Early signal of emerging nuclear collectivity in neutron-rich ${}^{129}$Sb

Abstract

Radioactive ${}^{129}$Sb, which can be treated as a proton plus semi-magic ${}^{128}$Sn core within the particle-core coupling scheme, was studied by Coulomb excitation. Reduced electric quadrupole transition probabilities, $B(E2)$, for the $2^{+}$ $\times$ $\pi g_{7/2}$ multiplet members and candidate $\pi d_{5/2}$ state were measured. The results indicate that the total electric quadrupole strength of ${}^{129}$Sb is a factor of 1.39(11) larger than the ${}^{128}$Sn core, which is in stark contrast to the expectations of the empirically successful particle-core coupling scheme. Shell-model calculations performed with two different sets of nucleon-nucleon interactions suggest that this enhanced collectivity is due to constructive quadrupole coherence in the wavefunctions stemming from the proton-neutron residual interactions, where adding one nucleon to a core near a double-shell closure can have a pronounced effect. The enhanced electric quadrupole strength is an early signal of the emerging nuclear collectivity that becomes dominant away from the shell closure.

Accepted, Physical Review Letters

References in corpus (2)

• Emerging collectivity from the nuclear structure of ${}^{132}$Xe: Inelastic neutron scattering studies and shell-model calculations
• Effective field theory for vibrations in odd-mass nuclei