A Spatial Resolution and Vacuum Channeling Phenomenon of the Neutron Transmission through Protection Screen

Frequently, shields used for protection against radiation contain some vacuum channels for passing cables and instruments for measurements. The neutron transmission through these shields is an unavoidable phenomenon, so we have interested in this work to study and discuss the effect of vacuum channels on neutron transmission through shields [1]. We have considered aninfinite homogenous slab, with a fixed thickness, which contains a vacuum channels, and an infinite plane source of neutrons which arrived on the left side of the slab and on the right side many detectors with fixed windows are placed to detect transmitted neutrons and evaluate the neutron transmission probabilities[2]. We used the simulation Monte Carlo method for sampling the neutron history in the slab [3;4] with a spatial biasing technique in order to accelerate the calculation convergence[5;6].Then different geometries of the vacuum channel have been studied. For each geometry and for several values of the channel opening we have determined the detector response and calculated the neutron transmission probability for different detector positions. This probability presents a peak for the detector placed in front of the vacuum channel. This study allowed us to clearly identify the neutron channeling phenomenon and to determine the optimal conditions of vacuum geometries to improve protection against neutron. In particular in the second part we considered a vacuum channel with two horizontal parts [7;8]. The spatial distribution of neutrons transmitted through the protection screen was determined and shows two peaks.This study allowed us to determine the smallest distance between the two horizontal parts for which the two peak scan be resolved. One application of our study is to detect vacuum defects in materials.