X-ray fluorescence analyzer

Abstract

By taking into account the geometric factors of the optical system in X-ray fluorescence analysis, the analysis of samples is performed at high speed. [Solution] The X-ray fluorescence analyzer 10 comprises an X-ray source 1 that irradiates a sample 3 with primary X-rays 2, a detector 5 (measuring means) that determines the measured intensity of secondary X-rays 4, a control unit 6 (theoretical intensity calculation means) that calculates the theoretical intensity of secondary X-rays 4 based on an assumed composition, and a control unit 6 (calculation means) that calculates the composition by successively approximate and correcting the assumed composition so that the measured intensity and the theoretical intensity match. The control unit 6 calculates the theoretical intensity by multiplying it by the detection efficiency of X-ray fluorescence corresponding to the sample depth from the surface of the sample 3 irradiated with primary X-rays 2 to the point inside the sample 3 where secondary X-rays 4 are emitted.

Description

[Technical Field]

[0001] This invention relates to an X-ray fluorescence analyzer that analyzes the composition and area density of a sample using the fundamental parameter method (FP method). [Background technology]

[0002] To determine the elemental composition in a sample, the fission product (FP) method is known, which compares the theoretical intensity of secondary X-rays calculated based on assumed elemental composition with the measured intensity to converge the assumed composition. The theoretical intensity can be calculated, for example, using the size of the sample and the intensity and incident angle of primary X-rays irradiated at various positions on the sample surface as parameters. In some cases, the theoretical intensity can be obtained by simulating the theoretical intensity of secondary X-rays for each optical path to take into account the geometrical factors of the optical system (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2006-292399 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The simulations required to determine the theoretical intensity described above are performed repeatedly for each primary X-ray path and to converge the assumed composition. Therefore, conventional X-ray fluorescence analyzers require a long time for analysis.

[0005] This invention has been made in view of the above points, and aims to enable high-speed analysis of samples. [Means for solving the problem]

[0006] To achieve the above objectives, The present invention A fluorescence X-ray analyzer for analyzing a sample, An X-ray source that irradiates the sample with primary X-rays, A measurement means for determining the measured intensity by measuring the intensity of secondary X-rays generated from the above sample, A theoretical intensity calculation means for calculating the theoretical intensity of secondary X-rays generated from each element in the above sample based on the assumed composition, A calculation means for calculating the composition of the sample by successively and approximately correcting the assumed composition so that the measured intensity and the theoretical intensity match, Equipped with, The theoretical intensity calculation means described above is characterized in that the theoretical intensity is calculated by multiplying the detection efficiency of the fluorescent X-rays, which corresponds to the sample depth, which is the distance from the surface of the sample irradiated with primary X-rays to the point inside the sample where secondary X-rays are emitted, by the theoretical intensity.

[0007] This allows for fast, highly accurate theoretical strength analysis of samples without the need for Monte Carlo simulations. [Effects of the Invention]

[0008] This invention enables high-speed analysis of samples. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram illustrating the configuration of an X-ray fluorescence analyzer. [Figure 2] This is a flowchart showing an example of the analysis process. [Figure 3] This graph shows an example of the relationship between sample depth and detection efficiency. [Figure 4] This is an explanatory diagram showing an example of measurement during the preliminary preparation. [Modes for carrying out the invention]

[0010] (Schematic configuration of an X-ray fluorescence analyzer) Embodiments of the present invention will be described in detail below with reference to the drawings.

[0011] As shown in FIG. 1, the X-ray fluorescence analyzer 10 includes an X-ray source 1 such as an X-ray tube that irradiates a sample 3 with primary X-rays 2, and a detector 5 (measurement means) that measures the intensity of secondary X-rays 4 such as fluorescence X-rays and scattered rays generated from the sample 3 to obtain a measured intensity, and a control unit 6 (theoretical intensity calculation means, calculation means) that performs calculation processing and the like on the elemental composition in the sample 3. In this X-ray fluorescence analyzer 10, for example, the analysis of the sample 3 is performed as follows.

[0012] (Analysis operation: Preparation) First, as shown in FIG. 2, the following processing is performed as preparation.

