Interacting boson-fermion model analysis of beta decay in A=195 and 197 nuclei

The interacting boson-fermion model is used to analyze beta decay. The beta transition operator in the boson-fermion space is constructed with the parameters obtained from microscopic considerations. The ft values are calculated for the first nonunique forbidden transitions between states based on natural parity orbitals in the decays of ¹⁹⁵Pt, ¹⁹⁵Pt, ¹⁹⁵Au, ¹⁹⁷Au, and ¹⁹⁷Au. The structure of the odd-neutron nuclei is described in the U(6)⊗U(12) boson-fermion symmetry limit. For the odd-proton nuclei, three different approaches, in particular the U(6)⊗U(4) symmetry, the U(6)⊗U(20) symmetry, and the perturbed U(6)⊗U(4) scheme, are compared. The calculated ft values are very sensitive to details of nuclear wave functions, the best results being obtained with the perturbed U(6)⊗U(4) scheme. Phase ambiguities in nuclear wave functions can be disentangled from beta decay analysis. The exchange terms in the boson-fermion transition operator, which take into account the Pauli principle between the odd-nucleon and nucleons forming the even-even collective core, proved to be quite important.