Search for Electron Capture in ${}^{176}$Lu with LYSO scintillator

Abstract

The nuclide ${}^{176}$Lu is one of the few naturally occurring isotopes that are potentially unstable with respect to electron capture (EC). Although experimental evidence for ${}^{176}$Lu EC decay is still missing, this isotope is instead well known to ${\beta }^{-}$ decay into ${}^{176}$Hf with an half-life of about 38 Gyr. The precise investigation of all ${}^{176}$Lu possible decay modes is interesting because the Lu/Hf ratio is adopted as an isotopic clock. Previous searches for the ${}^{176}$Lu EC decay were performed by using a passive Lutetium source coupled with an HP-Ge spectrometer. Our approach uses a LYSO crystal both as Lutetium source and as an active detector. Scintillation light from the LYSO crystal is acquired in coincidence with the signals from the HP-Ge detector, this allows a powerful suppression of the background sourcing from the well known ${\beta }^{-}$ decay branch. This coincidence approach led to an improvement on the ${}^{176}$Lu EC branching ratio limits by a factor 3 to 30, depending on the considered EC channel.

9 pages, 14 figures

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