Band crossing and shape evolution in ${}^{73}\text{Ge}$

The spectroscopy of ${}^{73}\text{Ge}$ has been investigated via the ${}^{70}\text{Zn}({}^7\text{Li},3np){}^{73}\text{Ge}$ fusion-evaporation reaction. A previously known band built on the $\nu \left(f_{5/2}\right)$ orbital is extended up to higher-spin states and a new rotational band built on the $\nu \left(g_{9/2}\right)$ orbital is established. The observed band crossing and shape evolution induced by the alignment in ${}^{73}\text{Ge}$ are studied in comparison with the similar structures in the neighboring $N=41$ isotones and the cranked Woods–Saxon–Strutinsky calculations by means of total-Routhian-surface (TRS) methods. The inversion of the order of the $g_{9/2}$ neutron and the $g_{9/2}$ proton crossing frequency observed in the negative-parity $\nu \left(f_{5/2}\right)$ bands between ${}^{73}\text{Ge}$ and ${}^{75}\text{Se}$, ${}^{77}\text{Kr}$ can be ascribed to their different triaxial deformations. At higher spins, both the $\nu \left(f_{5/2}\right)$ and $\nu \left(g_{9/2}\right)$ bands in ${}^{73}\text{Ge}$ undergo a shape evolution with sizable alignments occurring. The characters of large signature splitting in $\nu \left(g_{9/2}\right)$ band of ${}^{73}\text{Ge}$ are discussed.

Figure 1

Coincident $\gamma$-ray spectra with gating on (a) 825.4 keV and (b) 873.4 keV transitions. The peaks marked with stars are known contaminants from other nuclei, and the peak marked with the triangle is the deexcited transition from individual level of ${}^{73}\text{Ge}$ which is not included in the partial level scheme of Fig. 2.

Figure 2

Partial level scheme of ${}^{73}\text{Ge}$. Energies are in keV.

Figure 3

The kinematic moments of inertia as a function of rotational frequency for (a) the negative-parity $\nu \left(f_{5/2}\right)$ bands and (b) the positive-parity $\nu \left(g_{9/2}\right)$ bands in $N=41$ isotones ${}^{73}\text{Ge}$, ${}^{75}\text{Se}$, and ${}^{77}\text{Kr}$. The data of ${}^{75}\text{Se}$ were taken from Refs. [21, 22, 23], and the data of ${}^{77}\text{Kr}$ were taken from Refs. [26, 27, 28].

Figure 4

Experimental and calculated moments of inertia for (a) the negative-parity $\nu \left(f_{5/2}\right)$ band and (b) the positive-parity $\nu \left(g_{9/2}\right)$ band in ${}^{73}\text{Ge}$.

Figure 5

Calculated TRSs for the ($\pi =-$, $\alpha =+1/2$) [(a) $\hslash \omega =0.35\mathrm{MeV}$, (b) $\hslash \omega =0.55\mathrm{MeV}$, and (c) $\hslash \omega =0.95\mathrm{MeV}$] and ($\pi =+$, $\alpha =+1/2$) [(d) $\hslash \omega =0.35\mathrm{MeV}$, (e) $\hslash \omega =0.55\mathrm{MeV}$, and (f) $\hslash \omega =0.95\mathrm{MeV}$] sequences in ${}^{73}\text{Ge}$. The energy contours are at 200 keV intervals.

Figure 6

Experimental $\left[E\right(I)-E(I-1\left)\right]/2I$ as a function of angular momentum for the positive-parity $\nu \left(g_{9/2}\right)$ bands in isotones ${}^{73}\text{Ge}$, ${}^{75}\text{Se}$, and ${}^{77}\text{Kr}$. The data of ${}^{75}\text{Se}$ were taken from Refs. [21, 22, 23], and the data of ${}^{77}\text{Kr}$ were taken from Refs. [26, 27, 28].