| In the framework of the interacting boson-fermion model(IBFM),shape phase transitions and shape coexistence in odd-A nuclei have been analyzed in the mean-field level.By assuming the boson core coupled to a single fermion with j=11/2,we have performed a systematic analysis of the effects of single particle on the system with its core undergoing shape phase transitions of different types including U(5)-SU(3),(U)5-(?),(U)5-O(6) and SU(3)-(?).Specifically,we have investigated the potential configuration for each single-particle state as well as the evolutional behaviors of the classical order parameter in these transitions.The results indicate that the effects of single particle may influence different types of transitions in different ways.For example,the transitional features in the coupled system can be strengthened in some states and weaken in others when the core is undergoing either the U(5)-SU(3)or U(5)-(?) transitions but they will be always weaken when in the U(5)-O(6)transition except for the K=7/2 state,which may keep the same transitional feature as that of the even-even core in all types of shape phase transition.Besides,it is shown that the positions of the critical points in the coupled system can be evidently changed by the effects of single particle in different types of transition,especially the SU(3)-(?) one.More interesting,it is revealed that shape coexistence can clearly emerge in the critical region of the coupled system,which indicates that this feature be taken as a signature of the shape phase transition in odd-A nuclei.A further investigation of the potential structures with the Hamiltoian parameters given by fitting the experimental data indicated that the phenomena of shape phase transitions and shape coexistences should occur in some transitional odd-A nuclei in the A=150 and A=190 region. |
