Nuclear states in ${}^{28}\mathrm{Si}$ were populated at an initial excitation energy $E^{*}=50\mathrm{}$ MeV via the isospin $T=0\mathrm{}$ reaction ${}^{16}\mathrm{O}{+}^{12}\mathrm{C}$. The dilepton- and photon-decay yields were measured simultaneously for the first time up to transition energies of 30 MeV. Statistical decay calculations describe well both measurements on an absolute scale. The measured absolute dilepton cross section, integrated over the transition energy region 15–30 MeV, amounts to $\sigma \left(e^{+}{e}^{-}\right)=84\mathrm{}\pm 6$ nb. Implications for measuring a possible monopole strength are discussed.

• Received 27 October 1994

DOI:https://doi.org/10.1103/PhysRevLett.75.798