Sensitivity of in-situ γ-ray spectra to soil density and water content

The effects of sediment water content and bulk density on measurements of in-situ environmental γ-radiation were investigated using Monte-Carlo simulations. The simulations consider a large bismuth–germanate detector in a semi-infinite geometry. The volume contributing radiation to the detector decreases with increasing sediment bulk density, as the detector ‘sees’ a constant sediment mass. The effect of variations in porosity on γ-ray spectra is negligible. Variations in water content affect the shape of the spectra only in the region below 0.1 MeV and, more importantly, strongly affect spectral intensity. Separate measurements of sediment water content, when expressed as mass fraction of water, can be used to correct spectra collected on sediments with varying water content.