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

Photoneutron reactions on $^{208}\mathrm{Pb}$ in the giant dipole resonance energy region have been investigated at the $\ensuremath{\gamma}$-ray beam line of the NewSUBARU facility in Japan. The measurements made use of quasimonochromatic laser Compton backscattering $\ensuremath{\gamma}$-ray beams in a broad energy range, from the neutron threshold up to 38 MeV, and of a flat-efficiency moderated $^{3}\mathrm{He}$ neutron detection system along with associated neutron-multiplicity sorting methods. We report absolute cross sections and mean photoneutron energies for the $^{208}\mathrm{Pb}(\ensuremath{\gamma},\phantom{\rule{0.16em}{0ex}}inX)$ reactions with $i=1$ to 4. The fine structure present in the $^{208}\mathrm{Pb}(\ensuremath{\gamma},\phantom{\rule{0.16em}{0ex}}n)$ cross sections at incident energies lower than 13 MeV has been observed. The photoabsorption cross section has been obtained as the sum of the $(\ensuremath{\gamma},\phantom{\rule{0.16em}{0ex}}inX)$ 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 $^{208}\mathrm{Pb}(\ensuremath{\gamma},\phantom{\rule{0.16em}{0ex}}n)$ photoneutron energy spectra and on the partial photoneutron cross sections for leaving the residual $^{207}\mathrm{Pb}$ in its ground and first two excited states. The present results are compared with data from the literature and statistical model calculations.