Double-beta decay investigation with highly pure enriched (Formula presented.) Se for the LUCIFER experiment

The LUCIFER project aims at deploying the first array of enriched scintillating bolometers for the investigation of neutrinoless double-beta decay of (Formula presented.). The matrix which embeds the source is an array of ZnSe crystals, where enriched (Formula presented.) 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 (Formula presented.) 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 (Formula presented.) are respectively: (Formula presented.) at 90 % C.L. The extremely low-background conditions in which the measurement was carried out and the high radiopurity of the (Formula presented.) allowed us to establish the most stringent lower limits on the half-lives of the double-beta decay of (Formula presented.) excited states of (Formula presented.) y, respectively, with a 90 % C.L.