X-ray fluorescence analyzer

Abstract

To provide a fluorescence X-ray analysis device which performs quantitative analysis of a sample using quantification means that performs count missing correction and appropriately reflects the fluctuations of the count missing correction on counting accuracy.SOLUTION: Quantification means calculates and displays a theoretical standard deviation of the post-correction differential intensity using the equation (1) based on the pre-correction integral intensity and the pre-correction differential intensity as the counting accuracy. (1) σW(It0,IW0)=((δIW / δIt0)2 σIt02+(δIW / δIW0)2 σIW02)1 / 2 . σW: the theoretical standard deviation of the post-correction differential intensity, It0: the pre-correction integral intensity, IW0: the pre-correction differential intensity, IW: the post-correction differential intensity, σIt0: the theoretical standard deviation of the pre-correction integral intensity, σIW0: the theoretical standard deviation of the pre-correction differential intensity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fluorescent X-ray analyzer that performs quantitative analysis of a sample by irradiating the sample with primary X-rays and performing counting-loss correction based on the intensity of the fluorescent X-rays generated. [Background technology]

[0002] In general, in X-ray fluorescence analysis, counting errors become noticeable at high counting rates, i.e., at high-intensity fluorescent X-rays, so counting error correction is performed. The estimated value of counting accuracy when counting error correction is the theoretical standard deviation σ calculated from the statistical error of the intensity I (kcps) after counting error correction, that is, σ = (I / 1000T) from the intensity I (kcps) after counting error correction and the measurement time T (seconds). 1 / 2 The theoretical standard deviation σ calculated as follows is used.

[0003] As another method, in the X-ray fluorescence analyzer described in Patent Document 1, in order to perform measurements with appropriate counting time and analytical accuracy even when counting losses occur, the counting accuracy (theoretical standard deviation of intensity after counting loss correction) is estimated as the product of the counting accuracy of the pre-correction intensity, which is the intensity before counting loss correction, and the gradient of the post-correction intensity relative to the pre-correction intensity, thereby reflecting the influence of counting losses in the counting accuracy (see paragraphs 0034-0035, etc.). Note that the intensity of fluorescent X-rays includes differential intensity, which is the cumulative intensity in a predetermined pulse-height range including the peak of the analytical line (fluorescent X-ray to be analyzed), and integrated intensity, which is the cumulative intensity in the entire pulse-height range incident on the detector; however, the X-ray fluorescence analyzer described in Patent Document 1 uses the integrated intensity, as can be seen from equation (6) in paragraph 0032. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-086669 Summary of the Invention [Problem to be solved by the invention]

[0005] However, because the estimation of counting accuracy using these conventional techniques does not take into account fluctuations in counting loss correction, the higher the intensity of the fluorescent X-rays, the higher the estimated counting accuracy (smaller and better in terms of numerical value). As a result, it was found that in high-intensity measurements, the estimated counting accuracy is much higher than the actual repeatability. This makes it impossible to perform quantitative analysis with appropriate counting accuracy.

[0006] The present invention has been made in view of the above-mentioned conventional problems, and aims to provide an X-ray fluorescence analyzer that performs quantitative analysis of a sample using a quantitative means that performs counting-loss correction, and that can calculate and display counting accuracy that appropriately reflects fluctuations in counting-loss correction. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the present invention provides an X-ray fluorescence analyzer that irradiates a sample with primary X-rays from an X-ray tube and performs quantitative analysis of the sample using a quantitative means that performs counting loss correction based on the intensity of the generated fluorescent X-rays, and the quantitative means calculates the theoretical standard deviation of the corrected differential intensity using the following equation (1) and displays it on a display.

