Nuclear Moments of Germanium Isotopes around $N$ = 40

Abstract

Collinear laser spectroscopy measurements were performed on ${}^{69,71,73}$Ge isotopes ($Z=32$) at ISOLDE-CERN. The hyperfine structure of the $4s^{2}4p^2{}^3{P}_1\to 4s^{2}4p5s{}^3{P}_1^o$ 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 $Q_{\mathrm{s}}$ = $-$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 $Q_{\mathrm{s}}$= +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 $N=40$.

Comments: accepted in Phys. Rev. C., in production