Photonucleon Total Cross Sections at Very High Energy

Photon-neutron total cross sections have been evaluated from the data for the proton and deuteron presented in the preceding paper. Simple Regge-pole fits have been made to σT(γp) and σT(γn), both of which extrapolate to 94 ±{} 4 {μ}b at infinite energy. Over the range of our data, 3.7 to 17.9 GeV, σT(γn)<σT(γp), which can be interpreted to give a ratio of exchange contributions, A₂P^'=0.19±0.04. A fit to σT(γp) is also important for predictions of the proton cosmic-ray spectrum.