Nuclear Moments of Germanium Isotopes around $N$ = 40

TL;DR

This study used laser spectroscopy and advanced atomic calculations to measure and analyze nuclear moments of germanium isotopes near neutron number 40, revealing insights into their nuclear structure and shape evolution.

Contribution

It provides new measurements of nuclear moments for germanium isotopes and interprets these results with large-scale shell-model calculations, highlighting structural changes around N=40.

Findings

New quadrupole moment for 73Ge consistent with molecular calculations

Revised magnetic and quadrupole moments for 69Ge and confirmed for 71Ge

Evidence of structural transition from single-particle to deformed shapes near N=40

Abstract

Collinear laser spectroscopy measurements were performed on $^{69,71,73}$Ge isotopes ($Z = 32$) at ISOLDE-CERN. The hyperfine structure of the $4s^2 4p^2 \, ^3P_1 \rightarrow 4s^2 4p 5s \, ^3P_1^o$ transition of the germanium atom was probed with laser light of 269 nm, produced by combining the frequency-mixing and frequency-doubling techniques. The hyperfine fields for both atomic levels were calculated using state-of-the-art atomic relativistic Fock-space coupled-cluster calculations. A new $^{73}$Ge quadrupole moment was determined from these calculations and previously measured precision hyperfine parameters, yielding $Q_{\rm s}$ = $-$0.198(4) b, in excellent agreement with the literature value from molecular calculations. The moments of $^{69}$Ge have been revised: $\mu$ = +0.920(5) $\mu_{N}$ and $Q_{\rm s}$= +0.114(8) b, and those of $^{71}$Ge have been confirmed. The experimental moments around $N = 40$ are interpreted with large-scale shell-model calculations using the JUN45 interaction, revealing rather mixed wave function configurations, although their $g$-factors are lying close to the effective single-particle values. Through a comparison with neighboring isotones, the structural change from the single-particle nature of nickel to deformation in germanium is further investigated around $N = 40$.