Abstract
An experimental method for the determination of mass absorption coefficients for the very soft X-ray region by use of EPMA and a composite target, prepared by evaporating a film of metal of different atomic numbers over a base layer, has been devised. In the method it is necessary to know the “equivalent thickness”, i.e. the thickness of the surface film, which satisfies the assumption that the characteristic X-ray intensities from backing materials in the composite targets under the surface films are equal to each other. A method of calculation for the “equivalent thickness” is proposed in this work.
The “equivalent thickness” is calculated with the aids of Cosslett and Thomass’ expression for the energy distribution of incident electrons in a solid target, and equations for the total electron transmission, for the backscattering coefficients of an isolated film and a massive target, and for the mean energy of electrons transmitted through and backscattered from the isolated film and massive target. The values for the “equivalent thickness” of all elements from Z=12 to Z=92 are computed by use of these equations.
