Photoneutron cross section measurements on Pb208 in the giant dipole resonance region

Photoneutron reactions on ^208Pb in the giant dipole resonance energy region have been investigated at the -ray beam line of the NewSUBARU facility in Japan. The measurements made use of quasimonochromatic laser Compton backscattering -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 (, 0. 16em{0ex}inX) reactions with i=1 to 4. The fine structure present in the ^208Pb (, 0. 16em{0ex}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 (, 0. 16em{0ex}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 (, 0. 16em{0ex}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.