Shell structure of potassium isotopes deduced from their magnetic moments

Abstract

\item[Background] Ground-state spins and magnetic moments are sensitive to the nuclear wave function, thus they are powerful probes to study the nuclear structure of isotopes far from stability. \item[Purpose] Extend our knowledge about the evolution of the $1/2^{+}$ and $3/2^{+}$ states for K isotopes beyond the $N=28$ shell gap. \item[Method] High-resolution collinear laser spectroscopy on bunched atomic beams. \item[Results] From measured hyperfine structure spectra of K isotopes, nuclear spins and magnetic moments of the ground states were obtained for isotopes from $N=19$ up to $N=32$. In order to draw conclusions about the composition of the wave functions and the occupation of the levels, the experimental data were compared to shell-model calculations using SDPF-NR and SDPF-U effective interactions. In addition, a detailed discussion about the evolution of the gap between proton $1d_{3/2}$ and $2s_{1/2}$ in the shell model and {\it{ab initio}} framework is also presented. \item[Conclusions] The dominant component of the wave function for the odd-$A$ isotopes up to ${}^{45}$K is a $\pi 1d_{3/2}^{-1}$ hole. For ${}^{47,49}$K, the main component originates from a $\pi 2s_{1/2}^{-1}$ hole configuration and it inverts back to the $\pi 1d_{3/2}^{-1}$ in ${}^{51}$K. For all even-$A$ isotopes, the dominant configuration arises from a $\pi 1d_{3/2}^{-1}$ hole coupled to a neutron in the $\nu 1f_{7/2}$ or $\nu 2p_{3/2}$ orbitals. Only for ${}^{48}$K, a significant amount of mixing with $\pi 2s_{1/2}^{-1}\otimes \nu (pf)$ is observed leading to a $I^{\pi }=1^{-}$ ground state. For ${}^{50}$K, the ground-state spin-parity is $0^{-}$ with leading configuration $\pi 1d_{3/2}^{-1}\otimes \nu 2p_{3/2}^{-1}$.

Comments: 12 pages, 10 figures, 7 tables