Investigation of fine structure in the photoneutron cross sections of 16O and 208Pb

The structure in the photoneutron cross sections of 16O and 208Pb has been studied by the measurement of high resolution photoneutron energy spectra using the neutron time-of-flight technique and bremsstrahlung irradiations. For 16O, the ground state differential cross section at 98 degrees has been deduced between 17.3 and 28.5 MeV and is in good agreement with most previous studies. Fine structure is seen throughout the cross section. Eight neutron energy spectra for 208Pb from bremsstrahlung endpoint energies in the range 11.0 to 15.5 MeV were obtained. Strong peaks are seen at center of mass neutron energies of 1.67, 1.85, 2.06, 2.19, 2.68, 3.15, 3.27, 3.50, 3.77, and 4.03 MeV with weaker peaks elsewhere. The energies of these peaks are in good agreement with previous measurements in this laboratory. The energies of peaks in the spectra are compared with recent cross section measurements. (Author)