High-spin structures in the139Pr nucleus

Abstract

Background: ${}^{139}$Pr is located in a transitional region of neutron number close to the $N=82$ shell. The study of its high-spin states and collective bands is important for systematically understanding the nuclear structural characteristics in this region.Purpose: To investigate the high-spin levels and to search for oblate bands in ${}^{139}$Pr.Methods: The high-spin states of ${}^{139}$Pr have been studied via the reaction ${}^{124}$Sn(${}^{19}$F,4$n$) at a beam energy of 80 MeV. The experiment was carried out at the HI-13 Tandem Accelerator at the China Institute of Atomic Energy (CIAE). The data analysis was done by using the $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidence method.Results: The level scheme of ${}^{139}$Pr has been expanded with spin up to 45/2$\ensuremath{\hbar}$. A total of 39 new levels and 45 new transitions are identified. Four collective band structures at high-spin states have been newly established. From systematic analysis, one of the bands is proposed as a double decoupled band; two bands are proposed as oblate bands with $\ensuremath{\gamma}\ensuremath{\sim}\ensuremath{-}{60}^{\ensuremath{\circ}}$; another band is suggested as an oblate-triaxial band with $\ensuremath{\gamma}\ensuremath{\sim}\ensuremath{-}{90}^{\ensuremath{\circ}}$. The other characteristics for these bands are discussed.Conclusions: A new level scheme in ${}^{139}$Pr has been established and the collective bands at high spin have been identified. The result shows that the strong oblate shape-driving effect is caused by neutrons at the high-spin states in ${}^{139}$Pr.