where $\beta_3$ remains large while $\beta_2$ tends to zero. Actually, the wavefunction of the first $1^-$ level extends appreciably in this region, at variance with other levels of the ground-state band.

It would be of great interest, of course, to extend the comparison to the lowest excited band with $K=0$ (the $s=2$ band in the X(5) model notations). Unfortunately, in $^{224}$Th no excited $0^+$ level is known. The non–yrast level schemes of $^{224,226}$Ra will be discussed in the following Section \[S:4.2\]

![\[F:Th\] (Color online) Level scheme of $^{224}$Th, compared with the model predictions for $b=0.85$. Calculated and experimental branching ratios are reported for each level. Experimental data are taken from the NNDC tabulation [@nndc]. Experimental branching ratios from the $7^-$ and $9^-$ levels are not known. Theoretical values of the level energies (in keV) are normalized to that of the $2^+_1$ level; those of the branching ratios are deduced from the matrix elements of Table \[T:30\] with the experimental values of the transition energies. Calculated branches lower than 1% are not shown. ](biz_f7.ps){height="11.cm"}

Electromagnetic transition probabilities
----------------------------------------

Another important test for the model is provided by the E2 transition probabilities. The available experimental information on $B$(E2) values is scarce (only 