Highlighting of the Local Neutronic Efficiency Distribution in the MEGAPIE Spallation Target by GEANT4 Modeling

This work aims to assess the local spallation efficiency in the MEGAPIE spallation target of the Paul Scherrer Institute in Switzerland. Such information is a real key to consider a material and/or geometrical optimization of this target. The study focused particularly on two physical quantities that reflect the local neutronic performance of the target. These are the local production rates of neutrons and secondary protons. The calculations are performed using the Monte Carlo method based on the GEANT4 toolkit. The obtained results showed that the neutron yield of the target presents clear singularities at same levels and not quite regular in the whole active zone. These are the real spallation centers which are in fact only two or three distinct layers. The spallation region is thus very short compared to the one known today. This localization makes possible a well focused material and/or geometrical promotion for a better performing target.