[0008] σ W (I t0 ,I W0 )=((∂I W / ∂I t0 ) 2 σ It0 2 +(∂I W / ∂I W0 ) 2 σ IW0 2 ) 1 / 2 …(1) Here, the symbols and terms in the formula are as follows, from left to right: σ W : Theoretical standard deviation of corrected differential intensity I t0 :Uncorrected integrated intensity (kcps) I W0 : Uncorrected differential intensity (kcps) I W : Corrected differential intensity (kcps) (∂I W / ∂I t0 ):I t0 I against W partial derivative of (∂I W / ∂I t0 )=((I W ·τ d ) / (1-I W ·τ W ))·(∂I t / ∂I t0 )=((I W ·τ d ) / (1-I W ·τ W ))·((I t / I t0 ) / (1-I t ·τ d )) τ d :Counting error correction factor for integrated intensity τ W :Counting loss correction factor for differential intensity I t :Corrected integrated intensity (kcps) σ It0 : Theoretical standard deviation of uncorrected integrated intensity σ It0 =(I t0 / 1000T) 1 / 2 T: Measurement time (seconds) (∂I W / ∂I W0 ):I W0 I against W partial derivative of (∂I W / ∂I W0 )=(I W / I W0 ) / (1-I W ·τ W ) σ IW0 : Theoretical standard deviation of uncorrected differential intensity σ IW0 =(I W0 / 1000T)1 / 2 The above σ It0 ,σ IW0 The specific formula is I t0 ,I W0 This is an example in which a Poisson distribution is assumed as the distribution of fluctuations, but a formula including correction terms such as counting losses or another probability distribution may also be used.

[0009] According to the X-ray fluorescence analyzer of the present invention, the quantification means calculates and displays the theoretical standard deviation of the corrected differential intensity using formula (1) based on the uncorrected integrated intensity and the uncorrected differential intensity as the counting accuracy, so that fluctuations in the counting-loss correction can be appropriately reflected in the counting accuracy, facilitating quantitative analysis with appropriate counting accuracy.

[0010] In the X-ray fluorescence analyzer of the present invention, the quantification means may determine, based on a previously determined relationship between the uncorrected integrated intensity and the uncorrected differential intensity, the corrected differential intensity at which the coefficient of variation, which is the ratio of the theoretical standard deviation of the corrected differential intensity to the corrected differential intensity, is minimized as the optimal corrected differential intensity, and, under the assumption that the tube current value of the X-ray tube is proportional to the corrected differential intensity, determine from the optimal corrected differential intensity the optimal tube current value at which the coefficient of variation, which is the ratio of the theoretical standard deviation of the corrected differential intensity to the corrected differential intensity, is minimized and displayed on the display. In this case, the optimal tube current value at which the coefficient of variation, which is the ratio of the theoretical standard deviation of the corrected differential intensity to the corrected differential intensity, is minimized is displayed, making it even easier to perform quantitative analysis with appropriate counting accuracy. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing an X-ray fluorescence analyzer according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] An X-ray fluorescence analyzer according to one embodiment of the present invention will now be described. As shown in Fig. 1, the X-ray fluorescence analyzer of this embodiment is a scanning X-ray fluorescence analyzer that measures the intensity of secondary X-rays 5 generated by irradiating primary X-rays 3 onto a sample 1, 14 (including both an unknown sample 1 and a standard sample 14). The X-ray fluorescence analyzer includes a sample stage 2 on which the sample 1, 14 is placed, an X-ray tube 4 that irradiates the sample 1, 14 with the primary X-rays 3, a spectroscopic element 6 that disperses secondary X-rays 5, such as fluorescent X-rays, generated from the sample 1, 14, and a detector 8 that receives secondary X-rays 7 dispersed by the spectroscopic element 6 and detects their intensity. The output of the detector 8 is input to control means 11, such as a computer, which controls the entire apparatus, via an amplifier, a pulse-height analyzer, and a counting means (not shown).

[0013] The X-ray fluorescence analyzer of this embodiment is a wavelength-dispersive scanning X-ray fluorescence analyzer and includes interlocking means 10, i.e., a so-called goniometer, that interlocks the spectroscopic element 6 and detector 8 so as to change the wavelength of secondary X-rays 7 incident on the detector 8. When secondary X-rays 5 are incident on the spectroscopic element 6 at a certain incident angle θ, an extension line 9 of the secondary X-rays 5 and the secondary X-rays 7 dispersed (diffracted) by the spectroscopic element 6 form a spectral angle 2θ, which is twice the incident angle θ. The interlocking means 10 changes the spectral angle 2θ to change the wavelength of the dispersed secondary X-rays 7, while rotating the spectroscopic element 6 around an axis O that passes through the center of its surface and is perpendicular to the paper surface, and then rotates the detector 8 around the axis O by twice the rotation angle along a circle 12 so that the dispersed secondary X-rays 7 are incident on the detector 8. The value of the spectral angle 2θ (the 2θ angle) is input from the interlocking means 10 to the control means 11. In the present invention, the X-ray fluorescence analyzer may be a wavelength dispersive and multi-element simultaneous analysis type X-ray fluorescence analyzer, or an energy dispersive type X-ray fluorescence analyzer.

