Isovector effective charge and the staggering of2+→0+transition probabilities in the titanium isotopes

In an effort to understand the magical status of $N=32$ and $N=34$ at the very neutron rich edge, experiments have been carried out in the titanium isotopes up to $A=56$. The measured staggering of the $B(E2)$'s is not reproduced by the shell model calculations using the best effective interactions. We argue that this may be related to the choice of the isovector effective charge and to the value of the $N=34$ neutron gap.