Material content of binary physical mixtures as measured with a dual‐energy beam of γ rays

摘要

The content of water and soil in physical intermixture was measured simultaneously and nondestructively by the attenuation of a dual‐energy beam of γ rays. The beam, 1 mm by about 3 cm in cross section, was devised by placing a 280‐mCi source of 137Cs behind a 389‐mCi source of 241Am, with lead collimators suitably aligned in front of each source and the scintillation probe. The probe was connected in parallel to two‐separate amplifier‐analyzer‐scaler systems, one being set in the integral mode to receive all pulses greater than 550 keV (for 137Cs, 662‐keV peak), with the other being set in the differential mode to receive all pulses in a band 35–85 keV (for 241Am, 60‐keV peak). When related to the count intensity in the high‐energy range, the count intensity e caused by 137Cs in the low‐energy band was empirically found to be independent of the material in the binary mixture (soil and/or water) placed in the beam for measurement. Also, e could be well expressed by a cubic polynomial that was then used along with a dead‐time correction to determine the attenuated count intensity attributable to the 241Am source alone. Calibration of the system was then possible. Over‐all measuring accuracy was on the order of ±0.01 cm3/cm3 in water content and ±0.02 g/cm3 in soil content (bulk density) for a counting period of 5 min; these changed to ±0.04 cm3/cm3 or g/cm3 for a counting period of 5 sec.