Photoneutron cross section forO16

The photoneutron cross section for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ has been measured with monoenergetic photons from 17 to 33 MeV. This measurement was carried out by subtracting the photoneutron yield for Si from that for Si${\mathrm{O}}_2$, thus reducing the uncertainty in the neutron detection efficiency associated with the neutron moderation by the hydrogen in a water sample. The present cross-section results agree with the mean of several previous measurements with monoenergetic photons, and resolve a prior discrepancy at the 22.1-MeV peak. The measured average photoneutron energy is quite large in the photon energy region from 26 to 28 MeV, signifying that ground-state transitions dominate the ($\gamma , n$) cross section there.