Photoneutron spectrum of lead following excitation by 8999, 8533, and 8120 keV photons

The photoneutron spectrum of natural lead has been observed for photoexcitation energies of 8999, 8533, and 8120 keV using a high-resolution ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ ionization chamber. The photons were obtained from the ($n,\gamma$) reaction on a nickel target positioned in a nuclear reactor. The $Q$ values for the three reactions ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(\gamma ,n){}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$, ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}(\gamma ,n){}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$, and ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}(\gamma ,n){}_{}{}^{205}{}_{}{}^{}\mathrm{Pb}$ have been determined and are, respectively, 7369 ± 5, 6743 ± 3, and 8087 ± 3 keV. Neutron groups corresponding to different final states following excitation by one of the three photon components have been observed and their partial cross sections are reported. The distribution and some systematics of the neutron reduced widths have been studied. The absolute cross sections of the reaction ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(\gamma ,n){}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ at 8999 and 8533 keV photon energies have been found to be 6.8 ± 2.9 and 5.0 ± 2.1 mb, respectively.