Systematic calculations of low-lying states of even-even nuclei within the nucleon pair approximation

A collective S and D nucleon pair approximation of the shell model is applied to even-even Sn, Te, Xe, Ba, and Ce isotopes with mass number A~120--150 and neutron number ranging from 74 to 90. Our Hamiltonian employs monopole pairing, quadrupole pairing plus quadrupole-quadrupole-type interactions between like valence nucleons and quadrupole-quadrupole interactions between valence neutrons and valence protons. With very few parameters, the low-lying states of even-even Sn, Te, Xe, Ba, and Ce isotopes are well described. The calculated B (E2) values and g factors are consistent with recent experimental data. Our systematic calculations also predict B (E2) values and g factors (in particular, for nuclei with valence neutrons in the 82--126 region) if these data are not available.