Shears bands in $^{204}$At and $^{206}$Fr?

Excited states above the (10$^{-})$ isomers in the N = 119 isotones $^{204}$At and $^{206}$Fr have been observed for the first time. The experimental setup consisted of Gammasphere and the evaporation-residue detector Hercules. A beam-target combination of $^{30}$Si + $^{181}$Ta (E$_{lab}$ =152 MeV) was utilized for 20 hours in order to obtain these data (via the $\alpha $3n and 5n channels, respectively). Both nuclides display a sequence of transitions with $\gamma $-ray energies between 130 and 300 keV. These structures are similar to the shears bands observed primarily in Pb nuclei [1]; however, the dipole character of the $\gamma $-rays must be verified. Alignment plots for the band structures indicate that a crossing occurs at a relatively low frequency of $\omega \quad \approx $ 0.23 MeV. This is in contrast with the shears bands in the N = 119 Bi and Pb nuclei where no crossings are observed, and in N $<$ 119 Pb nuclei where crossings are normally found at $\omega \quad \approx $ 0.30 MeV. Possible interpretations of the nature of this crossing will be discussed. [1] R.M. Clark and A.O. Macchiavelli, Annu. Rev. Nucl. Part. Sci. 501, 1 (2001).