[0014] The fluorescent X-ray analyzer of this embodiment is provided with a quantification means 13 as a program installed in the control means 11, and quantitative analysis of the samples 1 and 14 is performed by the quantification means 13 that performs counting loss correction based on the measured intensity of the fluorescent X-rays 5. The quantification means 13 calculates the theoretical standard deviation σ of the corrected differential intensity using the following equation (1): W (I t0 ,I W0) is calculated and displayed on a display 15 such as a liquid crystal display connected to the control means 11.

[0015] σ W (I t0 ,I W0 )=((∂I W / ∂I t0 ) 2 σ It0 2 +(∂I W / ∂I W0 ) 2 σ IW0 2 ) 1 / 2 …(1) Here, the symbols and terms in the formula are as follows, from left to right: σ W : Theoretical standard deviation of corrected differential intensity I t0 :Uncorrected integrated intensity (kcps) I W0 : Uncorrected differential intensity (kcps) I W : Corrected differential intensity (kcps) (∂I W / ∂I t0 ):I t0 I against W partial derivative of (∂I W / ∂I t0 )=((I W ·τ d ) / (1-I W ·τ W ))·(∂I t / ∂I t0 )=((I W ·τ d ) / (1-I W ·τ W ))·((I t / I t0 ) / (1-I t ·τ d )) τ d :Counting error correction factor for integrated intensity τ W :Counting loss correction factor for differential intensity I t:Corrected integrated intensity (kcps) σ It0 : Theoretical standard deviation of uncorrected integrated intensity σ It0 =(I t0 / 1000T) 1 / 2 T: Measurement time (seconds) (∂I W / ∂I W0 ):I W0 I against W partial derivative of (∂I W / ∂I W0 )=(I W / I W0 ) / (1-I W ·τ W ) σ IW0 : Theoretical standard deviation of uncorrected differential intensity σ IW0 =(I W0 / 1000T) 1 / 2 The above σ It0 ,σ IW0 The specific formula is I t0 ,I W0 This is an example in which the Poisson distribution is assumed as the distribution of fluctuations.

[0016] Among the values ​​related to Equation (1), the uncorrected integrated intensity I t0 and uncorrected differential intensity I W0 is obtained by measurement as in the conventional device, and the counting-loss correction factor τ d , the counting loss correction factor τ for the differential intensity W The measurement time T is also acquired by inputting it into the control means 11 as a measurement condition together with the analysis line, the detector to be used, the pulse height range PHA to be detected, etc., in the same way as in the conventional device.

[0017] Although various correction formulas are known for counting loss correction, we use the following formulas (2) and (3) based on the extended death time model (asphyxiation type).

[0018] I t =I t0 exp(I t·τ d ) …(2) I W =I W0 exp(I t ·τ d )exp(I W ·τ W ) …(3)

[0019] The corrected integrated intensity I obtained by equation (2) t is the uncorrected integrated intensity I t0 The corrected differential intensity I obtained by partial differentiation with Eq. (3) W is the uncorrected differential intensity I W0 The partial derivative of the equation and the corrected differential intensity I obtained by equation (3) W is the uncorrected integrated intensity I t0 From the partial differential equation, the above, I W0 I against W The partial derivative of (∂I W / ∂I W0 ), and I t0 I against W The partial derivative of (∂I W / ∂I t0 ) is required.

[0020] Generally, quantitative analysis uses corrected differential intensity I W is used, in equation (1), the uncorrected integrated intensity I t0 and uncorrected differential intensity I W0 are assumed to be independent, and the theoretical standard deviation of the uncorrected integrated intensity σ It0 and the uncorrected integrated intensity I t0 Corrected differential intensity I W The partial derivative of, or gradient (∂I W / ∂I t0 ) and the theoretical standard deviation of the uncorrected differential intensity σ IW0 and the uncorrected differential intensity I W0 Corrected differential intensity I W The partial derivative of, or gradient (∂I W / ∂I W0 ) and calculate the root mean square of the two to obtain the theoretical standard deviation of the corrected differential intensity σ W (I t0 ,I W0In the X-ray fluorescence analyzer of the present invention, the theoretical standard deviation σ of the corrected differential intensity is calculated. W (I t0 ,I W0 ) is displayed as the counting accuracy, so that the fluctuations in the counting-loss correction can be appropriately reflected in the counting accuracy. Therefore, quantitative analysis can be easily performed with appropriate counting accuracy.

