Mechanism of Separate Neutron and Proton Excitations in Interacting Neutron and Proton Boson Model and ¹⁶⁸Er Spectrum

We study the interacting neutron and proton boson model (IBM2) model without the assumption of the maxium F-spin truncation. Then we make a complete IBM2 calculation of the spectrum and E2 transitions to the ¹⁶⁸Er nucleus. Also from our simple condensate wavefunctions, we investigate a new mechanism of separate excitations of neutron and proton boson degrees.