Polarised X-rays in XRF-analysis for improved in vivo detectability of cadmium in man

A technique is described for the in vivo XRF-analysis of cadmium in the kidney cortex of man using plane polarised photons for excitation. The polarised photons are produced by scattering the radiation from an X-ray tube (W anode, 150 kV, 15 mA) in a polymethylmethacrylate disc at a 90 deg angle. The beam paths (X-ray tube to scatterer, scatterer to sample, sample to detector) must represent three mutually orthogonal directions. The minimum detectable concentration for a counting time of 1800 s and a skin-kidney distance of 30 mm is 8 micrograms g-1. This is a factor of 2.5 lower than our earlier method with direct excitation using the 59.5 keV photons from 241Am. The energy imparted has also been lowered from 0.4 to 0.2 mJ. The cadmium concentration in the kidney cortex of six occupationally exposed persons varied between 15 and 170 micrograms g-1.