The effect of various soil parameters on the interpretation of neutron moisture meter measurements

A set of curves has been developed which relates thermal neutron flux distribution to soil moisture content over a wide range of soil densities and nuclear parameters. The curves, which pass through points calculated using a multi-group three-dimensional diffusion code, have been fitted to empirical formulae in which the coefficients and indices are functions of the soil parameters. This information is written into a simple computer code which uses the soil parameters and a moisture meter count rate to calculate the moisture content. Differentiation of the empirical formulae allows calculation of the errors introduced by lack of precision in each of the parameters. The model may be used either in the design of probes to determine, for example, the effects of the source/detector separation, different detector geometries and source materials or in place of calibration curves for different soils, provided that the soil parameters are known