High spin structure in the odd-proton nucleusPr133

The odd-proton nucleus ${}_{}{}^{133}{}_{}{}^{}\mathrm{Pr}$ has been investigated using the ${}_{}{}^{118}{}_{}{}^{}\mathrm{F}$,4n) and ${}_{}{}^{117}{}_{}{}^{}\mathrm{F}$,3n) reactions. Several rotational bands could be followed up to high spins. The yrast band, built on a decoupled $h_{11/2}$ proton, shows an upbend at ħω=0.43 MeV when two additional $h_{11/2}$ protons align. Two positive-parity side bands of opposite signature were established, both showing a band crossing at ħω=0.27 MeV with a gain in alignment Δ$i_x$∼8ħ when two $h_{11/2}$ protons align. This low crossing frequency, compared to that observed in the ${}_{}{}^{132}{}_{}{}^{}\mathrm{Ce}$ core nucleus, is partly explained by a reduction in the proton pairing gap. Three ΔI=1 bands were observed; the lowest one is believed to represent a collective rotation of an oblate shape. The shape change is induced by the alignment of a pair of $h_{11/2}$ neutrons from the upper midshell driving the nucleus from a prolate to an oblate shape.