Patent ID: 7529337

Claim:
A method of measuring an amount of an element contained in a sample based on a fluorescent x-ray excited out from the sample by an irradiation of a primary x-ray, the method comprising: providing a base function defining a lower detection level of measurement in relation to a sensitivity of the measurement and a background intensity of the fluorescent x-ray, wherein the background intensity is a function of a first background intensity effected by a pileup and a second background intensity effected by other causes; sequentially irradiating a first and second primary x-rays onto the sample and detecting the respective fluorescent x-rays excited out from the sample by the first and second primary x-rays; calculating the first background intensity and the second background intensity based on a difference in intensity between the first and second primary x-rays; calculating the sensitivity, based on a spectrum of the fluorescent x-ray excited out by the first primary x-ray; calculating an effective sensitivity and an effective background intensity to be exhibited with the primary x-ray irradiated at an optimum intensity, wherein the effective sensitivity is a function of the calculated sensitivity and an intensity ratio between the optimum intensity and the intensity of the first primary x-ray, and the effective background intensity is a function of the calculated first and second background intensities and the intensity ratio; using the effective sensitivity and the effective background intensity, solving the base function to derive the intensity ratio which minimizes the lower detection level; and irradiating the primary x-ray onto the sample at the optimum intensity determined from the calculated intensity ratio.