Search for alpha decay of naturally occurring osmium nuclides accompanied by gamma quanta

TL;DR

This study conducted a sensitive search for alpha decay in natural osmium isotopes using a low-background gamma detector, setting new lower limits on decay half-lives that surpass theoretical predictions.

Contribution

It provides the first experimental lower limits on alpha decay half-lives of osmium isotopes, improving upon previous estimates and utilizing high-precision isotopic measurements.

Findings

No alpha decay signals detected after 15851 hours.

Lower limits on half-lives range from 10^{15} to 10^{19} years.

Limits for $^{184}$Os and $^{186}$Os exceed theoretical estimates.

Abstract

A search for $\alpha$ decay of naturally occurring osmium isotopes to the lowest excited levels of daughter nuclei has been performed by using an ultra-low-background Broad-Energy Germanium $\gamma$-detector with a volume of 112 cm$^3$ and an ultra-pure osmium sample with a mass of 118 g at the Gran Sasso National Laboratory of the INFN (Italy). The isotopic composition of the osmium sample has been measured with high precision using Negative Thermal Ionisation Mass Spectrometry. After 15851 h of data taking with the $\gamma$-detector no effect has been detected, and lower limits on the $\alpha$ decays were set at level of $\lim T_{1/2}\sim 10^{15}-10^{19}$ yr. The limits for the $\alpha$ decays of $^{184}$Os and $^{186}$Os to the first excited levels of daughter nuclei, $T_{1/2}(^{184}$Os$)\geq 6.8\times10^{15}$ yr and $T_{1/2}(^{186}$Os$)\geq3.3\times10^{17}$ yr (at 90% C.L.), exceed the present theoretical estimates of the decays half-lives. For $^{189}$Os and $^{192}$Os also decays to the ground states of the daughter nuclei were searched for due to the instability of the daughter nuclides relative to $\beta$ decay.