X-and gamma-ray attenuation metering for environmental pollution control

Abstract

Density metering instruments, based on the attenuation of gamma-rays, are used for non-intrusive monitoring of fluids, solids and gases. Applications include thickness gauging, fluid level indicators and determining the composition of two phase systems. This paper describes a study to investigate how the technology can be developed for environmental monitoring and control. Environmental pollutants, Zn and Pb, were selected for the initial study. A 3.7 GBq²⁴¹ Am source was used to measure the sensitivity of the technique at 17, 20, 26 and 59.5 keV with a Ge planar semiconductor detector for optimum resolution of the photon energies. The optimum thickness for measurements using these four energies was 4 cm. The equipment was calibrated with a 2000 mg/l solution of zinc chloride and a 1000 mg/l solution of lead nitrate. A series of lower concentration solutions were measured to test the accuracy of the method, and demonstrated agreement with the actual concentrations within statistics. The sensitivity of the equipment was 100 mg/l for zinc and 50 mg/l for lead. The limitation to accuracy and precision was the stability of the counting equipment and theoretical detection limits of around 20–50 mg/l should be achieved if the stability of the electronics is improved.