Comparison between depleted uranium and lead shadow shields in neutron-induced prompt gamma-ray analysis

The effective use of neutron induced prompt γ-ray analysis depends on a detailed understanding of neutron interactions. A theoretical examination of nuclear data for various shield materials in this technique has shown that tungsten and uranium provide the best direct shielding over a wide range of neutron energies. A 15 cm thick shield of these materials reduces the primary fast neutrons from the 252Cf source by a factor of up to 500. Lead, on the other hand, has the advantage of a large thermal neutron scattering cross-section. A comparison of these theoretical results with experiment, using depleted uranium and lead, has shown that neutron scattering from the sample and surroundings is a major source of the fast neutrons incident on the detector. The experimental results indicate that a uranium-lead shadow shield provides a good combination for the reduction of the direct fast neutron component. (author)