Nuclear resonance fluorescence inSm144

Using electron bremsstrahlung with up to 5.2-MeV end-point energy, the resonant scattering of $\gamma$ rays by an enriched sample of ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ has been studied. Ground-state transitions were observed from a dozen levels, and the scattering yields, measured at 96° and 126°, were evaluated in terms of radiative widths and level spins. For the strongest excitations, these measurements were supplemented by self-absorption and linear-polarization studies. Some of the observed $E1\mathrm{}$ transitions originate from $1^{-}$ states which, according to isobaric-analog-resonance studies, contain large neutron-particle-hole components. On the other hand, the 3.225- and 3.891-MeV levels, which exhibit the strongest $E1\mathrm{}$ ground-state transitions, occur at energies which suggest that they arise from the coupling of the lowest octupole vibration to the $2_1^{+}$ and $2_2^{+}$ levels.