Determination of a Time Scale for the Emission of High-Energy Photons in Heavy-Ion Fusion Reactions

Charged-particle-$\gamma$-ray coincidences have been measured following the fusion of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=60\mathrm{}$ MeV. Particle energy and angular distributions in coincidence with $\gamma$ rays detected with the Max Planck Institut-Gesellschaft für Schwerionenforschung $4\pi$ $\gamma$-ray spectrometer are measured, from which it is possible to estimate the time at which high-energy photons are emitted in the compound-nuclear decay process. In addition, information is obtained about the $\gamma$-ray multiplicity associated with the energetic photons.