Authors: Peter Vontobel, R. Hassanein, A. Carminati, A. Kaestner,P. Lehmann, A. Koliji.

Abstract
In soils, structures such as aggregates and fissures dominate the displacement of water, air and solids, because they cause spatially non-uniform non–equilibrium flow. We can improve our understanding of these flow processes by making use of the recent advances in the imaging techniques. Neutron imaging is used to visualize the heterogeneous structure of soil physics samples with various size and composition and to measure the transport of humidity in such materials. Neutron imaging, with a spatial resolution ranging from 0.05 – 0.3 mm, provides at the same time information on the macroscopic material heterogeneity and the water transport dynamics. This information is essential for the development and validation of simulation models. Due to the high scattering probability of hydrogen, a high sensitivity for small changes in humidity concentration is provided. However quantitative evaluations of neutron imaging results have to take into account the scattering contributions from the sample and the detector. We summarize several soil-physics experiments measured at the spallation neutron source SINQ. The choice of sample size and composition and the quantitative evaluation of experiments will be explained.

Authors Description
Peter Vontobel has a mechanical engineering degree from ETH in Zurich. At the beginning of his professional career he was working in the field of nuclear engineering and reactor physics. In the 1990’s he focused his research interest on positron emission tomography. Since 1998 he deals with neutron radiography and tomography at the spallation neutron source SINQ of the Paul Scherrer Institute, Villigen, Switzerland.