Spectroscopic study of the possibly triaxial transitional nucleus ${}^{\mathbf{75}}\mathbf{Ge}$

The collective structures of ${}^{75}\mathrm{Ge}$ have been studied for the first time via the ${}^{74}\mathrm{Ge}(\alpha ,2p1n){}^{75}\mathrm{Ge}$ fusion-evaporation reaction. Two negative-parity bands and one tentative positive-parity band built on the $\nu p_{1/2},\nu f_{5/2}$, and $\nu g_{9/2}$ states, respectively, are established and compared with the structures in the neighboring $N=43$ isotones. According to the configuration-constrained potential-energy surface calculations, a shape transition from oblate to prolate along the isotopic chain in odd-$A$ Ge isotopes is suggested to occur at ${}^{75}\mathrm{Ge}$. The properties of the bands in ${}^{75}\mathrm{Ge}$ are analyzed in comparison with the triaxial particle rotor model calculations.

Figure 1

Coincident $\gamma$-ray spectrum gated on the 252.8-keV transition. For convenience to see, transitions of ${}^{75}\mathrm{Ge}$ are marked as red. The peaks marked with stars are known contaminants.

Figure 2

Coincident $\gamma$-ray spectra double gated on the (a) 252.8- and 203.9-keV transitions, (b) 176.5- and 334.2-keV transitions, (c) 176.5- and 742.3-keV transitions, (d) 60.0- and 787.0-keV transitions. The transitions of ${}^{75}\mathrm{Ge}$ are marked as red. The peaks marked with stars are known contaminants.

Figure 3

Partial level scheme of ${}^{75}\mathrm{Ge}$. The energies are given in keV, and the widths of the arrows are proportional to their relative intensities.

Figure 4

Comparison of the $\nu p_{1/2},\nu f_{5/2}$, and $\nu g_{9/2}$ bands in isotones ${}^{75}\mathrm{Ge},{}^{77}\mathrm{Se}$ [27], and ${}^{79}\mathrm{Kr}$ [29].

Figure 5

The calculated PESs for ground states in (a) ${}^{73}\mathrm{Ge}$ and (b) ${}^{75}\mathrm{Ge}$. The energy contours are at 100-keV intervals. The corresponding minima are $({\beta }_2=0.23,\gamma =-{41}^{\circ }),({\beta }_2=0.17,\gamma =-{19}^{\circ })$.

Figure 6

The calculated energy spectra $E\left(I\right)$ for the (a) $\nu g_{9/2}$, (b) $\nu p_{1/2}$, and (c) $\nu f_{5/2}$ bands in ${}^{75}\mathrm{Ge}$ by the PRM in comparison with the experimental data.