The error introduced into a water density measurement due to the presence of a water density gradient.

Abstract

A multigroup diffusion code has been used to calculate the thermal neutron flux resulting from a neutron source in a homogeneous soil system in which there is a linear water density gradient. A relative neutron count rate is obtained by integrating the thermal flux over the volumes of different detectors in that flux. By repeating the calculation in the same soil system containing water at a constant density equal to that pertaining to the measuring point in the gradient system the change in flux due to the gradient can be determined. The magnitude of the effect is mainly a function of the soil density the slope of the water density gradient the proximity of the gradient to the detector and the water density. The mass absorption coefficient and the mass scattering coefficient have very little influence on this effect.