Radioactive Decay of Lutetium-174

Ytterbium oxide enriched to 98.4% in the 174 mass number was irradiated with 6-Mev protons. An activity of approximately 165-day half-life was produced and assigned to ${\mathrm{Lu}}^{174}$ by the identification of the ytterbium $K$ x-ray and of the activities produced by similar proton irradiations of the other enriched isotopes of ytterbium. The observed activity of ${\mathrm{Lu}}^{174}$ consists of the $L$ and $K$ x-rays of ytterbium and 76.6- and 1228-kev gamma rays which are in coincidence. Because no beta radiation exists in the activity of ${\mathrm{Lu}}^{174}$, the mode of decay is solely by electron capture to ${\mathrm{Yb}}^{174}$. Approximately 31% of the disintegrations of ${\mathrm{Lu}}^{174}$ are to the ground state of ${\mathrm{Yb}}^{174}$. In addition to the 76.6-kev level of ${\mathrm{Yb}}^{174}$, there is a 1305-kev level with a spin of 0+. The transitions of ${\mathrm{Lu}}^{174}$ to the 1305-kev level of ${\mathrm{Yb}}^{174}$ are by $L$ capture only and the percentages of electron capture to the 76.6- and 1305-kev levels of ${\mathrm{Yb}}^{174}$ are approximately 59 and 10, respectively. A spin of 1- is assigned to the ground state of ${\mathrm{Lu}}^{174}$.