Gamma-ray spectra of neutron-deficient isotopes between cerium ($Z=58\mathrm{}$) and gadolinium ($Z=64\mathrm{}$) have been investigated. New bands of states were identified in many even-even, odd-$A$, and odd-odd nuclei. This Letter reports results on the ground-state bands in the even-even nuclei ${}_{58}{}^{126}{}_{}{}^{}\mathrm{Ce}_{68}^{}{}_{}{}^{}$, ${}_{60}{}^{128,130,132}{}_{}{}^{}\mathrm{Nd}_{68,70,72}^{}{}_{}{}^{}$, ${}_{62}{}^{134,136}{}_{}{}^{}\mathrm{Sm}_{72,74}^{}{}_{}{}^{}$, and ${}_{64}{}^{138,140}{}_{}{}^{}\mathrm{Gd}_{74,76}^{}{}_{}{}^{}$. The systematic trends of deformation are presented and compared with theoretical predictions. The lightest isotopes appear to be axially symmetric rotors with ${\epsilon }_2\gtrsim 0.3$.

• Received 20 May 1985

DOI:https://doi.org/10.1103/PhysRevLett.55.810