[0021] The effects of the present invention were verified as follows: For Si-Kα radiation (1.74 keV), a PC detector was used, the pulse height range PHA was set to 100-300, the measurement time T was set to 20 seconds, and the counting error correction coefficient τ for the integrated intensity was set to d =1.42×10 -7 , the counting loss correction factor τ for the differential intensity W =1.03×10 -7 Under these measurement conditions, 20 repeated measurements were performed, and the corrected differential intensity I W The standard deviation of the corrected differential intensity I was 0.374. W The average value of the corrected differential intensity I was 1207.44 (kcps). W The theoretical standard deviation calculated from the statistical error is (1207.44 / (1000×20)) 1 / 2 =0.246, which is 34% smaller (highly accurate, good) than the standard deviation of 0.374 obtained from the actual repeated measurements.

[0022] In contrast, in the X-ray fluorescence analyzer of the present invention, the uncorrected integrated intensity I t0 Average value: 1052.94 (kcps), uncorrected differential intensity I W0 Average value: 891.68 (kcps), theoretical standard deviation of uncorrected integrated intensity σ It0 =(I t0 / 1000T) 1 / 2 =0.229, theoretical standard deviation of uncorrected differential intensity σ IW0 =(I W0 / 1000T) 1 / 2 =0.211, I W0 I against W The partial derivative of (∂I W / ∂I W0 )=(I W / I W0 ) / (1-I W ·τ W )=1.5464, I t0 I against W The partial derivative of (∂I W / ∂I t0 )=((I W ·τ d ) / (1-I W ·τ W ))·((I t / I t0 ) / (1-I t ·τ d )) = 0.2851, and from equation (1), the corrected differential intensity I W The theoretical standard deviation of the corrected differential intensity, σ, is sufficiently close (only 11% smaller) to the standard deviation of 0.374 W Thus, according to the X-ray fluorescence analyzer of the present invention, the theoretical standard deviation σ of the corrected differential intensity as the counting accuracy is estimated to be W (I t0 ,I W0 ) can appropriately reflect the fluctuations of the counting-loss correction.

[0023] In the process of examining the fluctuations in the counting loss correction, the inventors of the present application have found that the corrected differential intensity I W Theoretical standard deviation of the corrected differential intensity σ W It was found that the coefficient of variation CV, which is the ratio of the uncorrected integrated intensity I t0 and uncorrected differential intensity I W0 Based on the relationship between the corrected differential intensity I W Theoretical standard deviation of the corrected differential intensity σ W The coefficient of variation CV is the ratio of the optimal corrected differential intensity I W opt The tube current value C of the X-ray tube 4 is calculated as the corrected differential intensity I W Based on the assumption that the coefficient of variation CV is proportional to opt The optimal corrected differential intensity IW opt and display it on the display 15.

[0024] More specifically, this operation is performed as follows: First, the uncorrected integrated intensity I t0 and uncorrected differential intensity I W0 The relationship between I and I is determined in advance depending on the measurement conditions such as the analytical line, the detector used, and the pulse height range PHA to be detected. t0 I against W0 The coefficients of the fitting function of are stored in the quantification means 13. Also, as with the conventional device, the tube current value C mes and the corrected differential intensity of the analytical line I W mes The counting loss correction factor τ for the integrated intensity is obtained. d , the counting loss correction factor τ for the differential intensity W As described above, the measurement conditions are input to the control means 11 and acquired in the same manner as in the conventional device.

[0025] After the above preparation, the uncorrected integral intensity I t0 Then, the corrected integrated intensity I t and the uncorrected integrated intensity I t0 and uncorrected differential intensity I W0 The uncorrected differential intensity I W0 Next, the uncorrected differential intensity I W0 , integrated intensity I after correction t Then, the corrected differential intensity I W and then calculate the corrected differential intensity I W Using the above formula (1), the coefficient of variation CV(I W )=σ W (I t0 ,I W0 ) / I W Calculate the coefficient of variation CV(I W ) is determined depending on the measurement conditions such as the analytical line, the detector used, and the pulse height range PHA to be detected.

