JP4279983B2 - X-ray fluorescence analyzer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for correcting the influence of characteristic X-rays from an X-ray tube in a fluorescent X-ray analyzer that analyzes the composition of a sample by an FP method.
[0002]
[Prior art]
Conventionally, in fluorescent X-ray analysis, a sample is irradiated with primary X-rays from an X-ray tube, and the intensity of the generated fluorescent X-rays is measured with a detector or the like to analyze the composition of the sample. From the tube, in addition to the characteristic X-rays of the target element, characteristic X-rays of the substances attached to the X-ray tube window and the elements of the structure in the X-ray tube, so-called impure lines, are generated. When this impure line is scattered by the sample and detected by the detector, it cannot be distinguished from fluorescent X-rays of the same wavelength generated from the components in the sample.
[0003]
On the other hand, for example, in the fundamental parameter method, that is, the FP method, the fluorescence X calculated by assuming the converted intensity to the theoretical intensity scale based on the measured intensity of fluorescent X-rays and the content of each component (sample composition) in the sample. The theoretical intensity of the line is compared for each corresponding component, and the assumed content rate of each component is calculated by successive approximation so that both intensities match, and the content rate of each component is calculated. In order to correct for the influence of the line, the scattering intensity of the impure line is measured in advance using a blank sample that does not contain a component that uses fluorescent X-rays of the same wavelength as the impure line as the analysis line, and the analysis line in the sample to be analyzed is analyzed. By subtracting from the measured intensity at the wavelength of 1, the measured intensity of only the fluorescent X-rays generated from the components in the sample was obtained.
[0004]
[Problems to be solved by the invention]
However, since the measured intensity of the impure line is affected by the composition of the sample, the influence of the impure line cannot be accurately corrected when the composition of the blank sample and the sample to be analyzed are greatly different. In addition, it is actually very difficult to prepare a huge number of blank samples and measure the scattering intensity of impure lines in order to deal with samples of all kinds. A similar problem occurs when the target element of the X-ray tube is included in the sample. That is, in such a case, the characteristic X-rays from the target of the X-ray tube are generated from the X-rays generated from the X-ray tube using a primary filter so as not to overlap the fluorescent X-rays generated from the sample. Although it is removed to form a primary X-ray, it cannot be completely removed, and its influence cannot be corrected accurately as in the case of the impure line described above. Further, the correction of the influence of the characteristic X-ray from the X-ray tube is not only performed when the wavelength of the characteristic X-ray from the analysis line and the X-ray tube is the same, that is, the same characteristic X-ray. It is also necessary when the spectrum approaches and the spectra overlap.
[0005]
The present invention has been made in view of the above-described conventional problems, and provides an apparatus capable of sufficiently accurately correcting the influence of characteristic X-rays from an X-ray tube in a fluorescent X-ray analyzer that analyzes the composition of a sample by the FP method. The purpose is to do.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, an X-ray fluorescence analyzer of the present invention comprises an X-ray tube that irradiates a sample with primary X-rays, and detection means that measures the intensity of secondary X-rays generated from the sample. In addition, the converted intensity to the theoretical intensity scale based on the measured intensity of fluorescent X-rays measured by the detection means and the theoretical intensity of fluorescent X-ray calculated on the assumption of the content of each component in the sample for each corresponding component In contrast to the above, a calculation means for calculating the content ratio of each component by sequentially correcting and calculating the assumed content ratio of each component so that both intensities coincide with each other is provided. That is, it is a fluorescent X-ray analyzer that performs analysis by the FP method.
[0007]
Here, the calculation means uses a sample having a known composition at the wavelength of the analytical line for a component having a fluorescent X-ray whose spectrum overlaps with the characteristic X-ray from the X-ray tube. The characteristic X-ray scattering from the X-ray tube in the sample to be analyzed based on the impure line device sensitivity constant representing the correlation between the theoretical intensity and the measured intensity of the scattered X-ray from the X-ray tube. The measured intensity of the line is estimated from the theoretical intensity, and subtracted from the measured intensity by the detection means, and used as the measured intensity of the fluorescent X-ray generated from the sample to be analyzed.
[0008]
According to the X-ray fluorescence analyzer of the present invention, in the FP method, the measured intensity of scattered X-rays from the characteristic X-ray tube is estimated from the theoretical intensity calculated according to the composition of the sample. The effect of characteristic X-rays from can be corrected sufficiently accurately.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an apparatus according to an embodiment of the present invention will be described with reference to FIG. First, the configuration of this apparatus will be described. This apparatus includes a sample stage 8 on which a sample 13 is placed, an X-ray tube 1 that irradiates the sample 13 with primary X-rays 2, and the intensity of secondary X-rays 4 such as fluorescent X-rays generated from the sample 13. And detecting means 10 for measuring. The detection means 10 includes a spectroscopic element 5 that splits the secondary X-ray 4 generated from the sample 13 and a detector 7 that measures the intensity of the secondary X-ray 6 dispersed by the spectroscopic element 5.
