First search for $\hat{I}\pm$ decays of naturally occurring Hf nuclides with emission of ${\hat{I}}^3$ quanta

Abstract

The first ever search for $\hat{I}\pm$ 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 $\hat{I}\pm$ decay to the ground state of ${}^{175}$Yb was searched for thanks to the ${\hat{I}}^2$-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 $T_{1/2}\ge 3.3\times 10^{15}$ a.

19 pages, 7 figures, 7 tables