Based on the boson expansion and the so-calkd Jancovici-Schiff substitution, and approach has been developed to study the microscopic foundation of the interacting boson model. In this work an extension of theapproach is made, thus one is able to treat the excitations of such system in which several neutron bosons, a proton boson and a proton-hole boson exist. With the consideration of the proton two-particle twohole excitation configurations we have studied the intruder quasi-rotational bands in double-even Sn nuclei. The Calculated results are compared with ex...
