X-ray fluorescence spectrometer

Abstract

In this X-ray fluorescence spectrometer, a quantifying means calculates and displays, as a counting accuracy, the theoretical standard deviation of a corrected differential intensity by formula (1) on the basis of a pre-correction integral intensity and a pre-correction differential intensity. (1): σW(It0, IW0) = (δIW / δIt0)2・σIt0 2 + (δIW / δIW0)2・σIW0 2)1 / 2 σW: theoretical standard deviation of corrected differential intensity It0: pre-correction integral intensity IW: pre-correction differential intensity IW: corrected differential intensity σIt0: theoretical standard deviation of pre-correction integral intensity σIW0: theoretical standard deviation of pre-correction differential intensity

Description

X-ray fluorescence analyzer Related Applications

[0001] This application claims priority to Japanese Patent Application No. 2023-097750, filed June 14, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an X-ray fluorescence 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 generated fluorescent X-rays.

[0003] 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 performed 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.

[0004] As another technique, 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.

[0005] Japanese Patent Application Laid-Open No. 2022-086669

[0006] However, because the estimation of counting accuracy using these conventional techniques does not take into account fluctuations in counting loss correction, the estimated counting accuracy becomes higher (smaller and better numerically) as the intensity of the fluorescent X-ray increases, and as a result, it has been found that in high-intensity measurements, the estimated counting accuracy is significantly higher than the actual repeatability, making it impossible to perform quantitative analysis with appropriate counting accuracy.

[0007] 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 count-loss correction, and that is capable of calculating and displaying counting accuracy that appropriately reflects fluctuations in count-loss correction.

[0008] 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 count-loss correction based on the intensity of the generated fluorescent X-rays, wherein the quantitative means calculates the theoretical standard deviation of the corrected differential intensity using the following equation (1) and displays it on a display.

[0009] 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 : Integrated intensity before correction (kcps) I W0 : Uncorrected differential intensity (kcps) I W : Corrected differential intensity (kcps) (∂I W / ∂I t0 ): I t0 I against W The partial differential coefficient of (∂I W / ∂It0 ) = ((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 : Integrated intensity after correction (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 The partial differential coefficient 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.

[0010] 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, thereby allowing fluctuations in the counting-loss correction to be appropriately reflected in the counting accuracy, thereby facilitating quantitative analysis with appropriate counting accuracy.

[0011] 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.

[0012] Any combination of at least two features disclosed in the claims and / or the specification and / or the drawings is included in the present invention. In particular, any combination of two or more of the claims is included in the present invention.

[0013] The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and explanation purposes and should not be used to define the scope of the present invention. The scope of the present invention is defined by the appended claims. In the accompanying drawings, the same part numbers in multiple drawings indicate the same parts.

[0023] Figure 1 is a schematic diagram showing an X-ray fluorescence analysis apparatus according to one embodiment of the present invention.

[0014] 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 according to 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, a counting means, and other means (not shown).

[0015] The X-ray fluorescence analyzer of this embodiment is a wavelength-dispersive scanning X-ray fluorescence analyzer and includes an interlocking means 10, i.e., a so-called goniometer, that interlocks the spectroscopic element 6 and the detector 8 so as to change the wavelength of the 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 that 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 about an axis O that passes through the center of its surface and is perpendicular to the paper surface, and rotating 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 (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.

[0016] The X-ray fluorescence 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.

[0017] 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 : Integrated intensity before correction (kcps) I W0 : Uncorrected differential intensity (kcps) I W : Corrected differential intensity (kcps) (∂I W / ∂I t0 ): I t0 I against W The partial differential coefficient 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 : Integrated intensity after correction (kcps) σ It0 : Theoretical standard deviation of uncorrected integrated intensity σ It0 = (I t0 / 1000T) 1 / 2T: Measurement time (seconds) (∂I W / ∂I W0 ): I W0 I against W The partial differential coefficient 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.

[0018] Among the values ​​related to formula (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.

[0019] Although various correction formulas are known for counting loss correction, the following formulas (2) and (3) based on the extended death time model (asphyxiation type) are used.

