Hexadecapole strength in the rare isotopes ${}^{74,76}$Kr

Abstract

In the Ge-Sr mass region, isotopes with neutron number $N\le 40$ are known to feature rapid shape changes with both nucleon number and angular momentum. To gain new insights into their structure, inelastic proton scattering experiments in inverse kinematics were performed on the rare isotopes ${}^{74,76}$Kr. This work focuses on observables related to the $J^{\pi }=4_1^{+}$ states of the Kr isotopes and, in particular, on the hexadecapole degree of freedom. By performing coupled-channels calculations, hexadecapole deformation parameters ${\beta }_4$ were determined for the $J^{\pi }=4_1^{+}$ states of ${}^{74,76}$Kr from inelastic proton scattering cross sections. Two possible coupled-channels solutions were found. A comparison to predictions from nuclear energy density functional theory, employing both non-relativistic and relativistic functionals, clearly favors the large, positive ${\beta }_4$ solutions. These ${\beta }_4$ values are unambiguously linked to the well deformed prolate configuration. Given the ${\beta }_2-{\beta }_4$ trend, established in this work, it appears that ${\beta }_4$ values could provide a sensitive measure of the nuclear shell structure.

7 pages, 4 figures, accepted for publication in Physics Letters B

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• Quadrupole-hexadecapole coupling in the rare earth region with beyond mean field correlations
• Landscape of nuclear deformation softness with spherical quasi-particle random phase approximation
• Proton removal from ${}^{73,75}$Br to ${}^{72,74}$Se at intermediate energies
• Impacts of hexadecapole correlations in actinide nuclei