Radioactive Decay ofTm164andTm162

Erbium oxide enriched to 35.1% and 14.1% in the mass numbers 164 and 162, respectively, were irradiated with 6-Mev protons. Activities decaying by electron capture with half-lives of (2.04±0.10) minutes and (77±4) minutes were produced and are assigned to ${\mathrm{Tm}}^{164}$ and ${\mathrm{Tm}}^{162}$, respectively, by the identification of the erbium $K$ x ray, comparison with the activities produced by similar proton irradiations of each of the other enriched isotopes of erbium, and by the existence in the 2.04-minute activity of a prominent gamma ray with the energy of the first excited level in ${\mathrm{Er}}^{164}$ determined from the decay of ${\mathrm{Ho}}^{164}$. The gamma-ray spectrum of ${\mathrm{Tm}}^{164}$ consists of only the erbium $K$ x ray, a gamma ray of 91 kev, and annihilation radiation; and that of ${\mathrm{Tm}}^{162}$, of the erbium $K$ x ray and gamma rays of 102 and 236 kev. The three radiations observed in the decay of ${\mathrm{Tm}}^{162}$ are all in coincidence. Energy level schemes for the decay of these two new activities are proposed and branching ratios are estimated from relative intensities.