Soil water retention curve determined by gamma-ray beam attenuation

The soil water retention curve relates the soil water matric potential (ψm) and the soil water content (θ). When no significant changes occur in soil structure, the water retention curve can be considered as a soil physical characteristic. This article presents a new procedure for soil water retention curve evaluation using gamma-ray beam attenuation as an auxiliary technique for θ determination. The radioactive source used in the experiment was 241Am, and the detector was a 3″ × 3″ NaI(Tl) scintillation crystal coupled to a photomultiplier tube. The proposed procedure avoids the need of frequent sample manipulation as in the case of the conventional method. The water content can be continuously monitored inside the chamber allowing a more precise judgment of the equilibrium. The time required for the retention curve determination can be significantly reduced in comparison with the traditional method. Therefore, the new procedure presents many advantages in relation to the traditional method and in that it can be routinely used for soil water retention curve determination.