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.
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