An enhanced sensitivity K-shell x-ray fluorescence technique for tibial lead determination.

A novel irradiation-detection geometry capable of enhancing sensitivity for the measurement of tibial lead content by K-shell x-ray fluorescence (XRF) is described. The high-count-rate system comprised a small-area high-specific-activity (0.147 GBq mm-2) 109Cd source and a large-area (nominally 20 cm2) uncollimated detector, forming an axially symmetric back-scattering arrangement. Precisions in the range +/- 4.9 to +/- 14.2 micrograms Pb (g bone mineral)-1 have been obtained in a study of a cohort of 63 controls and 73 workers industrially exposed to lead. These precisions are comparable with those obtained in results using earlier systems, but at reduced source activities (less than 50% of the activity of other systems) and with significant reduction in measurement time (some 30% less than the measurement times of other systems). Subsequent investigation of detector collimation resulted in a marginal improvement in energy resolution, but the restriction in detected photon fluence meant that there was an insignificant change in detection sensitivity. For the resistive feedback preamplifier used in this study a maximum energy rate of the order of 7000 MeV s-1 was found to limit measurement precisions significantly. Higher-count-rate detector systems offer a basis for obtaining mean precisions down to +/- 3 micrograms Pb (g bone mineral)-1 at one standard deviation.