Doubly-magic nature of 56Ni: measurement of the ground state nuclear magnetic dipole moment of 55Ni

TL;DR

This study measures the nuclear magnetic moment of 55Ni, compares it with shell model calculations, and discusses implications for the nuclear structure and core softness of 56Ni.

Contribution

First measurement of the magnetic moment of 55Ni's ground state, supporting shell model predictions and insights into nuclear core properties.

Findings

Measured magnetic moment of 55Ni: 0.976 ± 0.026 μ_N

Shell model calculations reproduce experimental value

Supports the softness of the 56Ni core

Abstract

The nuclear magnetic moment of the ground state of $^{55}$Ni ($I^{\pi}=3/2^{-}, T_{1/2}=204$ ms) has been deduced to be $|\mu$^{55}Ni)$|=(0.976 \pm 0.026)$ $\mu_N$ using the $\beta$-NMR technique. Results of a shell model calculation in the full \textit{fp} shell model space with the GXPF1 interaction reproduce the experimental value. Together with the known magnetic moment of the mirror partner $^{55}$Co, the isoscalar spin expectation value was extracted as $<\sum \sigma_z >=0.91 \pm 0.07$. The $<\sum \sigma_z>$ shows a similar trend as that established in the \textit{sd} shell. The present theoretical interpretations of both $\mu(^{55}$Ni) and $<\sum \sigma_z>$ for the $T=1/2$, A=55 mirror partners support the softness of the $^{56}$Ni core.