Application of the Dyson boson mapping to the analysis of the phase transition at N=88-90

The Dyson boson mapping theory is applied to the analysis of the phase transition from vibrational to rotational spectra in the Sm isotopes. The original quasiparticle space consisting of multi-quadrupole collective-phonon states on the spherical shell-model bases is transformed into a boson space by the Dyson mapping. In this boson space, numerical analysis is carried out for 146-154Sm. In addition, the boson space is extended to contain non-collective phonon degrees of freedom and in this extended space the coupling effect between collective and non-collective phonons is precisely estimated. The numerical results show that the contribution from the noncollective phonon degrees of freedom cannot be neglected in the transitional region. (orig.)