Abstract
Background: The systematic trend in mean-square charge radii as a function of proton or neutron number exhibits a discontinuity at the nucleon-shell closures. While the established shell closure is evident in the charge radii of the isotopic chains of K through Mn, a similar signature of the shell closure is absent in the Ca region.
Purpose: The isotope shift between neutron-deficient and was determined to investigate the change of the mean-square charge radii across in the K isotopic chain.
Methods: The atomic hyperfine spectra of and were measured using an optical pumping and subsequent -decay asymmetry detection technique. Atomic rate equations were solved to fit the resonant line shape. The result was compared to Skyrme energy-density functional and shell-model calculations.
Results: The isotope shift was obtained as MHz. Using a re-evaluated isotope shift, MHz, the isotope shift relative to was determined to be MHz. The differential mean-square charge radius was then deduced as . The Skyrme energy-density functional and shell-model calculations overpredict the experimental values below and underpredict them above , and their agreement is marginal.
Conclusions: The absence of the shell-closure signature at in the K isotopic chain is understood as a balance between the monopole and the quadrupole proton-core polarizations below and above , respectively.
- Received 24 April 2015
DOI:https://doi.org/10.1103/PhysRevC.92.014305
©2015 American Physical Society