In the Electron Probe Microanalysis, the effect of grain size in multi-phase systems on the observed X-ray intensities was taken into account, and some experiments were carried out by the use of the ARL-type EPMA.
Theoretical calculation, although a rough one, revealed that the X-ray intensities are greatly affected by the presence of grain or the granularization of elements whose mass absorption coefficient ü or density ρ is considerably from that of the matrix, even if the grain-size is much smaller than the spot-size of the electron beam. For example, Si-Kα intensity from Al-12wt%Si alloy, having precipitated Si particles of the grain-size of 1ü or less (the same order or less compared to the smallest electron beam size or the X-ray emitting area), is about 10% higher than that expected from Birk's formula under the assumption that the specimen is uniform and of the same chemical composition. Experimental results showed rather good agr-eement with theoretical values.