A compact fast-neutron producing target for high resolution cross section measurements

A proper knowledge of neutron cross sections is very important for the operation safety of various nuclear facilities. Reducing uncertainties in the neutron cross sections can lead to an enhanced safety of present and future nuclear power systems. Accurate neutron cross sections also play a relevant role in many other disciplines such as astrophysics, medicine, and security. Therefore it is essential to have at disposal tools to measure the neutron cross sections at required resolution. The measurement accuracy required to extract properly resonance parameters of the cross sections can only be obtained at time-of-flight facilities specially designed to have a high resolution in energy. Among the other neutron TOF facilities available in the world, the bremsstrahlung-based Geel Electron LINear Accelerator (GELINA) facility of the Joint Research Centre of the European Commission in Belgium is the one with the best energy resolution. The main goal of this thesis was to investigate the possibilities to improve even further the capabilities of this neutron data measurement facility. The thesis describes a design study with the purpose to further enhance the quality of the GELINA facility by proposing a new neutron producing target. It is demonstrated that there is a potential for an improved target to allow GELINA users to measure neutron cross sections with even higher accuracy. Therefore an effort was made to optimize the size, shape, and material composition of such a target design in view of the optimal neutron source characteristics, while providing an adequate solution for target cooling. The final design consists of seven 3 x 3 cm2 U-Mo plates with well-defined thicknesses in the direction of the beam. A plate-by-plate optimization has been carried out in order to maximize the neutronics properties of the target, while keeping the maximum plate temperatures reasonably low. A tantalum cladding coats each U-Mo plate to provide the required containment of radioactive material, and to avoid the direct contact of the U-Mo alloy with the Hg coolant. Seven Hg channels located in between the plates cool the target.Applied Science