Charge radii of neutron-deficient K36 and K37

D. M. Rossi, K. Minamisono, H. B. Asberry, G. Bollen, B. A. Brown, K. Cooper, B. Isherwood, P. F. Mantica, A. Miller, D. J. Morrissey, R. Ringle, J. A. Rodriguez, C. A. Ryder, A. Smith, R. Strum, and C. Sumithrarachchi
Phys. Rev. C 92, 014305 – Published 7 July 2015

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 N=28 shell closure is evident in the charge radii of the isotopic chains of K through Mn, a similar signature of the N=20 shell closure is absent in the Ca region.

Purpose: The isotope shift between neutron-deficient K36 and K37 was determined to investigate the change of the mean-square charge radii across N=20 in the K isotopic chain.

Methods: The D1 atomic hyperfine spectra of K36 and K37 were measured using an optical pumping and subsequent β-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 δν37,36=139(4)(3) MHz. Using a re-evaluated isotope shift, δν39,37=264(2)(3) MHz, the isotope shift relative to K39 was determined to be δν39,36=403(5)(4) MHz. The differential mean-square charge radius was then deduced as δr239,36=0.16(5)(8)fm2. The Skyrme energy-density functional and shell-model calculations overpredict the experimental values below N=20 and underpredict them above N=20, and their agreement is marginal.

Conclusions: The absence of the shell-closure signature at N=20 in the K isotopic chain is understood as a balance between the monopole and the quadrupole proton-core polarizations below and above N=20, respectively.

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  • Received 24 April 2015

DOI:https://doi.org/10.1103/PhysRevC.92.014305

©2015 American Physical Society

Authors & Affiliations

D. M. Rossi1,*, K. Minamisono1,2,†, H. B. Asberry1,3, G. Bollen1,2, B. A. Brown1,2, K. Cooper1,3, B. Isherwood1,2, P. F. Mantica1,3, A. Miller1,2, D. J. Morrissey1,3, R. Ringle1, J. A. Rodriguez1, C. A. Ryder1, A. Smith1, R. Strum1,2, and C. Sumithrarachchi1

  • 1National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA
  • 2Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA
  • 3Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA

  • *rossi@nscl.msu.edu
  • minamiso@nscl.msu.edu

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Vol. 92, Iss. 1 — July 2015

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