The LUCIFER project aims at deploying the first array of enriched scintillating bolometers for the investigation of neutrinoless double-beta decay of $^{ 82}$Se. The matrix which embeds the source is an array of ZnSe crystals, where enriched $^{ 82}$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 $^{ 82}$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 $^{ 232}$Th, $^{ 238}$U and $^{ 235}$U are respectively: $<$61 $\mu$Bq/kg, $< $110 $\mu$Bq/kg and $<$74 $\mu$Bq/kg at 90\% C.L.. The extremely low-background conditions in which the measurement was carried out and the high radiopurity of the $^{ 82}$Se allowed us to establish the most stringent lower limits on the half-lives of double-beta decay of $^{ 82}$Se to 0$^+_1$, 2$^+_2$ and 2$^+_1$ excited states of $^{ 82}$Kr of 3.4$\cdot$10$^{ 22}$ y, 1.3$\cdot$10$^{ 22}$ y and 1.0$\cdot$10$^{ 22}$ y, respectively, with a 90\% C.L..
Categories: physics.ins-det hep-ex nucl-ex