Bremsstrahlung photons as a probe of hot nuclei

Aside from the dominant production of hard photons in first-chance p-n collisions, a significant hard-photon production in a later stage of heavy-ion reactions is predicted by the BUU theory. These thermal hard photons are emitted from a nearly thermalized source and still originate from bremsstrahlung produced in individual p-n collisions. The calculations predict that the production of the thermal hard photons is strongly correlated with the incompressibility of nuclear matter. Tentative experimental evidence for their production is found in the hard-photon energy spectra measured in the systems 86 Kr + nat Ni at 60.0 A MeV, 181 Ta+ 197 Au at 39.5 MeV and 208 Pb+ 197 Au at 29.5 A MeV.