A thorough theoretical study of the typical iron–nickel–chromium ternary system confirms the essential variability of influence coefficients with composition, thus accounting for the limited validity of empirical coefficient procedures. The origin and mechanisms of coefficient variation are accurately described, namely by distinguishing between binary or ‘longitudinal’ variation, it being related to either an enhancement effect or the use of polychromatic excitation or possibly both, and ‘transverse’ variations resulting from fluorescence crossed effects as well as tertiary fluorescence if represented. As a consequence a general mathematical expression, including all these effects and exactly matching the theoretical intensity equations, is assigned to the coefficients for the entire range of compositions. On a practical basis, precision considerations allow to simplify these relationships considerably and reduce them to a fairly simple, flexible system of ‘crossed’ influence coefficients. Since it closely conforms to the fundamental principles of fluorescent emission, this new scheme should prove effective for determining multicomponent systems, namely by allowing accurate analysis to be performed over a wide range of compositions ‘without standards’.
Combining the techniques by Feather and Willis on the one hand and Bougault et al. on the other allows the development of a simple, effective method for determining trace elements in rocks. Both the matrix correction factor and the true background level are deduced from the specimen scattering, i.e. the intensity of a Compton peak (or possibly an interference-free background), and then operated in a single Bougault type equation which gives the trace element concentration. The theoretical and experimental bases for this method are described, as well as a typical application to the determination of Ni, Zn, Rb, Sr, Zr and Nb in a series of standard rocks. L'association des techniques de Feather et Willis d'une part, Bougault et al. d'autre part permet de dkvelopper une mkthode simple et efficace de determination des klkments traces dans les roches. Le facteur de correction matricielle ainsi que le niveau du fond vrai sont deduits de la diffusion du specimen, mesurCe d'aprks I'intensitk d'un pic Compton (ou a dkfaut de celle d'un fond libre d'interfkrences), et introduits dans une Bquation unique du type Bougault qui dBlivre la concentration de 1'Blkment trace. On dCcrit les bases thkoriques et experimentales de cette methode, de meme qu'une application typique A la dktermination de Ni, Zn, Rb, Sr, Zr et Nb dans une skrie de roches Btalons.
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