Measurement of 190Pt alpha decay modes with gamma emission using a novel approach with an ultra-low-background high purity germanium detector

Abstract

A new measurement of 190Pt alpha decay modes to the first and second excited level of 186Os has been done at the Gran Sasso Underground Laboratory (LNGS, Italy). With a new experimental set-up a total exposure of 23.107 kg d has been accumulated. The novel approach to detect rare decays made it possible to measure the half-life for the alpha decay into the first excited state of 190Pt with the highest precision to date as T1/2 = 2.59 ± 0.04 (stat.) ± 0.24 (syst.) × 1014 a, in which systematic uncertainties dominate. The search for the alpha decay into the second excited state of 186Os resulted in a lower limit of 2.8 × 1016 a (90% C.L.), which is nonetheless an improvement of one order of magnitude compared to existing results.