Radiations from the Active Isotopes of Ytterbium

By using Yb of high purity (99.8%) irradiated in the maximum flux of the Argonne pile and studied by scintillation and magnetic photographic spectrometers, a reevaluation of the energies of the radiations has been made. Several previously unreported gamma rays are found and nuclear level schemes for ${\mathrm{Tm}}^{169}$, ${\mathrm{Lu}}^{175}$, and ${\mathrm{Lu}}^{177}$ are proposed. Several of the levels appear to be rotational states in the unified nuclear model. ${\mathrm{Yb}}^{169}$ decays with a half-life of 30.6 days by $K$ capture, followed by eleven gamma rays in ${\mathrm{Tm}}^{169}$. Rotational levels lie at 8.4, 118.3, and 139.1 kev. The gamma energies are 8.4, 20.6, 63.2, 93.6, 109.9, 118.3, 130.7, 177.7, 198.6, 261.0, and 308.3 kev. ${\mathrm{Yb}}^{175}$ decays with a half-life of 4.2 days by $\beta$ emission (471 kev max) followed by five gamma rays in ${\mathrm{Lu}}^{175}$. Rotational levels exist at 114.1, and 251.9 kev. The gamma energies are 114.1, 137.8, 145.0, 282.9, and 397.0 kev. ${\mathrm{Yb}}^{177}$ decays with a half-life of 1.88 hour by $\beta$ emission followed by gamma transitions in ${\mathrm{Lu}}^{177}$. In addition to any lower energy gamma rays, two high-energy transitions are found at 1.080 and 1.228 Mev. The latter is a cross over for the 1.080- and 0.148-Mev gammas which are in coincidence. The expected well-known daughter product ${\mathrm{Lu}}^{177}$, if present at all, is too weak to be observed by the magnetic spectrometers.