Methods of scattering corrections for quantitative neutron radiography

Abstract

From neutron radiography experiments, often statements like “how many grams of water are in my sample?” are expected. Such statements are delicate, because contributions of scattered neutrons in the image signal disturb the radiographies for a simple quantitative evaluation. The idea is to consider the scattered neutrons in a computational procedure. The obtained corrected image data set can then be evaluated according to the exponential attenuation law or reference values obtained by simulations or experiments. The correction is based on the iterative reconstruction of the measured image by overlapping point scattered functions (PScF). The PScFs are determined by Monte-Carlo simulations using the MCNPX software. Important parameters beside the material are the dimensions of the sample, the distance between sample and detector, the detector properties and the energy spectrum of the initial neutron beam. Evaluations of measurements with different detectors result in differing effective attenuation cross-sections of the samples. This can be explained by the different detector sensitivity on the epithermic domain of the energy spectrum. If the sample is inside an enclosing material (e.g. water in a container), this can affect the evaluation of the samples cross-section. Also this effect is understood with the PScF and can be taken into account. For known simple geometries the reconstructions are in good agreement with the measurements and allow a more exact evaluation of the involved cross-sections.