Search for $\alpha$ decay of $^{151}$Eu to the first excited level of $^{147}$Pm using underground $\gamma$-ray spectrometry

TL;DR

This study conducted an underground gamma-ray spectrometry experiment to search for alpha decay of europium isotopes, setting new lower limits on their half-lives and discussing potential improvements to increase sensitivity.

Contribution

The paper reports the first search for alpha decay of $^{151}$Eu to the first excited state of $^{147}$Pm and establishes improved half-life limits, approaching theoretical predictions.

Findings

New half-life limit for $^{151}$Eu decay: ≥ 3.7×10^{18} years

New half-life limit for $^{153}$Eu decay: ≥ 5.5×10^{17} years

Experiment sensitivity close to theoretical decay predictions

Abstract

The alpha decay of $^{151}$Eu to the first excited level of $^{147}$Pm ($J^\pi = 5/2^+$, $E_{exc}=91.1$ keV) was searched for at the HADES underground laboratory ($\approx 500$ m w.e.). A sample of high purity europium oxide with mass of 303 g and a natural isotopic composition has been measured over 2232.8 h with a high energy resolution ultra-low background n-type semi-planar HPGe detector (40 cm$^3$) with sub-micron deadlayer. The new improved half-life limit has been set as $T_{1/2} \geq 3.7\times 10^{18}$ yr at 68% C.L. Possibilities to improve the sensitivity of the experiment, which is already near the theoretical predictions, are discussed. New half-life limit for $\alpha$ decay of $^{153}$Eu is also set as $T_{1/2} \geq 5.5\times 10^{17}$ yr.