First observation of rotational structures in ${}^{168}\mathrm{Re}$

The first rotational sequences have been assigned to the odd-odd nucleus ${}^{168}\mathrm{Re}$. Coincidence relationships of these structures with rhenium x rays confirm the isotopic assignment, while arguments based on the $\gamma$-ray multiplicity ($K$-fold) distributions observed with the new bands lead to the mass assignment. Configurations for the two bands were determined through analysis of the rotational alignments of the structures and a comparison of the experimental $B\left(M1\right)/B\left(E2\right)$ ratios with theory. Tentative spin assignments are proposed for the $\pi h_{11/2}\nu i_{13/2}$ band, based on energy level systematics for other known sequences in neighboring odd-odd rhenium nuclei, as well as on systematics seen for the signature inversion feature that is well known in this region. The spin assignment for the $\pi h_{11/2}\nu (h_{9/2}/f_{7/2})$ structure provides additional validation of the proposed spins and configurations for isomers in the ${}^{176}\mathrm{Au} \to {}^{172}\mathrm{Ir}\to {}^{168}\mathrm{Re} \alpha$-decay chain.

Figure 1

Level scheme for ${}^{168}\mathrm{Re}$ from the present analysis. Since no direct measurements of spin or parity have been performed, all assignments are based on systematic arguments, as discussed in the text and, thus, must be considered tentative.

Figure 2

(a) Coincidence spectrum of band 1 in ${}^{168}\mathrm{Re}$ resulting from the sum of all combinations of triple gates in the hypercube using the dipole transitions between the ${12}^{-}$ and ${20}^{-}$ states, except for the 295-keV transition. The inset displays the high-energy portion of the same spectrum. (b) Spectrum of band 2 which was produced in a similar manner as panel (a), where all combinations of triple gates using the dipole transitions between the ${16}^{+}$ and ${23}^{+}$ states were summed together. Once again, the inset displays the high-energy region of the same spectrum.

Figure 3

Normalized $K$-fold distributions (see text for definition) for events associated with strongly coupled bands in ${}^{169}\mathrm{Re}$ and ${}^{170}\mathrm{Re}$, as well as the sequence labeled as band 1 in Fig. 1. The lower $K$-fold distribution for band 1 indicates that it is associated with the $5n$ reaction channel, leading to the assignment of the structure to ${}^{168}\mathrm{Re}$.

Figure 4

Alignments of bands 1 and 2 in ${}^{168}\mathrm{Re}$. The Harris parameters used are discussed in the text. In addition, the $\nu i_{13/2}$ and $\nu (h_{9/2}/f_{7/2})$ bands from ${}^{167}\mathrm{W}$ are plotted for reference.

Figure 5

Experimental and theoretical $B\left(M1\right)/B\left(E2\right)$ ratios for the decay sequences in ${}^{168}\mathrm{Re}$. Parameters for the theoretical calculations are discussed in the text and given in Table 2.

Figure 6

Energy levels of the lowest $\pi h_{11/2}\nu i_{13/2}$ states in the lightest odd-odd rhenium nuclei.

Figure 7

Signature splitting function, $S\left(I\right)$, as defined in the text, versus spin for $\pi h_{11/2}\nu i_{13/2}$ bands. Even spins (odd spins) are denoted with filled (open) circles. The reversion spins (as defined in text) are also labeled.