Using the techniques of in-beam $\gamma$-ray spectroscopy, the high-spin states in the odd-mass ${}_{}{}^{119-125}{}_{}{}^{}\mathrm{Cs}$ have been studied via the ${}_{}{}^{106}{}_{}{}^{}\mathrm{Cd}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,$p2n$)${}_{}{}^{119}{}_{}{}^{}\mathrm{Cs}$, ${}_{}{}^{110-114}{}_{}{}^{}\mathrm{Cd}$(${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$,$3n$)${}_{}{}^{121-125}{}_{}{}^{}\mathrm{Cs}$, and ${}_{}{}^{116,118}{}_{}{}^{}\mathrm{Sn}$(${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$,$3n$)${}_{}{}^{123,125}{}_{}{}^{}\mathrm{Cs}$ reactions on enriched, self-supporting targets. Two distinct collective features are observed in the resulting level schemes: $\Delta J=2\mathrm{}$ bands built on the $\frac{11}{2^{-}}$ ($1h_{\frac{11}{2}}$ quasi-proton states, and $\Delta J=1\mathrm{}$ bands built on the $\frac{9}{2^{+}}$ ($1g_{\frac{9}{2}}$ proton-hole) states. The $\frac{9}{2^{+}}$ bandheads, believed to result from the excitation of the $1g_{\frac{9}{2}}$ proton across the $Z=50\mathrm{}$ closed shell, are observed at surprisingly low energies, becoming the ground state in ${}_{}{}^{119}{}_{}{}^{}\mathrm{Cs}$. The systematics of the $\frac{9}{2^{+}}$ $\Delta J=1\mathrm{}$ bands are presented and discussed in terms of the particle-plus-rotor and particle-plus-vibrator models. A deformed structure relationship between the excitation of a $1g_{\frac{9}{2}}$ proton and the excitation of a pair of $1g_{\frac{9}{2}}$ protons across the $Z=50\mathrm{}$ closed shell is discussed.

NUCLEAR REACTIONS ${}_{}{}^{106}{}_{}{}^{}\mathrm{Cd}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,$p2n$)${}_{}{}^{119}{}_{}{}^{}\mathrm{Cs}$, ${}_{}{}^{110-114}{}_{}{}^{}\mathrm{Cd}$(${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$,$3n$)${}_{}{}^{121-125}{}_{}{}^{}\mathrm{Cs}$, ${}_{}{}^{116,118}{}_{}{}^{}\mathrm{Sn}$ (${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$,$3n$)${}_{}{}^{123,125}{}_{}{}^{}\mathrm{Cs}$; measured $\gamma -\gamma$ coincidence, $\gamma (E,\theta )$; deduced level schemes in odd-mass ${}_{}{}^{119-125}{}_{}{}^{}\mathrm{Cs}$, $\gamma$ multipolarities, $J^{\pi }$. Enriched targets, Ge (Li) detectors. NUCLEAR STRUCTURE Odd-mass ${}_{}{}^{119-125}{}_{}{}^{}\mathrm{Cs}$, calculated ${\frac{9}{2}}^{+}$ $\Delta J=1\mathrm{}$ rotational bands.

• Received 2 August 1978

DOI:https://doi.org/10.1103/PhysRevC.19.217