Description of β decay to excited quadrupole phonon states within a boson-expansion formalism

A microscopic Hamiltonian including realistic two-body interaction, is used to describe the single {β} Gamow-Teller transitions to the ground state, the first excited quadrupole state (2₁⁺) and the two-quadrupole-phonon states (0_2-ph⁺,2_2-ph⁺) of even-even isotopes 118,120Sn from the two adjacent odd-odd nuclei 118,120In and 118,120Sb. The higher-RPA effects are evaluated within a boson-expansion formalism. The transition amplitudes are studied as functions of the particle-particle interaction strength. The corresponding logft_± values are also calculated and compared with experimental data as well as with the predictions of some previous calculations. The perturbative components of the states involved give important contribution to the transitions feeding the two-phonon states. Adding these, the agreement with the experimental data is improved. {} 1996 The American Physical Society.