Theoretical Study On The Exotic Motions In Nuclei

Symmetry and spontaneous symmetry breaking are fundamental concepts in nature.The atomic nucleus as a many-body quantum system carries a wealth of information on fundamental symmetries and symmetry breaking,which will occur all kinds of nuclear rotation phenomenon and thereby forming exotic rotation modes.The study of exotic rotation modes has been an important issue of nuclear structure.We adopt.the covariant density functional theory(CDFT)and the quantized particle plus rotor model(PRM)to study the antimagnetic rotation bands,chiral doublet bands pseudospin doublet bands and octupole deformed bands of the exotic rotation modes in nuclei,which deepen the cognition about the symmetry and spontaneous symmetry breaking in nuclei.The main work including:(1)Propose the new type of antimagnetic rotation mode.Except for the well-known two-shears mechanism,is it possible that the antimagnetic rotation with more than two shears could exist in a nucleus?We use a fully self-consistent and microscopic tilted-axis cranking model based on covariant density function-al theory to investigate the candidate antimagnetic rotation bands in odd-A 101,103Pd and even-even 102,104Pd.The calculated energy spectra and B(E2)values are in agreement with the available data,which are consistent with the typical characteristics of AMR.The AMR bands in 102,103Pd are suggested for the first,time.By investigating the composition and orientation of the angular momentum,a microscopic picture of the AMR mechanism with four shears is clearly exhibited for the first time.We give the term "umbrella-like antimagnetic rotation"(UAMR)mode to the coupling mechanism.(2)The systematic study of the selection rule for electromagnetic transi-tion in multiple chiral doublet,bands of the different,mass regions.Besides the degenerate excitation energies of the doublet bands,the selection rule for electro-magnetic transitions are considered as more strict criterion for confirming chiral doublet bands.We adopt the one particle one hole plus rotor model to study the selection rule for the multiple chiral doublet,bands with the identical symmetric proton-neutron configurations for the 80.130 and 190 mass regions,respectively.By selecting a suitable basis,the calculated wave functions of MXD are quan?titatively analyzed for the first time and found to meet strict symmetry under the operator A,which is defined as rotation by 90° about the 3-axis with the ex-change of valance proton and neutron.The selection rule for the electromagnetic transitions,namely M1 and E2 t.ransitions are allowed between the levels with different values of A while forbidden between the levels with the same values of A,holds true for the MXD with symmetric proton-neutron configurations.The present results might,be helpful to identify the MXD in experiment.(3)Propose the simultaneous breaking of chiral symmetry and pseudospin symmetry.Chiral symmetry and pseudospin symmetry in nuclei have been significant topic in nuclear structure,the coexistence of chiral symmetry and pseudospin symmetry have not yet been studied.We adopt,the adiabatic a.nd configuration-fixed constrained triaxial covariant,density functional theory(CDFT)and the multiparticle plus rotor model(MPRM)to study the nearly degener-ate triplet bands with the ?g9/2-1(?)vh 11/2(g7/2/-1,d5/2-1)configuration in 105Ag,The/CDFT calculations show the triaxial deformations and the pseudospin Symmetry in the single particle spectra.The MPRM calculations well reproduce the exci-tation energies and the electromagnetic transition probabilities for the triplets.The first and second lowest energy bands of the triplet bands are interpreted as pseudospin doublet bands with the ?g9/2-1(?)vh11/2d5/2-1 and ?g9/2-1(?)vh11/2g7/2-1 configurations,respectivelywhich hold the opposite phase in the B(M1)/B(E2)staggering.The second and third bands are interpreted as chiral doublet band-s with the ?g9/2-1(?)vh11/2d5/2-1 configuration,wlhich show the same phase in the B(M1)/B(E2)staggering.The chiral geometry of the doublet,bands is further conformed by investing the angular momentum components.Such triplet,bands in 105Ag provide the first,example for the siUnultaineou1 breaking of chiral symme-try and pseudospin symmetry in one single nucleus.The present,work will deepen the cognition about the simultaneous breaking of two symmetries in nuclei.