Hard photon intensity interferometry in heavy ion reactions

Intensity correlations between hard photons produced in heavy ion collisions have been measured for ${\mathit{E}}_{\ensuremath{\gamma}}$\ensuremath{\ge}25 MeV in the reaction $^{86}\mathrm{Kr}$${+}^{\mathrm{nat}}$Ni at 60A Mev bombarding energy. The observed correlation pattern is interpreted in terms of intensity interference. A correlation length of ${\mathit{C}}_{\mathrm{\ensuremath{\sigma}}}$=16\ifmmode\pm\else\textpm\fi{}4 MeV is found and the deduced photon source extent is discussed.