[0013] (S1) The sample depth (sample height) z, which is the distance from the surface of the sample 3 irradiated with the primary X-rays 2 to the point where the secondary X-rays 4 inside the sample 3 are emitted, and the detection efficiency dΩ d (z) of the fluorescence X-rays, for example, the relationship shown in FIG. 3 is obtained. Specifically, the above relationship is obtained by simulation or actual measurement, which will be described later.

[0014] (S2) As an approximate expression according to the above relationship, for example, the exponential function shown in the following (Equation 1) and the polynomial shown in (Equation 2) are obtained. Here, Ω ∞ , Ω0, α0··· are adjustment coefficients.

[0015]

Equation

[0016]

Equation

[0017] The above preparation may be performed only once, for example, when the X-ray fluorescence analyzer 10 is introduced and used for the first time. That is, the above detection efficiency of the fluorescence X-rays may be obtained in advance and stored so as to be used for the analysis of a plurality of samples.

[0018] (Analysis operation: Quantitative calculation operation) The quantitative calculation process itself is the same as that of the standard FP method, but the calculations performed are carried out as follows, resulting in faster analysis.

[0019] (S3) First, the secondary X-ray intensity is measured for sample 3.

[0020] (S4) In addition, the composition of sample 3 is assumed, as in the usual FP method.

[0021] (S5) The theoretical intensity of secondary X-rays is calculated based on the assumed sample composition. Specifically, the following calculations are performed.

[0022] Here, generally speaking, the detection efficiency of fluorescent X-rays dΩ depends on the sample depth z. d The fluorescence X-ray intensity I when this is not considered can be expressed by the following equation (Equation 3). In equation (Equation 3), E is the energy of the incident X-ray, ρ is the density of the sample, t is the thickness of the sample, μ(E) is the X-ray physical parameter (mass absorption coefficient with respect to the energy of the incident X-ray), μ(Ei) is the X-ray physical parameter (mass absorption coefficient with respect to the energy of the generated fluorescence X-ray), ψ1 and ψ2 are the incident angle and escape angle of the X-ray for sample 3, respectively, I0(E) is the intensity of the incident X-ray (primary X-ray), Q i (E) is the fluorescence X-ray generation efficiency of the quantitative element.

[0023]

number

[0024] Here, the term dependent on the sample depth in (Equation 3) is denoted as g(E) as in (Equation 4).

[0025]

number

[0026] For this sample depth-dependent term g(E), in this embodiment, the detection efficiency dΩ is as shown below (Equation 5). d The corrected formula g(E)', which is multiplied by the given factor, is used.

[0027]

number

[0028] In this (equation 5), the sample depth z can be calculated using numerical integration methods such as the trapezoidal method or Simpson's method with an appropriate step size to obtain a highly accurate theoretical strength.

[0029] Furthermore, the dΩ in (Equation 5) above d However, when the integral is expressed as an exponential function of the sample depth z, as shown in (Equation 1) above, we can obtain equation g(E)' by solving the integral as shown in (Equation 6) below.

[0030]

number

[0031] Also, the dΩ in (Equation 5) above d However, when the integral is expressed as a polynomial of sample depth z, as in (Equation 2) above, we can obtain equation g(E)' by solving the integral as shown in (Equation 7) below.

[0032]

number

[0033] Here, I0, I1, and I2 in (Equation 7) above are (Equations 8) to (Equation 10) below.

[0034]

number

[0035]

number

[0036] [Number]

[0037] By obtaining the theoretical strength with the algebraic expression in which the integration is expanded in this way, compared with the case of performing a Monte Carlo simulation, it is possible to obtain a high-precision theoretical strength that is fast and takes into account the detection efficiency depending on the sample depth z.

[0038] (S6) The theoretical strength and the measured strength are compared, and the sample composition is sequentially corrected so as to match, and the steps after (S3) are repeated.

[0039] (Specific Example 1 of Preliminary Preparation) The sample depth z, which is the distance from the surface of the sample 3 to the point where the secondary X-ray 4 inside the sample 3 is emitted, as shown in FIG. 3, and the detection efficiency dΩ of the fluorescent X-ray d An example of obtaining the relationship with (z) by Monte Carlo simulation will be described.

