Study On Structures Of N=126 Isotones Based On The Nucleon-pair Approximation With Particle-hole Excitations

Atomic nuclei are complex quantum many-body systems consisting of protons and neutrons.The shell model is a microscopic many-body theory for studies on structures of low-lying states of nuclei.However,when it comes to particle-hole excitations arising from two major shells,the configuration space is too large to handle,thus it is necessary to truncate the configuration space.Because in the scale of nuclei the dominant component of the nucleon-nucleon interaction is short-range and attractive,the pair truncation is a natural and effective strategy.In the nucleon-pair approximation of the shell model,low-energy collective pairs with definite angular momenta and parities are used to construct the configuration space to truncate the full shell-model space.In this thesis,we study low-lying states of two N=126 isotones 210Po and 212Rn using the nucleon-pair approximation with particle-hole excitations.In the calculation,we adopt the low-momentum interaction Vlow-k renormalized from the CD-Bonn potential,and consider valence proton particles in the 82-126 major shell and neutron particle-hole excitations across the N=126 shell gap.The calculated energy levels,quadrupole transition probabilities B(E2)s,and octupole transition probabilities B(E3)s,well reproduce the experimental data.We focus on negative-parity states,where either/both the configurations of neutron one-particle-one-hole(lplh)excitations across the N=126 shell gap or/and the nonzero-seniority configurations of valence proton particles involving the 0i13/2 orbit play a crucial role.We calculate the probability of neutron particle-hole excitation across the N=126 shell gap.The results indicate that most of the low-lying states of 210Po and 212Rn are dominated by the configurations of valence proton particles coupled to the N=126 closed shell;Meanwhile,the 1211-,131-,141-states of 210Po and the 1911-state of 212Rn are dominated by the configurations of valence proton particles with nonzero seniority numbers,coupling with the neutron lplh excitations across the N=126 shell gap.We take ?E1=E(121-)-E(81+)and ?E2=E(131-)-E(81+)of 210Po and?E3=E(19-1)-E(141+)of 212Rn to represent excitations energies of corresponding neutron particle-hole excitations.The results suggest that the calculation where the N=126 shell gap is taken to be 2.83MeV,very well reproduce the experimental results.