Electron Capture Decay ofTm168andTm166

The electron capture of ${\mathrm{Tm}}^{168}$ (87 day) to levels in ${\mathrm{Er}}^{168}$ was investigated with permanent magnet spectrographs and coincidence scintillation spectrometers. The following levels in ${\mathrm{Er}}^{168}$ have been established: 79.8(2+), 264.3(4+), 548.9(6+), 822.4(2+), 897.0(3+), 996.2(4+), 1095.1(3- and $T_{\frac{1}{2}}=1.2\mathrm{}\times {10}^{-7\mathrm{}}$ sec), and 1543.1(3)-) kev. The internal conversion data for ${\mathrm{Tm}}^{166}$ (7.7 hour) suggest levels in ${\mathrm{Er}}^{166}$ at 80.6(2+), 265.1(4+), 545.3(6+), 787.1(2+), 860.6(3+), and 957.2(4+) kev. with many more high lying levels. Energy level schemes are proposed for both ${\mathrm{Er}}^{168}$ and ${\mathrm{Er}}^{166}$. The levels at 822, 897, and 996 kev in ${\mathrm{Er}}^{168}$ and 787, 861, and 957 kev in ${\mathrm{Er}}^{166}$ may possibly be associated with electric quadrupole (gamma) vibrations. Some general features regarding these vibrational levels are discussed and compared with available data on other even-even nuclei in the rare earth region.