Spacial Distribution of Photoneutrons in an Iron Slab Produced by 20-MeV Electron Bombardment

Abstract

Photoneutron distribution was measured with activation of aluminum and magnesium in an iron slab bombarded by a beam of 20-MeV electrons from a linear accelerator. In order to compare with the experimental results, the spacial neutron distribution was calculated as follows : the photoneutron source distribution originating from the photonuclear reaction was calculated by an approximate analytical method ; and the neutron distribution in the medium was calculated on the basis of this distributed source by Monte Carlo code, CYGNUS. The calculated neutron distribution was in good agreement with the measured distribution, using activities of aluminum detectors. From the comparison of both saturated activities of aluminum and magnesium, it is found that the photonuclear effects are remarkable when γ is equal to 10 cm and Z is between 2 and 5 cm. The spacial distribution of neutron flux above about 6.5 MeV in the iron slab is nearly spherical symmetric around the beam incident point ; and an exponential attenuation with the slope of effective removal cross section of iron, ∑ₑffᴿ＝0.172 cm⁻¹.