[0010]
In addition, this apparatus uses the converted intensity to the theoretical intensity scale based on the measured intensity of the fluorescent X-ray 4 measured by the detection means 10 and the theoretical intensity of the fluorescent X-ray calculated by assuming the content of each component in the sample 13. And calculating means 16 for calculating the content ratio of each component by sequentially correcting and calculating the assumed content ratio of each component so that both intensities coincide with each other. Yes. That is, the apparatus of this embodiment is a fluorescent X-ray analyzer that performs analysis by the FP method.
[0011]
Here, the calculation means 16 of this apparatus, for a component whose analysis line is the fluorescent X-ray 4 whose spectrum overlaps with the characteristic X-ray from the X-ray tube 1, is a sample 3 whose composition is known at the wavelength of the analysis line. , 23 based on the impure line device sensitivity constant representing the correlation between the theoretical intensity and the measured intensity of the scattered X-ray 4 of the characteristic X-ray from the X-ray tube 1 obtained in advance, using the sample 13 to be analyzed. The measured intensity of the scattered X-ray 4 of the characteristic X-ray from the X-ray tube 1 is estimated from the theoretical intensity, and subtracted from the measured intensity by the detection means 10 to obtain the measured intensity of the fluorescent X-ray 4 generated from the sample 13 to be analyzed. Use. The characteristic X-rays from the X-ray tube 1 include the characteristic X-rays of the substances attached to the window of the X-ray tube 1 and the elements of the structure in the X-ray tube 1, so-called impure lines, and the characteristic X of the target element. There is a line. Samples 3 and 23 having known compositions used for determining the impure line device sensitivity constant include standard sample 3 whose composition approximates that of sample 13 to be analyzed, and characteristic X-rays and spectra from X-ray tube 1. There is a blank sample 23 which does not contain a component having the overlapping fluorescent X-rays 4 as analysis lines.
[0012]
In the calculation means 16 of this apparatus, fluorescent X-ray apparatus sensitivity coefficients A, B, and C and impurity line apparatus sensitivity constants a, b, and c are obtained and stored in advance as follows. First, the X-ray fluorescence apparatus sensitivity coefficients A, B, and C are obtained from the following equation (1) using the measured intensity I _FM and the calculated theoretical intensity I _FT measured for the standard sample 3 whose composition is known with this apparatus. It is done.
[0013]
I _FT = AI _FM ² + BI _FM + C (1)
[0014]
Here, taking as an example a case where a sample 13 including a component having a fluorescent X-ray 4 having the same wavelength as an impure line as an analysis line is to be analyzed, such a component is expressed by the following equation (2). The measured intensity I _{FM of} only the fluorescent X-ray 4 generated from the standard sample 3 is the total measured intensity (net intensity with the background removed) of the measured intensity I _IM of the scattered scattered light 4 of the impure line at the wavelength. ) _Subtract from ITM. For other components, the total measurement intensity I _TM is used as it is as the measurement intensity I _FM of only the fluorescent X-rays 4 generated from the standard sample 3 as in the normal FP method.
[0015]
I _FM = I _TM −I _IM (2)
[0016]
The measured intensity I _IM of the impure scattered ray 4 can be estimated as follows. First, impure line device sensitivity constants a, b and c representing the correlation between the theoretical intensity and the measured intensity of the scattered scattered light 4 of the impure line are converted into X-ray fluorescence apparatus sensitivity coefficients A, B and C by the above-described normal FP method. In this apparatus, the measured intensity I of the impure line scattered ray 4 measured with respect to the blank sample 23 having a known composition and not including the component having the fluorescent X-ray 4 having the same wavelength as the impure line as the analysis line. It can be obtained from the following equation (3) using the theoretical intensity I _IT of _IM and the calculated impurity scattered ray (Thomson scattered ray), and is stored in the calculating means 16 in advance. Then, based on the impure line device sensitivity constants a, b, and c, the measured intensity I _IM of the impure line scattered line 4 is calculated from the impure line scattered line in the standard sample 3 as shown in Equation (3). Estimated from the theoretical intensity I _{IT of} . As the blank sample 23, SiO ₂ or an acrylic plate can be used. In addition, the standard sample 3 used when calculating | requiring fluorescent X-ray apparatus sensitivity coefficient A, B, C about each component may also contain the component which uses the fluorescent X-ray 4 of the same wavelength as an impure line as an analysis line.
