The dashed lines join the values expected for a rigid rotor. The corresponding values deduced from the parameter free model of Ref. [@lenis06] are (apart for a possible staggering between even and odd $J_i$) almost identical to the rotational ones for large values of $J_i$ ($J_i>7$) and, for decreasing values of $J_i$, their trend reaches a minimum around $J_i=6$ and then increases slightly at lower values of $J_i$. ](biz_f8.ps){height="7.cm"}

We note that, when the transitions to be compared have the same multipolarity, the model predictions are parameter free, or – more exactly – only involve the model parameter $\beta_3^w/\beta_2^w$.

Instead, when the comparison concerns the ratios of the reduced matrix elements for E1 and E2 transitions deexciting the same level, the model predictions include a further normalization factor (the ratio of constants $C_1$ and $C_2$ of Eq.s \[E:14b\],\[E:15\]) which needs to be determined from the experimental data. This comparison is therefore less direct, but it is perhaps more significant, as we shall see in the following.

Results concerning the E1/E2 branches in the ground–state band are shown in the Table \[T:3\] and also depicted in Fig. \[F:e1e2\]. Experimental values of E1/E2 branching ratios in $^{224,226}$Ra and $^{224}$Th include those given 