[Non-invasive determination of bone lead in human body using X-ray fluorescence excited by 109Cd]

A measurement system of X-ray fluorescence excited by 109Cd was set up for the in vivo measurement of bone lead. In the system, a HPGe detector (phi 10 mm x 7 mm) was used to detect the characteristic K X-rays of lead in tibia excited by gamma rays of 88.0 keV from 109Cd. By the normalization of lead X-rays to the coherent scatter, the content of bone lead was calculated from the calibration curves of the ratio (X-ray intensity: coherent intensity) against the lead concentration in tibia phantoms. The normalization technique rendered the measurement accuracy independent of tissue overlay thickness, bone shape, size, mass, and subject motion. Calibration curves obtained from a set of tibia phantoms with lead-doped plaster of Paris were linear. The results of pilot measurements showed that the contents of bone lead in the occupationally exposed workers were higher than those in the control group.