[0020] 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)

[0021] The corrected integrated intensity I obtained by equation (2) t is the uncorrected integrated intensity I t0The corrected differential intensity I obtained by the partial differentiation of Equation (3) W is the uncorrected differential intensity I W0 and the corrected differential intensity I obtained by equation (3) W is the uncorrected integrated intensity I t0 From the equation partially differentiated by I W0 I against W The partial differential coefficient of (∂I W / ∂I W0 ), and I t0 I against W The partial differential coefficient of (∂I W / ∂I t0 ) is required.

[0022] Generally, quantitative analysis uses corrected differential intensity I W is used, whereas 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 differential coefficient, 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 differential coefficient, or gradient (∂I W / ∂I W0 ) and calculate the root mean square of the two to obtain the theoretical standard deviation σ of the corrected differential intensity. W (I t0 , I W0 In 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 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.

[0023] 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-loss correction coefficient τ for the integrated intensity was set to 1.74 keV. d = 1.42 x 10 -7 , the counting-loss correction factor τ for the differential intensity W = 1.03 x 10 -7 Under these measurement conditions, measurements were actually performed 20 times, 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 conventional 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 by the actual repeated measurements.

[0024] 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 differential coefficient of (∂I W / ∂I W0 ) = (I W / I W0 ) / (1-I W ・τ W )=1.5464,I t0 I against W The partial differential coefficient of (∂I W / ∂I t0 ) = ((I W ・τ d ) / (1-I W ・τ W ))・((It / 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 of 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 in the counting-loss correction.

[0025] In the course 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 C.V., which is the ratio of the uncorrected integrated intensity I to the uncorrected integrated intensity I, does not decrease monotonically at high intensities. 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 C.V., which is the ratio of W opt and 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 C.V. is proportional to opt The optimally corrected differential intensity I W opt and display it on the display 15.

[0026] More specifically, this operation is performed as follows: First, the uncorrected integrated intensity I t0 and uncorrected differential intensity I W0 The relationship between the analytical line, the detector to be used, the pulse height range PHA to be detected, and other measurement conditions is determined in advance. t0 I againstW0 The coefficients of the fitting function of are stored in the quantification means 13. In addition, 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.

[0027] After the above preparation, the uncorrected integrated intensity I t0 Then, the corrected integrated intensity I t and the above-mentioned pre-corrected 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 C.V. (I W ) = σ W (I t0 , I W0 ) / I W Calculate the coefficient of variation C.V. (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.

[0028] Then, by regression calculation, the coefficient of variation C.V. (I W The corrected differential intensity at which the value of I 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 C.V. 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 The coefficient of variation C.V. (I W ) is the optimum tube current value C opt is displayed, making it easier to perform quantitative analysis with appropriate counting accuracy.

[0029] Note that simply reducing the tube current value C within the settable range does not result in the optimal corrected differential intensity I W opt 1, an attenuator 16 having a diaphragm 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 optimum corrected differential intensity I W opt and calculate the optimal corrected differential intensity I W opt The optimum tube current value C at which the coefficient of variation C.V. is minimized is opt is calculated and displayed on the display 15 together with the fact that the attenuator 16 is added.

[0030] Although the preferred embodiment has been described above with reference to the drawings, those skilled in the art will readily understand various changes and modifications within the scope of the present invention, which are within the scope of the present invention as defined by the appended claims.

[0031] 1 Unknown sample 3 Primary X-ray 4 X-ray tube 5 Fluorescent X-ray 13 Quantitative measurement means 14 Standard sample 15 Display

Claims

1. 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, wherein the quantitative means calculates the theoretical standard deviation of the corrected differential intensity using the following formula (1) and displays it on a display. 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 I W0 : Uncorrected differential intensity I W : corrected differential intensity (∂I W / ∂I t0 ): I t0 I against W The partial differential coefficient 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 error correction coefficient for differential intensity I t : Integrated intensity after correction σ It0 : Theoretical standard deviation of uncorrected integrated intensity (∂I W / ∂I W0 ): I W0 I against W The partial differential coefficient of (∂I W / ∂I W0 ) = (I W / I W0 ) / (1-I W ・τ W ) σ IW0 : Theoretical standard deviation of uncorrected differential intensity 2. A fluorescent X-ray analyzer as claimed in claim 1, wherein the quantitative means determines, 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, determines from the optimal corrected differential intensity the optimal tube current value at which the coefficient of variation is minimized and displays it on a display.

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