PRAMANA-JOURNAL OF PHYSICS, vol.63, no.5, pp.947-961, 2004 (SCI-Expanded)
Within the quasi-particle random phase approximation (QRPA), the method of the self-consistent determination of the isovector effective interaction which restores a broken isotopic symmetry for the nuclear part of the Hamiltonian is given. The effect of the pairing correlations between nucleons on the following quantities were investigated for the A = 208 nuclei: energies of the isobar analog 0(+) states, the isospin admixtures in the ground state of the even-even nuclei, and the differential cross-section for the Pb-208(He-3,t)Bi-208 reaction at E(He-3) = 450 MeV. Both couplings of the excitation branches with T-z = T-o +/- 1, and the analog state with isovector monopole resonance (IVMR) in the quasi-particle representation were taken into account in our calculations. As a result of these calculations, it was seen that the pairing correlations between nucleons have no considerable effect on the T = 23 isospin admixture in the ground state of the Pb-208 nucleus, and they cause partially an increase in the isospin impurity of the isobar analog resonance (IAR). It was also established that these correlations have changed the isospin structure of the IAR states, and shifted the energies of the IVMR states to the higher values.