[0017]
I _IM = aI _IT ² + bI _IT + c (3)
[0018]
When a single blank sample 23 is used, a = c = 0 may be set.
[0019]
The X-ray apparatus sensitivity coefficients A, B, and C and the impurity apparatus sensitivity constants a, b, and c for components using the fluorescent X-ray 4 having the same wavelength as that of the impure line as the analysis line may be obtained as follows. it can.
[0020]
That is, an expression obtained by assigning expression (3) to expression (2) is assigned to expression (1) to obtain the following expression (1-2).
[0021]
I _FT = A (I _TM −aI _IT ² −bI _IT −c) ² + B (I _TM −aI _IT ² −bI _IT −c) + C (1-2)
[0022]
Using the total measured intensity I _TM measured for the standard sample 3 whose composition is known with this apparatus, the calculated theoretical intensity I _FT, and the theoretical intensity I _IT of the impure line scattered line, the impure line is obtained from the equation (1-2). X-ray apparatus sensitivity coefficients A, B, and C and impure line apparatus sensitivity constants a, b, and c for components having the X-ray fluorescence 4 having the same wavelength as the analysis line are simultaneously obtained. Also in this case, a = c = 0 may be set. Further, the standard sample 3 to be used may be one that does not include a component having the fluorescent X-ray 4 having the same wavelength as the impurity line as an analysis line.
[0023]
Next, the operation of the apparatus of this embodiment will be described by taking as an example the case of correcting the influence of impure lines. The sample 13 placed on the sample stage 8 is irradiated with the primary X-ray 2 and the intensity of the secondary X-ray 4 generated from each component (element) of the sample 13 is measured. Based on this measured intensity, the calculation means 16 calculates the content of each component by the FP method, for example, according to the following procedure.
[0024]
(Step 1)
Calculate the converted intensity based on each measured intensity. That is, for each component, the measured intensity I _FM is converted into a theoretical intensity scale using the fluorescent X-ray apparatus sensitivity coefficients A, B, and C as converted intensity I _FT ^M as in the previous equation (1). Here, for the components to be analyzed line X-ray fluorescence 4 having the same wavelength as impure line, not deducted measured intensity I _IM scattered radiation 4 of impure lines, fluorescent X generated total measured intensity I _TM directly from the sample _Used as measured intensity IFM of line 4 only.
[0025]
(Step 2)
From the intensity ratio between the converted intensity I _FT ^M for each component and the theoretical intensity I _FT of fluorescent X-rays from the pure substance of that component, the initial value of the content W of each component is assumed.
[0026]
(Step 3)
From the assumed composition, the theoretical intensities I _FT and I _IT of the scattered X-rays and impure rays are calculated.
[0027]
(Step 4)
The component to be analyzed line X-ray fluorescence 4 having the same wavelength as impure line, using the theoretical intensity I _IT of scattered radiation calculated impure lines, recalculate the converted intensity I _FT ^M obtained in step 1. That is, as shown in the previous equation (3), the measured intensity I _IM of the impure line scattered radiation 4 is calculated based on the impure line apparatus sensitivity constants a, b, and c, and the calculated impulsive scattered light theoretical intensity I _{IT is} calculated. The measured intensity I _IM of the estimated impulsive scattered radiation 4 is subtracted from the total measured intensity I _TM as shown in the previous equation (2), and only the fluorescent X-ray 4 generated from the sample 13 is measured. Used as intensity I _FM . Then, the measured intensity I _{FM of} only the fluorescent X-ray 4 generated from the sample 13 is converted into a theoretical intensity scale using the fluorescent X-ray apparatus sensitivity coefficients A, B, and C as shown in the previous equation (1). The new converted intensity I _FT ^M for the next step 5 is used. For other components, the converted intensity I _FT ^M obtained in step 1 is used as it is.
[0028]
(Step 5)
For each component, the content rate is updated by the following equation (4) from the converted intensity I _FT ^M obtained in step 1 or 4 and the theoretical intensity I _FT calculated in step 3. Here, W ^{(n + 1)} is the content of the n + 1th time, W ⁽ⁿ⁾ is the content of the nth time, I _FT ^{M (n)} is the converted intensity of the nth time (fluorescent X-ray 4 having the same wavelength as the impurity line ⁾ For the component having the analysis line as the analysis line, the measured intensity I _IM of the impure line scattered line 4 has been removed in step 4), and I _FT ⁽ⁿ⁾ is the nth theoretical intensity.
