Radioactive Decay ofLu170

Ytterbium oxide enriched to 81.4% in the 170 mass number was irradiated with 6-Mev protons. An activity decaying by electron capture with a half-life of (2.05±0.05) days was produced and assigned to ${\mathrm{Lu}}^{170}$ by the identification of the ytterbium $K$ x ray and by comparison with the activities produced by similar proton irradiations of each of the other enriched isotopes of ytterbium. The observed activity consists of the ytterbium $K$ x ray, gamma rays with energies of 84, 193, 245, 1010, 1030, 1165, 1275, 1415, 2035, 2365, 2665, 2890, and 3085 kev, and a small amount of annihilation radiation. Because no particle radiation exists, the mode of decay of ${\mathrm{Lu}}^{170}$ is solely by electron capture to ${\mathrm{Yb}}^{170}$. Gamma-gamma coincidence measurements have led to the postulation of levels in ${\mathrm{Yb}}^{170}$ at 2120 (0), 2365 (1 or 2), 3170 (3), and 3395 (1 or 2) kev in addition to the previously assigned 84 (2+), and 278 (4+) levels. A partial energy level scheme with approximate electron capture branching ratios is proposed.