Study of nuclear deformation by boson models

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The following points have been clarified in this research project. (1) The phase transition between spherical and deformed shapes is studied in terms of the sdg boson model, by taking Samarium isotopes. It has been indicated that the phase transition produces a clear effect on M1 excitation strength. This kind of studies have been extended to Polonium, Radium, etc. It has been shown what Pauli effect should appear in E2 transition strength throughout this phase transition. (2) Octupole deformation has been studied in terms of the spdf boson model. (3) Triaxial deformation has been investigated in terms of the sd boson model. The relation between level compression and gamma unstable deformation was studied with analytic expressions for O(6) symmetry.Besides these studies, the structure of odd mass nuclei has been studied in terms of the Interacting Boson-Fermion Model. The moment of inertia of high-spin states has been studied with a simple expression for its variation for even-even nuclei. Superdeformation has been described by introducing an extended model of the Interacting Boson Model. The E2 decay out of superdeformed bands was suggested. Mixed-symmetry states have been invesigated for Ion, Cadmium and Barium isotopes. The relations between chaos and symmetries have been studied in terms of the shell model and the boson model. The nuclear rotation has been discussed from the viewpoint of quantal coupling of proton and neutron bodies.Thus, various aspects of the nuclear collective motion have been studied, providing us with deeper understandings.