Performances of a SrI₂(Eu) crystal scintillator and its application to the search of ⁸⁴Sr β β decay

A new strontium iodide crystal doped by europium (SrI ₂ 2 (Eu); mass \, \, ≃ 130 g) was produced by selected materials using the vertical Bridgman method. It was measured over 4140 h deep underground at the Gran Sasso National Laboratory (LNGS) of the INFN in the DAMA/CRYS low-background set-up. A characterization of the crystal features and performances has preliminarily been investigated. The obtained results have been used in the search for the double electron capture and electron capture with positron emission in ⁸⁴ 84 Sr; new and improved limits have been achieved for these processes, with half-lives T1/2 T 1 / 2 reaching the level of several 10 ¹⁷ 17 yr. Further improvements of low background techniques in the SrI ₂ 2 (Eu) crystal development would offer additional increase of reachable experimental sensitivities on ⁸⁴ 84 Sr β β β β decay modes.