Background (γ,n) cross section inPb208

A series of experimental estimates of the nonresonant radiative neutron reaction cross section in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ have been reported recently. To date, the results from ($\gamma ,n$) studies have been inconsistent with measurements of neutron-induced reactions. In an effort to resolve this discrepancy, the shape of the 41-keV resonance in the reaction ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(\gamma ,n){}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ has been studied in detail by simultaneous measurements of the photoneutron spectra at 90 and 135°. A small asymmetry in the resonance shape implies the presence of a background cross section of ${1.3}_{-0.7\mathrm{}}^{+2.7\mathrm{}}$ mb. This value can be explained in terms of contributions from neighboring resonances plus a small direct-reaction component; there is no evidence for anomalous processes. The result is consistent with the most recent data from study of the reaction ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}(n,{\gamma }_0)$.