Beta decay of odd-mass nuclei in the interacting boson-fermion model

The accurate prediction of beta decay rates requires a detailed knowledge of nuclear structure properties of both the initial and final nuclei. Since exact calculations for medium mass and heavy systems are impossible, some approximation scheme is necessary. From spectroscopic studies it turns out that the proton-neutron interacting boson-fermion model is able to successfully describe a broad class of nuclei comprising spherical and deformed shapes. In this framework Gamow-Teller matrix elements are computed and compared with the experimental ones for many isotopic chains, ranging from tellurium to lanthanum in the N = 50-82 neutron shell. The mass dependence of the observed hindrance is reproduced correctly and the results show a quantitative improvement with respect to pairing theory. The strength distribution over low-lying states is also studied and it is found that a quenching factor of ∼3.5 incorporates the effects due to the truncation of the large configuration space