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

TL;DR

This study searches for electron capture decay in $^{176}$Lu using a novel LYSO scintillator detector setup, improving detection sensitivity and setting stricter limits on the decay's branching ratio.

Contribution

The paper introduces a combined LYSO scintillator and HP-Ge detector method with coincidence detection to enhance sensitivity in searching for $^{176}$Lu electron capture decay.

Findings

Improved upper limits on $^{176}$Lu EC decay branching ratios by factors of 3 to 30.

Demonstrated the effectiveness of coincidence detection with LYSO and HP-Ge detectors.

Provided more stringent constraints on the decay modes of $^{176}$Lu.

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.