Band crossings in even-evenSm138andNd134

The rotational alignment of $h_{11/2}$ quasiparticles has been observed in the even-even ${}_{}{}^{138}{}_{}{}^{}\mathrm{Sm}$ and ${}_{}{}^{134}{}_{}{}^{}\mathrm{Nd}$ nuclei by means of heavy-ion fusion-evaporation reactions. The structures observed are compared to those found recently in ${}_{}{}^{136}{}_{}{}^{}\mathrm{Nd}$. The ground-state bands of the ${}_{}{}^{136}{}_{}{}^{}\mathrm{Nd}$ and ${}_{}{}^{138}{}_{}{}^{}\mathrm{Sm}$ isotones (N=76) possess significant triaxial shapes (γ∼-25°). Rotational alignment of $h_{11/2}$ protons induces a shape change towards the prolate (γ=0°) shape, while $h_{11/2}$ neutron alignment induces a change towards the oblate (γ=-60°) collective shape. In the more deformed ${}_{}{}^{134}{}_{}{}^{}\mathrm{Nd}$ nucleus, band crossings are observed in both the ground-state band and the γ-vibrational band. The crossing in the ground-state band is attributed to $h_{11/2}$ protons, while a second band that feeds into both the ground-state band and the γ-vibrational band is built on the [$h_{11/2}$ ${]}^2$ neutron-aligned configuration. In addition, negative-parity sidebands built on two-quasiproton configurations were seen in these nuclei. The systematics of the proton and neutron alignments are discussed.