Excited states have been studied in ${}^{159}\mathrm{Sm}, {}^{161}\mathrm{Sm}, {}^{162}\mathrm{Sm}$ ($Z=62$), ${}^{163}\mathrm{Eu}$ ($Z=63$), and ${}^{164}\mathrm{Gd}$ ($Z=64$), populated by isomeric decay following ${}^{238}\mathrm{U}$ projectile fission at RIBF, RIKEN. The isomer half-lives range from 50 ns to $2.6\mu \mathrm{s}$. In comparison with other published data, revised interpretations are proposed for ${}^{159}\mathrm{Sm}$ and ${}^{163}\mathrm{Eu}$. The first data for excited states in ${}^{161}\mathrm{Sm}$ are presented, where a 2.6-$\mu \mathrm{s}$ isomer is assigned a three-quasiparticle, $K^{\pi }=17/2^{-}$ structure. The interpretation is supported by multi-quasiparticle Nilsson-BCS calculations, including the blocking of pairing correlations. A consistent set of reduced $E1$ hindrance factors is obtained. Limited evidence is also reported for isomeric decay in ${}^{163}\mathrm{Sm}, {}^{164}\mathrm{Eu}$, and ${}^{165}\mathrm{Eu}$.

• Received 4 July 2017
• Revised 9 August 2017

DOI:https://doi.org/10.1103/PhysRevC.96.034305