Isospin-Nonconserving Decays in Mirror Nuclei

We have measured branching ratios for the isospin-nonconserving particle decays of the 15.1-MeV $T=\frac{3}{2}$ states in ${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ to the (0.0, $0^{+}$) and (4.44, $2^{+}$) states of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. By comparing ratios of reduced widths with the $0^{+}$ and $2^{+}$ states of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ for the mirror decays, we show that the form of the isospin impurity in the 15.1-MeV states depends on $T_z$.