Collinear laser spectroscopy measurements were performed on ${}^{69,71,73}\mathrm{Ge}$ 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 by using state-of-the-art atomic relativistic Fock-space coupled-cluster method. A new ${}^{73}\mathrm{Ge}$ quadrupole moment was determined from these calculations and previously measured precision hyperfine parameters, yielding $Q_{\mathrm{s}}=-0.198\left(4\right)$ b, in excellent agreement with the literature value from molecular calculations. The moments of ${}^{69}\mathrm{Ge}$ have been revised: $\mu =+0.920\left(5\right){\mu }_N$ and $Q_{\mathrm{s}}=+0.114\left(8\right)\mathrm{b}$, and those of ${}^{71}\mathrm{Ge}$ 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 $N=40$.

• Received 30 September 2020
• Accepted 2 November 2020

DOI:https://doi.org/10.1103/PhysRevC.102.054331

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Published by the American Physical Society