Assessment of soil bulk density using gamma ray spectroscopy

This study deals with a method nuclear technique method utilizing Gamma Ray Spectroscopy for the assessment of material bulk densities, specially soil density. The spectroscopy system consists of; 3” × 3” inch scintillation NaI(Tl) detector connected to multichannel analyzer Inspector 2000 from Canberra instruments and a laptop computer, 137Cs radiation source and four different bulk materials with known densities. To calibrate the spectrometric system, detector and radiation source were placed in direct contact with the surface of the bulk materials located in wood boxes manufacture for this purpose. The distance between the radiation source and the detector varies from 10 cm to 30 cm. The Radiation source was shielded so that the emitted photons from the source travel in direction perpendicular to the top surface of the bulk material, and therefore the detector will register photons interacting with the material and scattered towards it. A relation was established between the density of the materials used for calibration and the count rate in different parts of the gamma ray spectrum, the full energy peak, the region of expected backscattering peak (from 50 Kev to 250 Kev), and the region containing Compton’s continuum and the full energy peak as well. Actual field measurements on Terra Rosa soils showed that, the best results of bulk density evaluation were obtained when the detector and the radiation source are separated by 20 cm distance. Based on which parts of the spectrum are used for data analysis, the differences in bulk densities measured in the field and real values varies between 0.5% and 6%