Measurement of the radiative width of the 12.71-MeV level inC12

The ground-state magnetic dipole transition width of the $1^{+}$ level at 12.71 MeV in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ has been measured to be 0.34±0.05 eV. This value is used to calculate the total width of the level based on a previous measurement of the relative ground-state $\gamma$ width. A total width of 14.6±2.6 eV is thus calculated. A model-dependent measurement of the isospin mixing between this level and the 15.11-MeV level yields the values $\beta =0.19\mathrm{}\pm 0.01$ or 0.05±0.01.