Seven-quasiparticle bands inCe139

Abstract

The high spin states in the $^{139}\mathrm{Ce}$ nucleus have been studied by in-beam $\ensuremath{\gamma}$-spectroscopic techniques using the reaction $^{130}\mathrm{Te}(^{12}\mathrm{C},3n)^{139}\mathrm{Ce}$ at ${E}_{\mathrm{beam}}=65$ MeV. A gamma detector array, consisting of five Compton-suppressed Clover detectors was used for coincidence measurements. 15 new levels have been proposed and 28 new $\ensuremath{\gamma}$ transitions have been assigned to $^{139}\mathrm{Ce}$ on the basis of $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence data. The level scheme of $^{139}\mathrm{Ce}$ has been extended above the known 70 ns ${\frac{19}{2}}^{\ensuremath{-}}$ isomer up to $~6.1$ MeV in excitation energy and $\frac{35}{2}\ensuremath{\hbar}$ in spin. The spin-parity assignments for most of the newly proposed levels have been made using the deduced Directional Correlation from Oriented states of nuclei (DCO ratio) and the Polarization Directional Correlation from Oriented states (PDCO ratio) for the de-exciting transitions. The observed level structure has been compared with a large basis shell model calculation and also with the predictions from cranked Nilsson-Strutinsky (CNS) calculations. A general consistency has been observed between these two different theoretical approaches.