Spins and Magnetic Moments of ${}^{49}$K and ${}^{51}$K: establishing the 1/2${}^{+}$ and 3/2${}^{+}$ level ordering beyond $N$ = 28

Abstract

The ground-state spins and magnetic moments of ${}^{49,51}$K have been measured using bunched-beam high-resolution collinear laser spectroscopy at ISOLDE-CERN. For ${}^{49}$K a ground-state spin $I=1/2$ was firmly established. The observed hyperfine structure of ${}^{51}$K requires a spin $I>1/2$ and from its magnetic moment $\mu {(}^{51}\text{K})=+0.5129(22){\mu }_N$ a spin/parity $I^{\pi }=3/2^{+}$ with a dominant $\pi 1d_{3/2}^{-1}$ 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.

Comments: 5 pages, 3 figures