Angular Distributions of Fast Photoneutrons from Pb, Bi and Ta

Abstract

Using a stilbene scintillation detector, the angular distributions of fast photoneutrons of energies greater than two bias values of 7.4 MeV and 8.7 MeV were measured for Pb, Bi and Ta at 25.5 MeV end point energy of the bremsstrahlung. For Pb and Bi, the angular distributions were found to be asymmetric about 90 degrees with respect to the gamma-ray beam axis and were strongly peaked in a forward direction, but in the case of Ta not so obviously. The angular distributions were fitted to W(θ)=A+Bsin 2 θ+Ccos θ, using a least squares analysis. The present experiment indicates that, in the high energy region of the (γ, n) spectrum, C/A increases with the detecting threshold energy for neutrons and on the otherwise B/A decreases with the energy.