  Using a new fast cleaning procedure to prepare isomerically pure ion samples,
we have measured the beta-decay Q_EC values of the superallowed beta-emitters
50Mn and 54Co to be 7634.48(7) keV and 8244.54(10) keV, respectively, results
which differ significantly from the previously accepted values. The corrected
Ft values derived from our results strongly support new
isospin-symmetry-breaking corrections that lead to a higher value of the
up-down quark mixing element, Vud, and improved confirmation of the unitarity
of the Cabibbo-Kobayashi-Maskawa matrix.
