, <110 and <74 μBq/kg at 90 % C.L. The extremely low-background conditions in which the measurement was carried out and the high radiop- urity of the 82Se allowed us to establish the most stringent lower limits on the half-lives of the double-beta decay of 82 Se to 0+1 , 2+2 and 2+1 excited states of 82 Kr of 3.4·1022 , 1.3·1022 and 1.0·1022 y, respectively, with a 90 % C.L.