Unexpected Properties of the Negative-Parity Bands inU236,238,Ra218, andEr156

Analysis of the second differences of the level energies, ${\Delta }^2{E}_{\mathrm{rot}}\mathrm{}\left(I\right)\mathrm{}$, for the negative-parity bands with only odd spins in ${}_{}{}^{236,238}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{218}{}_{}{}^{}\mathrm{Ra}$, and ${}_{}{}^{156}{}_{}{}^{}\mathrm{Er}$ shows, at least for $I>~7$, a $\Delta I=4\mathrm{}$ alternating energy-shift term. Such an unusual signature term is not expected in the framework of the quadrupole deformation model.