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Coincidence and Interference Corrections for Dual-Energy Gamma Ray Measurements of Soil Density and Water Content¹

ABSTRACT

Coincidence and interference errors in the dual-energy gamma ray attenuation method are discussed for simultaneous determination of water content and bulk density of soil columns. Collimated radiation from 300 mCi each of ²⁴¹Am and ¹³⁷Cs provides a high intensity beam comprised of 60 and 662 keV photons. Count rates measured by a single detector and a two-channel gamma spectrometer were corrected for coincidence losses due to pulse-resolving time. The lower energy channel counts were also corrected for Compton scattering of Cs radiation and for a counting loss attributable to a special coincidence interference.

Mass attenuation coefficients were determined for glass beads, water, and eight soil materials. Errors in soil water content measurement by the dual-energy gamma attenuation method appears to be restricted to standard deviations of approximately 1% due to practical limitations in measurement precision of 60 and 662 keV attenuation coefficients for soil and water.

¹ Contribution from the Soil-Water-Atmosphere-Plant (SWAP) Project in cooperation with the Southern Branch, SWCR, ARS, USDA. Florida Agr. Exp. Sta., Gainesville. Journal Series no. 4734. Research supported in part by CSRS.

² Assistant Professor of Soil Physics, Soil Science Dep.; Professor of Soil Physics, Soil Science Dep.; and Graduate Student, Dep. of Physics, respectively, Univ. of Florida, Gainesville 32601.

Received for publication December 8, 1972. Accepted for publication March 28, 1973.