Low-lying isovector collective states and the interacting-boson model

Isovector low-lying collective $2^{+}$ states are studied in the Samarium isotopes in terms of the interacting-boson model. On the basis of E2 transition data, it is pointed out that the $2_3^{+}$ states of ${}_{}{}^{148}{}_{}{}^{}$,150Sm are isovector. The first calculation including different proton and neutron boson charges is reported for the E2 transitions $0_1^{+}$→$2_1^{+}$. $2_2^{+}$, and $2_3^{+}$ of ${}_{}{}^{148154}{}_{}{}^{}\mathrm{Sm}$, giving rise to the first comprehensive agreement with experiment. Some predictions of B(M1) values are presented for further confirmation of the isovector properties.