Coherent scattering and matrix correction in bone-leadmeasurements

Abstract

The technique of K-shell x-ray fluorescence of lead in bone has been used inmany studies of the health effects of lead. This paper addresses one aspect ofthe technique, namely the coherent conversion factor (CCF) which convertsbetween the matrix of the calibration standards and those of human bone. TheCCF is conventionally considered a constant but is a function of scatteringangle, energy and the elemental composition of the matrices. The aims of thisstudy were to quantify the effect on the CCF of several assumptions which maynot have been tested adequately and to compare the CCFs for plaster of Paris(the present matrix of calibration standards) and a synthetic apatite matrix.The CCF was calculated, using relativistic form factors, for publishedcompositions of bone, both assumed and assessed compositions of plaster, andthe synthetic apatite. The main findings of the study were, first, thatimpurities in plaster, lead in the plaster or bone matrices, coherent scatterfrom non-bone tissues and the individual subject's measurement geometry areall minor or negligible effects; and, second, that the synthetic apatitematrix is more representative of bone mineral than is plaster of Paris.