[0029]
W ^{(n + 1)} = W ⁽ⁿ⁾ * ( _IFTM ⁽ⁿ⁾ / _IFT ⁽ⁿ⁾ ) (4)
[0030]
(Step 6)
For each component, the n-th content rate and the (n + 1) -th content rate are compared, and convergence is determined when the change in the content rate of all the components becomes a predetermined value or less. If not converged, the procedure from step 3 is repeated.
[0031]
That is, the converted intensity obtained in step 1 or 4 and the theoretical intensity of fluorescent X-ray calculated in step 3 assuming the content of each component in step 2 are compared for each corresponding component in steps 5 and 6. By repeating steps 3 to 6, the assumed content ratios of the respective components are successively corrected so as to match the two intensities, thereby calculating the content ratios of the respective components.
[0032]
As described above, according to the fluorescent X-ray analyzer of the present embodiment, the measured intensity I _IM of the impure-line scattered radiation 4 is estimated from the theoretical intensity I _IT calculated according to the composition of the sample 13 in the FP method. Therefore, the influence of the impure line can be corrected sufficiently accurately.
[0033]
The above is an example in which the sample 13 including the component having the fluorescent X-ray 4 having the same wavelength as the impurity line as the analysis line is analyzed while correcting the influence of the impurity line. The same can be dealt with when the target element is included. That is, in such a case, the characteristic X-rays from the target of the X-ray tube 1 are converted into X-rays using a primary filter (not shown) so as not to overlap the fluorescent X-rays 4 generated from the sample 13. The primary X-ray 2 is removed from the X-rays generated from the X-ray tube 1, but the portion that cannot be completely removed is treated in the same manner as the above-described impure line, and its influence is corrected. Therefore, by estimating the measured intensity I _IM of the scattered X-ray 4 of the characteristic X-ray from the target of the X-ray tube 1 from the theoretical intensity I _IT calculated according to the composition of the sample 13, The effect of characteristic X-rays can be corrected sufficiently accurately.
[0034]
Now, in the case where the spectrum of the characteristic X-ray from the X-ray tube 1 overlaps, as described above, the wavelength of the characteristic X-ray from the analytical line and the X-ray tube 1 is the same, that is, the same characteristic X-ray ( In addition to the case of Rh-Kα ray, for example, when the two wavelengths are different but the spectra overlap each other (for example, the analysis line is a Cd-Kα ray and the characteristic X-ray from the X-ray tube 1 is Rh − If a Kbeta _2-wire) there is, it is necessary to correct the influence of the characteristic X-rays from the X-ray tube 1 in this case. Also in this case, the impure wire device sensitivity constants a, b, and c are for the wavelength of the analytical line, and the measured intensity and theoretical intensity at the wavelength of the analytical line are used to calculate the equation (1) or (1-2). It is requested from.
[0035]
【The invention's effect】
As described above in detail, according to the fluorescent X-ray analysis apparatus of the present invention, in the FP method, the theoretical intensity calculated from the measured intensity of scattered X-rays from the X-ray tube according to the composition of the sample is calculated. Therefore, the influence of characteristic X-rays from the X-ray tube can be corrected sufficiently accurately.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an X-ray fluorescence analyzer according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... X-ray tube, 2 ... Primary X-ray, 3,23 ... Sample with known composition, 4 ... Secondary X-ray generated from sample, 10 ... Detection means, 13 ... Sample to be analyzed, 16 ... Calculation means .

Claims (1)

An X-ray tube that irradiates the sample with primary X-rays;
Detection means for measuring the intensity of secondary X-rays generated from the sample;
The converted intensity to the theoretical intensity scale based on the measured intensity of fluorescent X-rays measured by the detection means and the theoretical intensity of fluorescent X-ray calculated on the assumption of the content of each component in the sample are compared for each corresponding component. In the fluorescent X-ray analysis apparatus comprising: a calculation means for calculating the content ratio of each component by sequentially correcting and calculating the content ratio of each assumed component so that the two intensities match.
For the component in which the calculation means uses the fluorescent X-ray whose spectrum overlaps with the characteristic X-ray from the X-ray tube as the analysis line, the above-mentioned calculation was performed using a sample having a known composition at the wavelength of the analysis line. Based on the impure line device sensitivity constant representing the correlation between the theoretical intensity and the measured intensity of the characteristic X-ray scattered ray from the X-ray tube, the characteristic X-ray scattered ray from the X-ray tube in the sample to be analyzed A fluorescent X-ray analysis apparatus characterized in that a measurement intensity is estimated from a theoretical intensity and is subtracted from a measurement intensity obtained by the detection means and used as a measurement intensity of fluorescent X-rays generated from a sample to be analyzed.

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