Abstract
This paper presents an empirical method by Kang et al. recently proposed for correcting two-dimensional neutron radiography for water quantification in soil. The method was tested on data from neutron imaging of the water infiltration in a soil sample. The raw data were affected by neutron scattering and by beam hardening artefacts. Two strategies for identifying the correction parameters are proposed in this paper. The method has been further developed for the case of three-dimensional neutron tomography. In a related experiment, neutron imaging is used to record ponded-infiltration experiments in two artificial soil samples. Radiograms, i.e., two-dimensional projections of the sample, were acquired during infiltration. A calculation was made of the amount of water and its distribution within the radiograms, in the form of two-dimensional water thickness maps. Tomograms were reconstructed from the corrected and uncorrected water thickness maps to obtain the 3D spatial distribution of the water content within the sample. Without the correction, the beam hardening and the scattering effects overestimated the water content values close to the perimeter of the sample, and at the same time underestimated the values close to the centre of the sample. The total water content of the entire sample was the same in both cases. The empirical correction method presented in this study is a relatively accurate, rapid and simple way to obtain the quantitatively determined water content from two-dimensional and three-dimensional neutron images. However, an independent method for measuring the total water volume in the sample is needed in order to identify the correction parameters.
Highlights
Neutron imaging (NI) is a modern non-destructive, non-invasive material structure visualization technique
A non-linear method was used, where the value of coefficient β was fixed at a value of 0.105 cm−2, while parameter Σ was optimized by the least squares method in order to minimize the difference between the actual water volume in the sample and the neutron derived water volume
Two ponded-infiltration experiments were monitored by the neutron imaging method
Summary
Neutron imaging (NI) is a modern non-destructive, non-invasive material structure visualization technique. The water content profile of the ceramic in Slice 1 (Figure 4a) was significantly biased without correction, ranging from 0.32 to 0.43, while after correction it was almost constant at a value of 0.37. The radial water content profile for the sand layer (Figure 4b) shows that the correction did not affect the water content close to the centre of rotation. This paper has presented our work on a correction method that removes the bias of the water content distribution within the sample, rather than the total bias of the water content
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