Photoneutron cross section measurements on ^208Pb in the Giant Dipole Resonance region

Photoneutron reactions on ^208Pb in the Giant Dipole Resonance energy region have been investigated at the γ-ray beam line of the NewSUBARU facility in Japan. The measurements made use of quasi-monochromatic laser Compton backscattering γ-ray beams in a broad energy range, from the neutron threshold up to 38 MeV, and of a flat-efficiency moderated ^3He neutron detection system along with associated neutron-multiplicity sorting methods. We report absolute cross sections and mean photoneutron energies for the ^208Pb(γ, inX) reactions with i = 1 to 4. The fine structure present in the ^208Pb(γ, n) cross sections at incident energies lower than 13 MeV has been observed. The photoabsorption cross section has been obtained as the sum of the (γ, inX) reaction cross sections. By reproducing the measured ring-ratio values at excitation energies below the two neutron separation energy, we were able to extract estimations on the ^208Pb(γ, n) photoneutron energy spectra and on the partial photoneutron cross sections for leaving the residual ^207Pb in its ground and first two excited states. The present results are compared with data from the literature and statistical model calculations.