[0040] Regarding the observable region where the irradiation region of the primary X-ray generated by the X-ray source 1 tube overlap with the detection region that can be observed by the detector 5 (where the secondary X-ray can enter the detector 5), for each plane of the sample depth z at a predetermined interval (step), using a random number, determine the position where the secondary X-ray is generated and the traveling direction. When the secondary X-ray enters the detection window of the detector 5 and can be observed, count it. Repeat the above-described position determination and counting a predetermined sufficient number of times, and calculate the total count. Also, repeat the above process step by step for each sample depth z.

[0041] Thereby, the relationship between the sample depth (sample height) and the detection efficiency (detector solid angle) as shown in FIG. 3 is obtained.

[0042] (Specific Example 2 of Preliminary Preparation) Sample depth z and detection efficiency dΩ of fluorescent X-ray dThe relationship with (z) may be determined by actual measurement. For example, as shown in Figure 4, a spacer 7 is placed between the target X-ray fluorescence analyzer 10 and the sample 3, and the distance between the X-ray fluorescence analyzer 10 and the surface of the sample 3 is varied by predetermined steps, and the intensity of the secondary X-rays incident on the detector 5 is measured for each sample depth z. Here, the sample 3 does not have to be the sample actually being analyzed, but it is preferable that it be an element with a large X-ray absorption coefficient, such as copper (Cu) or zinc (Zn), because it is easier to measure secondary X-rays mainly from the surface of the sample 3 (short analysis depth). In addition, it is necessary to select X-ray fluorescence with an energy at which absorption by air can be ignored.

[0043] Through such measurements, the relationship between sample depth (sample height) and detection efficiency (detector solid angle), as shown in Figure 3, can be determined.

[0044] The above simulation only needs to be performed once for the X-ray fluorescence analyzer 10, and does not need to be performed for each actual sample 3 analysis, thus easily enabling faster analysis. [Explanation of Symbols]

[0045] 1 X-ray source 2 Primary X-ray 3 Samples 4 Secondary X-ray 5 detectors 6 Control Unit 7 Spacers 10. X-ray fluorescence analyzer

Claims

1. A fluorescent X-ray analyzer for analyzing a sample, An X-ray source that irradiates the sample with primary X-rays, A means for measuring the intensity of secondary X-rays generated from the above sample, A theoretical intensity calculation means for calculating the theoretical intensity of secondary X-rays generated from each element in the above sample based on the assumed composition, A calculation means for calculating the composition of the sample by successively and approximately correcting the assumed composition so that the measured intensity of the secondary X-rays matches the theoretical intensity, Equipped with, The theoretical intensity calculation means calculates the theoretical intensity based on the product of the detection efficiency of the fluorescent X-rays, which corresponds to the sample depth (the distance from the surface of the sample irradiated with primary X-rays to the point inside the sample where secondary X-rays are emitted), the intensity of the primary X-rays, and the X-ray generation efficiency of the quantified element. The above-mentioned detection efficiency of fluorescent X-rays is determined in advance and stored so that it can be used for the analysis of multiple samples, characterized in that it is an X-ray fluorescence analyzer.

2. A fluorescent X-ray analyzer according to claim 1, The above detection efficiency is approximated as an exponential function or polynomial, and the above theoretical intensity is calculated by solving the integral of an equation obtained by multiplying the above approximated exponential function or polynomial by the intensity of the primary X-rays and the X-ray generation efficiency of the element to be quantified.

3. A fluorescent X-ray analyzer according to claim 1, The above-mentioned theoretical intensity is obtained by numerically integrating the integral of the product of the detection efficiency of the fluorescent X-rays, the intensity of the primary X-rays, and the X-ray generation efficiency of the element to be quantified, with respect to the sample depth.

4. A fluorescent X-ray analyzer according to any one of claims 1 to 3, A fluorescent X-ray analyzer characterized in that the above detection efficiency is determined based on the intensity of fluorescent X-rays emitted from each point inside the above sample, which is obtained by Monte Carlo simulation calculation or actual measurement.

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