Spins and Magnetic Moments of 49K and 51K: Establishing the 1/2+ and 3/2+ Level Ordering Beyond N=28

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 strongly suggests I=3/2. From its magnetic moment mm(51K)=0,5129(22)mN a spin-parity I=3/2+ with a dominant 1d1 3=2 hole configuration was deduced. This establishes for the first time the reinversion of the single-particle levels and illustrates the prominent role of the residual monopole interaction for single-particle levels and shell evolution. 5 pages, 3 figures ispartof: Physical Review Letters vol:110 issue:17 ispartof: location:United States status: published