The theoretical formulas of the fluorescent x-ray intensity (the primary, the secondary and the tertiary fluorescent x-rays) are obtained and actual calculations are made for nickel-iron, iron-chromium, and nickel-iron-chromium alloys. In the calculation, the continuous intensity distribution of the irradiating x-rays for the wavelength is taken into account. The theoretical results agree with the experiments very well, the deviations being 1% at most, and it is concluded that the theoretical estimation of the fluorescent x-ray intensity emitted from samples of various composition is possible. The matrix effect, absorption effect, and enhancement effect are evaluated from the present theory. In the enhancement effect, secondary fluorescent x-rays are quite significant (for instance, the chromium secondary fluorescent x-rays from Cr 2% and Fe 98% alloy reach the 55% of the chromium primary fluorescent x-rays and they can not be neglected), but the tertiary fluorescent x-rays are only a few per cent. The usual approximation methods, where the irradiating x-rays are assumed as monochromatic rays and the secondary fluorescent rays are not taken into consideration are also discussed and their meaning is made clear.
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