INFLUENCE OF PHYSICAL AND CHEMICAL PROPERTIES OF SOIL ON MEASUREMENTS OF WATER CONTENT USING NEUTRON PROBES

The multigroup transport theory was used to study the influence of the physical and chemical properties of soil on the measurement of the water content by means of neutron probes. Calculations of the thermal neutron flux were made to examine the behavior of four soils (two of which are really rocks) frequently encountered in Southern Italy: Siliceous sand, limestone, dolomitic limestone, and terra rossa. The results show that although these soils do not contain elements with a great capture cross section for thermal neutrons (boron, chlorine, cadmium, etc.) they behave in quite different ways in the process of neutron moderation, diffusion, and capture. Hence, the response of the probe varies considerably for the same water content and dry density. Interpretation of the values obtained is thus not reliable, and the measurement of the water content by thermal neutron counts does not provide a sufficient guarantee of accuracy. © 1968 by the Chinese Geophysical Society