Multiple band structures in ${}^{70}\mathbf{Ge}$

High-spin states in ${}^{70}\mathrm{Ge}$ were studied using the ${}^{55}\mathrm{Mn}$(${}^{18}\mathrm{O},p2n$) fusion-evaporation reaction at a beam energy of 50 MeV. Prompt $\gamma \text{−}\gamma$ coincidences were measured using the Florida State University Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. An investigation of these coincidences resulted in the addition of 31 new transitions and the rearrangement of four others in the ${}^{70}\mathrm{Ge}$ level scheme, providing a more complete picture of the high-spin decay pattern involving both positive- and negative-parity states with multiple band structures. Spins were assigned based on directional correlation of oriented nuclei ratios, which many times also led to unambiguous parity determinations based on the firm assignments for low-lying states made in previous work. Total Routhian surface calculations, along with the observed trends in the experimental kinematic moment of inertia with rotational frequency, support the multiquasiparticle configurations of the various crossing bands proposed in recent studies. The high-spin excitation spectra predicted by previous shell-model calculations compare favorably with the experimental one determined from this study.

Figure 1

Partial level scheme of ${}^{70}\mathrm{Ge}$ based on its population at high spin in the present work. Transitions and states shown in red (light gray) are new to this work, while those indicated in black have been verified from previous investigations. Transitions and states with either rearranged placements or new assignments compared with previous work are shown in blue (light gray). The numbers above each band sequence serve as labels used to facilitate the discussion in the text.

Figure 2

A portion of the ${90}^{\circ }$ background-subtracted coincidence spectra obtained by gating on 840- (top) and 1179-keV (bottom) $\gamma$ rays. The 901.8-keV line is labeled in red (or light gray) to indicate that it is a new transition in the ${}^{70}\mathrm{Ge}$ level scheme determined from this work.

Figure 3

A portion of the ${90}^{\circ }$ background-subtracted coincidence spectra obtained by gating on 744- (top) and 1099-keV (bottom) $\gamma$ rays. New transitions in the ${}^{70}\mathrm{Ge}$ level scheme, as determined from this work, have their energies labeled in red (or light gray).

Figure 4

A portion of the ${90}^{\circ }$ background-subtracted coincidence spectra obtained by gating on 854-keV $\gamma$ rays. New (rearranged) transitions in the ${}^{70}\mathrm{Ge}$ level scheme, as determined from this work, have their energies labeled in red (blue) or light gray.

Figure 5

Sample total Routhian surfaces in the $({\beta }_2,\gamma )$ plane for the vacuum configuration in ${}^{70}\mathrm{Ge}$ at rotational frequencies of $\hslash \omega =0$ (top), 0.5 (middle), and 0.8 MeV (bottom). The spacing between contour lines is 200 keV.

Figure 6

Experimental kinematic moments of inertia $J^{\left(1\right)}$ as a function of rotational frequency for the ground-state band and its progression to even-spin yrast (yrare) bands based on the $8_1^{+}$ ($8_2^{+}$) state in ${}^{66}\mathrm{Ge}$ [17], ${}^{68}\mathrm{Ge}$ [18], ${}^{70}\mathrm{Ge}$, and ${}^{72}\mathrm{Ge}$ [3], as indicated in the upper (lower) panel. Filled (open) symbols represent transitions with yrast (yrare) parent states. A common value of $K=0$ was used for each band.

Figure 7

Static moment-of-inertia parameter $\mathcal{I}$ as a function of spin $J$ for the $\gamma$-vibrational bands in ${}^{66}\mathrm{Ge}$ [17], ${}^{68}\mathrm{Ge}$ [18], ${}^{70}\mathrm{Ge}$, ${}^{72}\mathrm{Ge}$ [3], ${}^{74}\mathrm{Ge}$ [45], and ${}^{76}\mathrm{Ge}$ [1].

Figure 8

Energy staggering parameter $S\left(J\right)$ as a function of spin $J$ for the $\gamma$-vibrational bands in ${}^{66}\mathrm{Ge}$ [17], ${}^{68}\mathrm{Ge}$ [18], ${}^{70}\mathrm{Ge}$, ${}^{72}\mathrm{Ge}$ [3], ${}^{74}\mathrm{Ge}$ [45], and ${}^{76}\mathrm{Ge}$ [1]. Filled (open) symbols represent $S\left(J\right)$ values associated with even (odd) $J$.

Figure 9

Experimental kinematic moments of inertia $J^{\left(1\right)}$ as a function of rotational frequency for the negative-parity bands based on the $3^{-}$ octupole state (top panel), as well as for the lowest even-spin negative-parity bands (bottom panel), in ${}^{66}\mathrm{Ge}$ [17], ${}^{68}\mathrm{Ge}$ [18], ${}^{70}\mathrm{Ge}$, and ${}^{72}\mathrm{Ge}$ [3]. A common value of $K=3$ was used in each band.

Figure 10

Sample total Routhian surfaces in the $({\beta }_2,\gamma )$ plane for the lowest two-quasiproton configuration in ${}^{70}\mathrm{Ge}$ representing states with $\pi =-$ and $\alpha =1$ at rotational frequencies of $\hslash \omega =0$ (top), 0.5 (middle), and 0.8 MeV (bottom). The spacing between contour lines is 200 keV.