First search for $\alpha$ decays of naturally occurring Hf nuclides with emission of $\gamma$ quanta

TL;DR

This study conducted the first search for alpha decays of naturally occurring hafnium isotopes to excited states in ytterbium, setting new lower bounds on their half-lives using ultra low-background gamma spectroscopy.

Contribution

It is the first experimental search for alpha decays of Hf isotopes to excited states, providing new lower bounds on their half-lives.

Findings

No decays detected within measurement sensitivity.

Lower bounds on half-lives range from 10^{15} to 10^{18} years.

Established the decay half-life limit for $^{174}$Hf to the 2+ excited state.

Abstract

The first ever search for $\alpha$ decays to the first excited state in Yb was performed for six isotopes of hafnium (174, 176, 177, 178, 179, 180) using a high purity Hf-sample of natural isotopic abundance with a mass of 179.8 g. For $^{179}$Hf, also $\alpha$ decay to the ground state of $^{175}$Yb was searched for thanks to the $\beta$-instability of the daughter nuclide $^{175}$Yb. The measurements were conducted using an ultra low-background HPGe-detector system located 225 m underground. After 75 d of data taking no decays were detected but lower bounds for the half-lives of the decays were derived on the level of $\lim T_{1/2}\sim 10^{15}-10^{18}$~a. The decay with the shortest half-life based on theoretical calculation is the decay of $^{174}$Hf to the first $2^+$ 84.3~keV excited level of $^{170}$Yb. The experimental lower bound was found to be $T_{1/2}\geq 3.3\times 10^{15}$ a.