Δ I = 1 staggering in octupole bands of light actinides: “Beat” patterns

The $\ensuremath{\Delta}I=1$ staggering (odd-even staggering) in octupole bands of light actinides is found to exhibit a ``beat'' behavior as a function of the angular momentum I, forcing us to revise the traditional belief that this staggering decreases gradually to zero and then remains at this zero value. Various algebraic models [spf-interacting boson model (spdf-IBM), vector boson model, nuclear vibron model] are shown to predict in their su(3) limits constant staggering for this case, being thus unable to describe the ``beat'' behavior. An explanation of the ``beat'' behavior is given in terms of two Dunham expansions [expansions in terms of powers of $I(I+1)]$ with slightly different sets of coefficients for the ground-state band and the negative parity band, the difference in the values of the coefficients being attributed to Coriolis couplings to other negative parity bands. Similar ``beat'' patterns have already been seen in rotational bands of some diatomic molecules, like AgH.