High spin states in ${}_{}{}^{129}{}_{}{}^{}\mathrm{Pr}$ and ${}_{}{}^{131}{}_{}{}^{}\mathrm{Pr}$ have been investigated using in-beam γ-ray spectroscopy techniques. The yrast band of ${}_{}{}^{129}{}_{}{}^{}\mathrm{Pr}$ based on the ${\mathit{h}}_{11/2}$ 3/$2^{\mathrm{-}}$[541] proton configuration was observed from 11/$2^{\mathrm{-}}$ up to 43/$2^{\mathrm{-}}$. The band based on the same configuration and two positive-parity side bands based on the ${\mathit{g}}_{7/2}$ 5/$2^{+}$[413] proton configuration, were observed in ${}_{}{}^{131}{}_{}{}^{}\mathrm{Pr}$. The delayed yrast band crossing of ${}_{}{}^{129}{}_{}{}^{}\mathrm{Pr}$ at ħ${\mathrm{\omega }}_{\mathit{c}}$=0.37 MeV is interpreted as being due to the alignment of the second and third ${\mathit{h}}_{11/2}^{\mathrm{-}}$ protons. The band crossing at ħ${\mathrm{\omega }}_{\mathit{c}}$=0.26 MeV, with a gain in alignment of about 8ħ, based on the ${\mathit{g}}_{7/2}$ 5/$2^{+}$[413] configuration in ${}_{}{}^{131}{}_{}{}^{}\mathrm{Pr}$ was attributed to the alignment of two ${\mathit{h}}_{11/2}$ protons. The systematics of the proton alignments in a series of Pr isotopes is discussed.

• Received 17 September 1991

DOI:https://doi.org/10.1103/PhysRevC.47.1428