Multi-quasiparticle structures up to spin $~$$44\hslash$ in the odd-odd nucleus ${}^{168}\mathrm{Ta}$

High-spin states in the odd-odd nucleus ${}^{168}\mathrm{Ta}$ have been populated in the ${}^{120}\mathrm{Sn}$(${}^{51}\mathrm{V}$,3$n$) reaction. Two multi-quasiparticle structures have been extended significantly from spin $~20\hslash$ to above $40\hslash$. As a result, the first rotational alignment has been fully delineated and a second band crossing has been observed for the first time in this nucleus. Configurations for these strongly coupled rotational bands are proposed based on signature splitting, $B(M1)/B(E2)$ ratio information, and observed rotation-alignment behavior. Properties of the observed bands in ${}^{168}\mathrm{Ta}$ are compared to related structures in the neighboring odd-$Z$, odd-$N$, and odd-odd nuclei and are discussed within the framework of the cranked shell model.

Figure 1

Level scheme of ${}^{168}\mathrm{Ta}$ resulting from the present work. All spin and parity assignments are tentative (labels are put in parentheses) and are based on the proposed configurations. The states and transitions drawn as dashed lines are tentative. See text for details.

Figure 2

Coincidence spectra representative of bands 1 (top) and 2 (bottom) in ${}^{168}\mathrm{Ta}$. These summed spectra were obtained by triple gating on selected in-band transitions, $267\to 1017$ and $472\to 1033$ of band 1 and $381\to 1117$ and $317\to 973$ of band 2 (in keV). The highest-energy $\gamma$ rays observed in these bands are given in the insets. Transitions are labeled by their energies in keV. The labels with the “number(number)” format denote $\gamma$-ray multiplets, such as “479(477)” pointing to the 479-keV transition mixed with the 477-keV line, for example.

Figure 3

The energy staggerings $E(I)-[E(I+1)+E(I-1)]/2$ as a function of spin $I$ for the available $\pi h_{11/2}[514]9/2\otimes \nu i_{13/2}[642]5/2$ bands in the odd-odd nuclei neighboring ${}^{168}\mathrm{Ta}$ and band 1 in ${}^{168}\mathrm{Ta}$. The $\alpha =0$ and $\alpha =1$ states are denoted with solid and open symbols, respectively. Inversion points are marked with red arrows. See text for details.

Figure 4

The energy staggerings $E(I)-[E(I+1)+E(I-1)]/2$ as a function of spin $I$ for the available $\pi d_{5/2}[402]5/2\otimes \nu i_{13/2}[642]5/2$ and $\pi g_{7/2}[404]7/2\otimes \nu i_{13/2}[642]5/2$ bands in the odd-odd nuclei neighboring ${}^{168}\mathrm{Ta}$ and band 2 in ${}^{168}\mathrm{Ta}$. The $\alpha =0$ and $\alpha =1$ states are denoted with solid and open symbols, respectively. See text for details.

Figure 5

Measured $B(M1)/B(E2)$ ratios as a function of spin for bands 1 (top) and 2 (bottom) in ${}^{168}\mathrm{Ta}$. Solid (open) symbols denote the signatures $\alpha =1(0)$. Theoretical calculations are displayed as lines with the following configurations in the top panel: (1) $\pi [514]9/2\otimes \nu [642]5/2$, (2) $\pi [514]9/2\otimes \nu [642]5/2\mathit{BC}$; and in the bottom panel: (1) $\pi [402]5/2\otimes \nu [642]5/2$, (2) $\pi [402]5/2\otimes \nu [642]5/2\mathit{BC}$, (3) $\pi [404]7/2\otimes \nu [642]5/2$, (4) $\pi [404]7/2\otimes \nu [642]5/2\mathit{BC}$. See Table (and Fig. 8) for the definition of $\mathit{BC}$. See text for details.

Figure 6

Experimental alignments for band 1 in ${}^{168}\mathrm{Ta}$, the $\nu i_{13/2}$ band in ${}^{167}\mathrm{Hf}$, and the $\pi h_{11/2}$ band in ${}^{167}\mathrm{Ta}$ as a function of the rotational frequency. A reference with the common $J_0$ and $J_1$ Harris parameters indicated in the figure was subtracted for each band. Solid (open) symbols denote the signatures $\alpha =+\frac{1}{2}$($-\frac{1}{2}$) or 1(0). Tentative transitions are excluded from the figure. See text for details.

Figure 7

Experimental alignments for band 2 in ${}^{168}\mathrm{Ta}$, the $\nu i_{13/2}$ band in ${}^{167}\mathrm{Hf}$, and the $\pi d_{5/2}$ band in ${}^{167}\mathrm{Ta}$ as a function of the rotational frequency. A reference with the common $J_0$ and $J_1$ Harris parameters given in the figure was subtracted for each band. Solid (open) symbols denote the signatures $\alpha =+\frac{1}{2}$($-\frac{1}{2}$) or 1(0). Tentative transitions are excluded from the figure. See text for details.

Figure 8

Quasineutron Routhians for ${}^{168}\mathrm{Ta}$ calculated in the CSM with deformation parameters of ${\beta }_2=0.24$, ${\beta }_4=0$, and $\gamma =0$. The four line types denote four combinations of (parity, signature): solid ($+$,$+1/2$), dot ($+$,$-1/2$), dash-dot ($-$,$+1/2$), dash ($-$,$-1/2$). See text for details.

Figure 9

Quasiproton Routhians for ${}^{168}\mathrm{Ta}$ calculated in the CSM with deformation parameters of ${\beta }_2=0.24$, ${\beta }_4=0$, and $\gamma =0$. The convention for drawing the lines is same as that used in Fig. 8. See text for details.