PHOTON-INDUCED NUCLEAR REACTIONS ABOVE 1 GeV. III. FISSION IN GOLD AND LEAD.

Abstract The photofission cross section per equivalent quantum and the forward-to-backward ratios of gold and lead have been measured in the bremsstrahlung energy range 1.0–7.4 GeV using glass detectors. The experimental data are analysed using data from an earlier lower-energy experiment done at Lund with the same experimental technique. It is verified that the fission cross sections for the two target elements are almost constant above 1 GeV. From the moderate dependence of the forward-to-backward ratio on photon energy it is concluded that the excitation energy of the fissioning nucleus and the momentum transferred to it are rather independent of photon energy. The forward momentum deposited at the instant of fission is shown to increase only slowly, decreasing from 40 % to 10 % of the compound-nucleus value in the energy interval studied.