Methods Based on the Absorption of Gamma-Ray Beams by Matter

Abstract

Physical effects of a gamma-ray beam passing through matter as a basis for soil density determination is discussed. These effects for moderate-energy gamma rays are the photoelectric and Compton effects and production of electron-positron pairs in the electric field of the nuclei. In order to justify this general statement the narrow and broad gamma-ray beams were experimentally analysed. It is shown that for light elements and intermediate-energy of gamma rays the mass absorption coefficient μ is independent from the atomic number and consequently on the chemical composition of the material. This effect creates the physical basis for use of gamma-ray absorption for measuring the density of multi-component media like rock and soil material. The mass absorption coefficient for gamma-rays is an important parameter for absorbing media, governing the sensitivity of the gamma-ray absorption method, the degree to which such measurements represent the medium as a whole and the reliability of density measurements. Studies of moisture dynamics in soils and other ground materials, evaporation processes and also determination of the amount of water stored in the snow cover by the gamma-ray absorption method are discussed in this chapter.