Test of the Standard Electroweak Model in superallowed 0^+ -> 0^+ nuclear β decays

Precise measurements of superallowed β decays provide demanding test of the fundamental symmetries of the electroweak interaction. Collectively, the corrected comparative half-lives of these transitions allow a sensitive probe of the CVC hypothesis. Moreover, by providing the most accurate determination of V_ud, the up-down quark-mixing element, these data serve as a stringent test of the unitarity of the CKM matrix of the Standard Model. However, prior to new results, the sum of squares of the top-row CKM elements failed to meet unity by more than 2 σ. As a possible explanation for this default, uncertainties in the Coulomb corrections applied to the experimental data were pointed out. It became therefore essential to extend the study to heavy odd-odd (A >= 62) and medium mass (18 <= A <= 42) nuclei where these corrections are predicted to be much larger. In this context, the β-γ decays of ^62Ga and ^38Ca have been investigated at the IGISOL and ISOLDE facilities. The results obtained will be presented. Prospects for the continuation of this work will be also discussed. )