Nuclear Laboratory Setup for Measuring the Soil Water Content in Engineering Physics Teaching Laboratories

Soil water content (θ) is a crucial soil parameter that is determined in many studies involving engineering, geology, and soil and environmental sciences. For instance, evaluating the soil strength, groundwater recharge, hydraulic conductivity, and soil aeration status depends on θ. The measurement of θ is fundamental for monitoring and controlling several soil processes. The gamma-ray attenuation (GRA) technique is a fast and non-destructive way of evaluating θ in soils with very contrasting compositions. Although, GRA is rarely explored in lab physics classes. The proposal of an experiment using a teaching GRA apparatus for measuring θ is presented. The experimental setup consisted of a 137Cs radioactive source, a Geiger-Müller detector, and a radiation counter. Soil samples with four distinct granulometric compositions were analyzed. Strong linear correlations were found between the transmitted gamma-ray photon intensity and θ (correlation coefficients varying from −0.95 to −0.98). The soil porosity, measured by the conventional and GRA methods, presented differences that varied from c. 7.8% to c. 18.2%. In addition, strong linear relationships (correlation coefficients from 0.90 to 0.98) were observed between the GRA and the traditional (gravimetric) method of θ measurement. It was verified that the teaching GRA apparatus is useful for measuring θ. In addition, the apparatus allows the introduction of some important aspects related to the study of modern physics for undergraduate students of many fields of knowledge.