LARGE-BASIS SHELL-MODEL CALCULATION OF THE C-10-]B-10 FERMI MATRIX ELEMENT

We use a 4 (H) over bar Omega shell-model calculation with a two-body effective interaction derived microscopically from the Reid93 potentia l to calculate the isospin-mixing correction for the C-10-->B-10 super allowed Fermi transition. The effective interaction takes into account the Coulomb potential as well as the charge dependence of T=1 partial waves. Our results suggest the isospin-mixing correction delta(c) app roximate to 0.1%, which is compatible with previous calculations. The correction obtained in those calculations, performed in a Oh Omega spa ce, was dominated by deviation from unity of the radial overlap betwee n the converted proton and the corresponding neutron. In the present c alculation this effect is accommodated by the large model space. The o btained delta(c) correction is about a factor of 4 too small to obtain unitarity of the Cabibbo-Kobayashi-Maskawa matrix with the present ex perimental data.