Hard photons in heavy-ion collisions: Direct or statistical?

Photons with energies from 2 to 60 MeV have been measured in coincidence with binary fragments in the reaction ${}_{}{}^{92}{}_{}{}^{}$Mo${+}^{92}$Mo at an incident energy of 19.5A MeV. The rapid change of the γ-ray spectrum and multiplicity with the fragment total kinetic energy in the exit channel indicates that the γ rays are emitted statistically by the highly excited fragments. Temperatures as high as 6 MeV are inferred.