Absolute Measurements of X-Ray Beam Energy and Photoneutron Cross Sections for Natural Cu and Pb

Abstract

Absolute determination of X-ray beam energy by cavity ionization camber method has been described and absolute photoneutron cross sections for natural Cu and Pb have been determined with an ETL quantameter and a 4π neutron detector using the X-ray beam from a 25 MeV betatron.
Peak photoneutron cross section for natural Cu and Pb are 78±8 m at 17.2 MeV and 660±60 mb at 14.1 MeV, respectively. These values are about 20% lower than the average cross section value obtained by several bremsstrahlung experiments. σ₋₂ for Cu and Pb are 1.81 mb/MeV from threshold to 24 MeV and 18.6 mb/MeV from threshold to 23 MeV, respectively. Using the contribution of the (γ, p) cross section for Cu, the ratios of σ₋₂ to 0.00225 A^5⁄3 mb/MeV for Cu and Pb are 0.95±0.14 and 1.13±0.17, respectively.