Isospin-dependent Pairing Correlation And The Interacting Birotor Model Of Deformed Nuclei

np-pairing correlation in N～Z nuclei is one of hot topics in nuclear structure study,for which the mean-field plus isospin-dependent pairing model is an important means in under-standing the mechanism and its consequences.On the other hand,it is a great challenge and of importance to provide a unified description of low-lying excitation properties and the excited1⁺states in well-deformed nuclei.In the first part of this thesis,the mean-filed plus isovector pairing model is used to evalu-ate the isovector np-pair occupation number and related quantities in low-lying states of N～Z nuclei in thedsshell.The mean-filed plus isovector and isoscalar pairing O_ST（8）model is also proposed for further investigation of the isovector and isoscalar np-pairing correlation in these nuclei.The results show that the isovector np-pairing contribution to ground state of the odd-odd N=Z nuclei is systematically larger than that in the even-even nuclei,though the isovector np-pair is always non-negligible.Moreover,even though the isoscalar pairing interaction is negligible,both the isoscalar pairing and the isovector pairing are almost of equal importance in low-lying states of the N～Z nuclei,especially in those even-even nuclei with more valence nucleons up to the half-filling.In the second part of this thesis,the interacting birotor model for deformed nuclei is pro-posed in the SU（3）limit of the interacting boson model-II.The model calculation procedure is provided under the coupled SU（3）basis,of which a computation code is compiled.The model is applied to describe positive parity level energies,the related reduced E2 and M1 tran-sition probabilities,electric quarupole and magnetic dipole moments,B（E2;L→L-2）,ΔE=E（L）-E（L-1）,andB（M1;L→L-1）as functions ofin the 1⁺bands with stronger M1 transition strengths,and the moments of inertia foreven and odd branches as functions ofin^156,158,160Gd are calculated and analyzed with comparisons to the experimen-tal data and the results of other theory.Generally speaking,the low-lying level energies,the related reduced E2 and M1 transition probabilities,electric quarupole and magnetic dipole mo-ments are fitted fairly well in following the experimental data patten.Moreover,the even-odd staggering,which is enhanced inB（M1;L→L-1）,occurs in bothΔE=E（L）-E（L-1）andB（M1;L→L-1）in the 1⁺bands with stronger M1 transition strength.However,the deviation in fitting toB(M1;0_g⁺→1_?⁺)is noticeable.There are obvious deviations from the experimental 1⁺level energies with stronger M1 transitions.The M1 strength fragmentation predicted by this model is also insufficient in comparison to that observed in experiments.These defects may be due to the SU（3）limit description adopted with possible collective vibration ne-glected.Furthermore,cross-shell excitations with related configuration mixing are also likely to occur in these 1⁺states,which should also be considered to improve the theory in future work.