A study of the formation of compound nucleus states by absorption of 30 to 90 MeV photons in Sn, Ce, Ta and Pb nuclei

From measurements sigmasup((i)) (Esub(γ)) = Σsub(i=j)sup(isub(max)) sigma(γ, in...) on four heavy nuclei (Sn, Ce, Ta, Pb) from 30 to 90 MeV with monochromatic photons one obtains the cross section for the formation of a compound nucleus state excited with the full energy of the absorbed photon. This cross section is compared with high energy extrapolation of the Lorentz line which fits sigma(tot): Esub(γ)) on the giant dipole resonance and with the absorption on a quasideuteron pair. A value 3.5 fm < lambda < 8.5 fm is deduced for the mean free path of a fast nucleon in these heavy nuclei. (orig.)