The branching ratios of the collective levels in ${}_{}{}^{128}{}_{}{}^{}\mathrm{Xe}$ were discussed in the framework of the proton-neutron interacting boson model . It is shown that the experiment is only consistent with rather small M1 admixtures among the low-lying collective levels. These small M1 matrix elements imply strong constraints on the proton-neutron interacting boson model Hamiltonian.

• Received 6 February 1986

DOI:https://doi.org/10.1103/PhysRevC.34.1472