[0026] Then, by regression calculation, the coefficient of variation CV(I W The corrected differential intensity at which the value of is minimized is called the optimal corrected differential intensity I W opt Furthermore, the tube current value C of the X-ray tube 4 is calculated as the corrected differential intensity I W Based on the assumption that the coefficient of variation CV is proportional to opt , the optimal corrected differential intensity I W opt From C opt =C mes ×(I W opt / I W mes ) and displayed on the display 15. In this case, the corrected differential intensity I W Theoretical standard deviation of the corrected differential intensity σ W (I t0 ,I W0 ) is the coefficient of variation CV(I W ) is the optimum tube current value C opt is displayed, making it easier to perform quantitative analysis with appropriate counting accuracy.

[0027] However, simply reducing the tube current C within the settable range does not improve the optimal corrected differential intensity I W opt If the corrected differential intensity I is not obtained, as shown in FIG. 1, an attenuator 16 having an aperture is advanced into the optical path of the fluorescent X-ray 5 by an advance / retract mechanism 17, thereby attenuating the fluorescent X-ray 7 incident on the detector 8. It is a known technique to use the attenuator 16 having a predetermined attenuation rate in combination with the control of the tube current value C. When the attenuator 16 is used, the quantifying means 13 calculates the corrected differential intensity I attenuated by the predetermined attenuation rate of the attenuator 16. W The optimal corrected differential intensity I, which minimizes the coefficient of variation CV, is W opt and calculate the optimal corrected differential intensity I W opt The optimum tube current value C at which the coefficient of variation CV is minimized is opt is calculated and displayed on the display 15 together with the fact that the attenuator 16 is added. [Explanation of symbols]

[0028] 1. Unknown sample 3 Primary X-ray 4 X-ray tube 5. X-ray fluorescence 13 Quantitative means 14 Standard Samples 15 Display

Claims

1. 1. An X-ray fluorescence analyzer for quantitatively analyzing a sample by irradiating a sample with primary X-rays from an X-ray tube and performing count-loss correction based on the intensity of the generated fluorescent X-rays, The quantitative means calculates the theoretical standard deviation of the corrected differential intensity using the following formula (1), and displays it on a display. s Ｗ (I) ｔ０ ,I Ｗ０ )=((∂I Ｗ / ∂I ｔ０ ) ２ ・s Ｉｔ０ ２ +(∂I Ｗ / ∂I Ｗ０ ) ２ ・s ＩＷ０ ２ ) １／２ …(1) Here, the symbols and terms in the formula are as follows, from left to right: σ Ｗ : theoretical standard deviation of corrected differential intensity I ｔ０ : uncorrected integrated intensity I Ｗ０ : Uncorrected differential intensity I Ｗ : corrected differential intensity (∂I Ｗ / ∂I ｔ０ ): I ｔ０ I against Ｗ partial derivative of (∂I) Ｗ / ∂I ｔ０ )=((A Ｗ ・t ｄ ) / (1-A Ｗ ・t Ｗ ))・(∂I ｔ / ∂I ｔ０ )=((A Ｗ ・t ｄ ) / (1-9 Ｗ ・t Ｗ ))・((I ｔ / I ｔ０ ) / (1-A ｔ ・t ｄ )) τ ｄ : counting error correction factor for integrated intensity τ Ｗ : counting loss correction factor for differential intensity I ｔ Integral strength after correction σ Ｉｔ０ : Theoretical standard deviation of uncorrected integrated intensity (∂I Ｗ / ∂I Ｗ０ ): I Ｗ０ I against Ｗ partial derivative of (∂I Ｗ / ∂I Ｗ０ )=(I Ｗ / I Ｗ０ ) / (1-I Ｗ ・τ Ｗ ) σ ＩＷ０ : theoretical standard deviation of uncorrected differential intensity

2. 2. The X-ray fluorescence analyzer according to claim 1, The quantification means Based on the relationship between the uncorrected integrated intensity and the uncorrected differential intensity that has been obtained in advance, a coefficient of variation, which is the ratio of the theoretical standard deviation of the corrected differential intensity to the corrected differential intensity, is determined as the optimal corrected differential intensity, and An X-ray fluorescence analyzer that, under the assumption that the tube current value of the X-ray tube is proportional to the corrected differential intensity, determines the optimum tube current value that minimizes the coefficient of variation from the optimum corrected differential intensity and displays it on a display.

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