Charge radii of exotic potassium isotopes challenge nuclear theory and the magic character of N = 32

• Main Authors: Koszorús, Á (Author), Yang, XF (Author), Jiang, WG (Author), Novario, SJ (Author), Bai, SW (Author), Billowes, J (Author), Binnersley, CL (Author), Bissell, ML (Author), Cocolios, TE (Author), Cooper, BS (Author), de Groote, RP (Author), Ekström, A (Author), Flanagan, KT (Author), Forssén, C (Author), Franchoo, S (Author), Ruiz, RF Garcia (Author), Gustafsson, FP (Author), Hagen, G (Author), Jansen, GR (Author), Kanellakopoulos, A (Author), Kortelainen, M (Author), Nazarewicz, W (Author), Neyens, G (Author), Papenbrock, T (Author), Reinhard, P-G (Author), Ricketts, CM (Author), Sahoo, BK (Author), Vernon, AR (Author), Wilkins, SG (Author)
• Format: Article
• Language: English
• Published: Springer Science and Business Media LLC, 2022-04-13T15:24:29Z.
• Subjects: Article
• Online Access: Get fulltext

© 2020, The Author(s), under exclusive licence to Springer Nature Limited. Nuclear charge radii are sensitive probes of different aspects of the nucleon-nucleon interaction and the bulk properties of nuclear matter, providing a stringent test and challenge for nuclear theory. Experimental evidence suggested a new magic neutron number at N = 32 (refs. 1-3) in the calcium region, whereas the unexpectedly large increases in the charge radii4,5 open new questions about the evolution of nuclear size in neutron-rich systems. By combining the collinear resonance ionization spectroscopy method with β-decay detection, we were able to extend charge radii measurements of potassium isotopes beyond N = 32. Here we provide a charge radius measurement of 52K. It does not show a signature of magic behaviour at N = 32 in potassium. The results are interpreted with two state-of-the-art nuclear theories. The coupled cluster theory reproduces the odd-even variations in charge radii but not the notable increase beyond N = 28. This rise is well captured by Fayans nuclear density functional theory, which, however, overestimates the odd-even staggering effect in charge radii. These findings highlight our limited understanding of the nuclear size of neutron-rich systems, and expose problems that are present in some of the best current models of nuclear theory.