학술논문
Charge radii of exotic potassium isotopes challenge nuclear theory and the magic character of $N = 32$
Document Type
Working Paper
Author
Koszorús, Á.; Yang, X. F.; Jiang, W. G.; Novario, S. J.; Bai, S. W.; Billowes, J.; Binnersley, C. L.; Bissell, M. L.; Cocolios, T. E.; Cooper, B. S.; de Groote, R. P.; Ekström, A.; Flanagan, K. T.; Forssén, C.; Franchoo, S.; Ruiz, R. F. Garcia; Gustafsson, F. P.; Hagen, G.; Jansen, G. R.; Kanellakopoulos, A.; Kortelainen, M.; Nazarewicz, W.; Neyens, G.; Papenbrock, T.; Reinhard, P. -G.; Sahoo, B. K.; Ricketts, C. M.; Vernon, A. R.; Wilkins, S. G.
Source
Nature Physics 17, 439 (2021)
Subject
Language
Abstract
Nuclear charge radii are sensitive probes of different aspects of the nucleon-nucleon interaction and the bulk properties of nuclear matter; thus, they provide a stringent test and challenge for nuclear theory. The calcium region has been of particular interest, as experimental evidence has suggested a new magic number at $N = 32$ [1-3], while the unexpectedly large increases in the charge radii [4,5] open new questions about the evolution of nuclear size in neutron-rich systems. By combining the collinear resonance ionization spectroscopy method with $\beta$-decay detection, we were able to extend the charge radii measurement of potassium ($Z =19$) isotopes up to the exotic $^{52}$K ($t_{1/2}$ = 110 ms), produced in minute quantities. Our work provides the first charge radii measurement beyond $N = 32$ in the region, revealing no signature of the magic character at this neutron number. The results are interpreted with two state-of-the-art nuclear theories. For the first time, a long sequence of isotopes could be calculated with coupled-cluster calculations based on newly developed nuclear interactions. The strong increase in the charge radii beyond $N = 28$ is not well captured by these calculations, but is well reproduced by Fayans nuclear density functional theory, which, however, overestimates the odd-even staggering effect. These findings highlight our limited understanding on the nuclear size of neutron-rich systems, and expose pressing problems that are present in some of the best current models of nuclear theory.
Comment: submitted version; revision accepted in Nature Physics
Comment: submitted version; revision accepted in Nature Physics