Spins and magnetic moments of ⁴⁹K and ⁵¹K: Establishing the 1/2⁺ and 3/2⁺ level ordering beyond N = 28

J. Papuga, M. L. Bissell, K. Kreim, K. Blaum, B. A. Brown, M. De Rydt, R. F. Garcia Ruiz, H. Heylen, M. Kowalska, R. Neugart, G. Neyens, W. Nörtershäuser, T. Otsuka, M. M. Rajabali, R. Sánchez, Y. Utsuno, and D. T. Yordanov

Accepted Monday Mar 25, 2013

The ground-state spins and magnetic moments of 49,51K have been measured using bunched-beam high-resolution collinear laser spectroscopy at ISOLDE-CERN. For 49K a ground-state spin I = 1/2 was firmly established. The observed hyperfine structure of 51K requires a spin I > 1/2 and from its magnetic moment m(51\textK) = +0.5129(22) mN a spin/parity Ip=3/2+ with a dominant p1d3/2-1 hole configuration was deduced. This establishes for the first time the re-inversion of the single-particle levels and illustrates the prominent role of the residual monopole interaction for single-particle levels and shell evolution.