We have deduced compound nuclear isospin mixing in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}_{}^{\mathrm{*}}{}_{}{}^{}$ and ${}_{}{}^{26}{}_{}{}^{}\mathrm{Al}_{}^{\mathrm{*}}{}_{}{}^{}$ at excitation energies between 33 and 65 MeV. The γ-ray yield from the decay of giant dipole resonances built on excited states is found to be suppressed, implying that isospin mixing is small. By comparison with data from the literature at lower excitation energy, we conclude that isospin is a better symmetry in these compound nuclei at high excitation energy.

• Received 30 November 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.3201