Study of Low-Lying1−States inEr166,168,170Using the Resonant Scattering of Bremsstrahlung

In addition to the previously known $1^{-}$ states of ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}$ at 1663 and 1830 keV, levels at 1812 ± 1 keV (${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}$), 1786 ± 1 keV (${}_{}{}^{168}{}_{}{}^{}\mathrm{Er}$), and 1824 ± 1 keV (${}_{}{}^{170}{}_{}{}^{}\mathrm{Er}$) have been excited using electron bremsstrahlung. Based on the observed angular distributions of the scattered photons, all three previously unknown levels were found to have spin 1. Linear polarization measurements using a two-slab Ge(Li) polarimeter led to negative parity assignments for the 1786- and 1824-keV levels but were inconclusive with respect to the less strongly excited 1812-keV level. Below 1.9 MeV, the 1663-, 1786-, and 1824-keV levels are the dominant $E1\mathrm{}$ excitations in their respective isotopes, the partial widths of their ground-state transitions being ${\Gamma }_0=32\mathrm{}\pm 5,46\pm 5, \mathrm{and} 30\pm 3$ meV. The $\frac{B(E1;1^{-}\to \mathrm{g}.\mathrm{s}.\mathrm{})}{B(E1;1^{-}\to 2_1^{+})}$ ratios of 0.52 ± 0.02, 0.51 ± 0.02, and 0.53 ± 0.02 differ considerably from the ratio 1.31 ± 0.11 for the 1812-keV level and the reported ratio 0.22 for the 1830-keV $1^{-}$ state and are very close to the Alaga value of 0.50 for $K=0^{-}$ levels.