XRF intensity in the frame of the transport theory

Equilibrium radiative transfer techniques were used to study the XRF emission of a thick solid sample. The Boltzmann transport equation was used todescribe the diffusion of photons in an infinitely thick homogeneous specimen. An exact solution has recently been reported for photons emitted by a collimated monochromatic x‐ray source, which is valid for all kinds of interactions. This solution was evaluated with a pure photoelectric kernel to obtain the exact narrow‐beam expressions of the primary, secondary and tertiary XRF intensities. As formally shown, the theory may easily be extended to describe the XRF emission produced with a polychromatic source. The intensity equations are compared with those deduced previously by Sherman and Shiraiwa and Fujino. For the primary and secondary intensities, good agreement with both groups is found (but with some minor corrections, pointed out in the text). A Sbiraiwa and Fujino tertiary equivalent expression is deduced, but shorter and with better numerical behaviour for high excitation energies. Both the theoretical background to the transport theory and the simplicity of the assumptions of the narrow‐beam model are sufficient to state unequivocally the appropriate physical meaning of every parameter in the solution. The importance of taking into consideration the inter‐line effects in pure target is also revealed. Copyright © 1989 John Wiley & Sons, Ltd.