Radioactive Decay ofYb167

Abstract

Erbium oxide enriched to 35.1% in the mass number 164 was irradiated with 17- and 24-Mev alpha particles. An activity decaying by electron capture with a half-life of (17.7±0.2) minutes was produced and its assignment to ${\mathrm{Yb}}^{167}$ confirmed by the identification of the thulium $K$ x-ray and the well-known daughter activity of ${\mathrm{Tm}}^{167}$. Gamma rays with energies of 106, 113, and 176 kev were observed in the spectrum of ${\mathrm{Yb}}^{167}$. Gamma-gamma coincidence measurements were performed on the observed radiations. Transition probabilities, multipole order admixtures, and electron capture branching ratios have been calculated. Approximately 89% of the electron capture transitions occur to the 292.7-kev ($\frac{7}{2}-$) level of ${\mathrm{Tm}}^{167}$.