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

TL;DR

This study measures the spins and magnetic moments of potassium isotopes $^{49}$K and $^{51}$K, revealing the re-inversion of single-particle levels and highlighting the importance of residual interactions in shell evolution.

Contribution

It provides the first experimental confirmation of the level re-inversion beyond N=28 in potassium isotopes, advancing understanding of shell structure.

Findings

$^{49}$K has a ground-state spin $I=1/2$.

$^{51}$K has a spin $I=3/2^+$ and a magnetic moment of +0.5129(22) μ_N.

Re-inversion of single-particle levels confirmed 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.