The Interacting Boson Model Realization Of The Two-rotor

The Interacting Boson Model(IBM)is one of successful theoretical models in describing low energy spectra of atomic nuclei.In focusing on many excited 1+ states of even-even nuclei in the rare-earth and actinide regions,which can not be described by the original interacting boson model(IBM-?)in treating both types of nucleons the same,the proton-neutron interacting boson model(IBM-?)is adopted.The IBM-? realization of the two-rotor is estab-lished and used to describe low energy spectrum and electromagnetic transition properties of nuclei in the rare-earth and actinide regions.In this thesis,under the coupled SU(3)basis of the proton-neutron interacting boson model,the two-rotor model is constructed in the IBM-? framework based on the IBM SU(3)realization of the rotor.A computation code of the model is compiled and used to fit low energy spectrum,reduced E2 transition probabilities,electric quadrupole moments,reduced M1 transition prob-abilities,and magnetic moments of deformed nuclei in the rare-earth and actinide regions,for which 156Gd is taken as an example of the model applications.The theoretical results of the model are then compared with the corresponding experimental data.The results show that the model describes the low-lying excited levels,reduced E2 transi-tion probabilities,electric quadrupole moments,reduced M1 transition probabilities,and mag-netic moments of 156Gd rather well.The theoretical B(E2)values are in good agreement with the experimental ones.Though the model results of 1+ level energies are not in one-to-one cor-respondence with experimentally observed ones,there are indeed a number of 1+ levels within 2-4 MeV with two strong M1 transitions around 3 MeV to the ground state as observed in experiments.The theoretical sum rule of reduced M1 transition rates for the transitions from ground state to all excited 1+ states are close to the experimental value.The results thus show that this model seems suitable in describing low energy spectra and electromagnetic proper-ties of well deformed nuclei in the rare-earth and actinide regions.Further improvements of the model may be achieved to reproduce better fitting results of excited 1+ states within 2-4 MeV region qualitatively in taking the fourth order rotor term into consideration,which will be considered in future wrok.