Lawrence Berkeley National Laboratory

The LUCIFER project aims at deploying the first array of enriched scintillating bolometers for the investigation of neutrinoless double-beta decay of 82$$^{82}$$Se. The matrix which embeds the source is an array of ZnSe crystals, where enriched 82$$^{82}$$Se 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 82$$^{82}$$Se 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 232$$^{232}$$Th, 238$$^{238}$$U and 235$$^{235}$$U are respectively: <$$<$$61, <$$<$$110 and <$$<$$74 μ$$\mu $$Bq/kg at 90 % C.L. The extremely low-background conditions in which the measurement was carried out and the high radiopurity of the 82$$^{82}$$Se allowed us to establish the most stringent lower limits on the half-lives of the double-beta decay of 82$$^{82}$$Se to 01+$$^+_1$$, 22+$$^+_2$$ and 21+$$^+_1$$ excited states of 82$$^{82}$$Kr of 3.4·$$\cdot $$1022$$^{22}$$, 1.3·$$\cdot $$1022$$^{22}$$ and 1.0·$$\cdot $$1022$$^{22}$$ y, respectively, with a 90 % C.L.