Investigation of impact of soil texture, depth and gamma ray energy on the mass attenuation coefficient and determination of soil bulk density using Gamma-Ray Spectrometry

Abstract

The determination of the gamma-ray attenuation coefficient is a critical parameter in the characterization of the extent and diffusion of gamma radiation within intricate materials, such as soil. Soils exhibit a complex and diverse composition, characterized by the presence of several phases, including minerals, gasses, organic matter, water, and metals. The study demonstrates the utilization of gamma-ray spectrometry to determine the mass attenuation coefficient and soil bulk density. The impact of incident gamma-ray energy, soil texture, and soil depth on the mass attenuation coefficient is also investigated. The experimental measurements were conducted utilizing a gamma spectrometer equipped with a 2″ × 2″ NaI(Tl) detector at gamma energies of 0.356, 0.662, and 1.332 MeV using 133Ba, 137Cs, and 60Co sources, respectively. The soil samples corresponding to two textures and three depths were collected from the research farms of the Department of Soil Science, Punjab Agricultural University, Ludhiana. The study revealed that the attenuation coefficient depends on the energy of incident radiation and the nature as well as the composition of the soil. The mass attenuation coefficient was observed to decrease rapidly with the increase in gamma radiation energy. Mass attenuation coefficient was found to be higher for sandy loam compared to sandy clay loam textured soil. Moreover, the attenuation coefficient was higher for the lower depths than the upper depth. The comparison between the experimental and predicted values of the mass attenuation coefficient, utilizing the XCOM-NIST framework, demonstrated a satisfactory level of concordance within a 10% margin for gamma energies measuring 0.356 and 0.662 MeV. However, the agreement was slightly less favorable, with discrepancies of less than 12% for sandy clay loam samples and less than 15% for sandy loam textured soil samples, when examining a higher gamma energy of 1.332 MeV. The measured value of mass attenuation coefficient was used to calculate soil bulk density, which agreed reasonably well with the values obtained with the conventional method. Specifically, the sandy clay loam samples displayed a range of 7–14% deviation, while the sandy loam textured soil samples exhibited a range of 14–23% deviation. The investigation can be expanded to ascertain significant soil properties, such as porosity and moisture content.