A measurement of the superallowed $0^{+}\to 0^{+}$ branching ratio in ${}^{10}$C performed with the $8\pi$ gamma-ray spectrometer is described. From the measured branching ratio, we extract a new precise value of $Ft{(}^{10}\mathrm{C})=3076.7\mathrm{}(6.0)\mathrm{s}$. This does not support previously suggested $Z$- or $Z^2$-dependent corrections to the superallowed $0^{+}\to 0^{+}$ data set, which removed the apparent nonunitarity of the Cabibbo-Kobayashi-Maskawa matrix.

• Received 7 October 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.1521