JP4237891B2 - Background correction method for fluorescent X-ray analyzer and fluorescent X-ray analyzer using the method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a background correction method for a fluorescent X-ray analyzer and a fluorescent X-ray analyzer using the method, and more specifically, due to a device cause other than a sample such as scattering by air in an X-ray irradiation range. The present invention relates to a method for correcting a background of a fluorescent X-ray analyzer and a fluorescent X-ray analyzer that realizes accurate quantification by deriving a background and taking into account the calculation.
[0002]
[Prior art]
Conventionally, there is an excitation method as a method for measuring the concentration of a component to be measured such as sulfur contained in crude oil or petroleum products. This analysis method will be briefly described with reference to FIG. 4. In FIG. 4, 1 is an X-ray tube, and X-rays (primary X-rays) 2 generated in the X-ray tube 1 are accommodated in an appropriate container. When the sample (for example, crude oil) 3 is irradiated, secondary X-rays are generated. That is, some of the primary X-rays 2 excite atoms in the sample 3 to generate fluorescent X-rays, but most of the remaining primary X-rays 2 are scattered by the sample 3. Reference numeral 4 in the figure represents secondary X-rays composed of these fluorescent X-rays and scattered X-rays.
[0003]
The scattered X-rays have substantially the same energy as the primary X-ray 2, and most of the scattered X-rays are 4.5 keV titanium characteristic X-rays when a titanium target X-ray tube is used. And if the intensity | strength of the primary X-ray 2 is the same, the quantity of the fluorescent X-ray | X_line (energy 2.3 keV) of the generated sulfur will be substantially proportional to the quantity of the sulfur contained in the sample 3.
[0004]
The scattered X-rays and fluorescent X-rays generated from the sample 3 due to the irradiation of the sample 3 with the primary X-ray 2 pass through a filter F formed by, for example, niobium for removing X-rays caused by argon in the air. Then, it enters an X-ray detector 5 comprising a proportional coefficient tube and is converted into an electric signal, and then enters an wave height analyzer (single channel analyzer or multichannel analyzer) 7 through an amplifier 6 to obtain an energy spectrum. It is done. Further, the obtained energy spectrum is processed by the CPU 8 to obtain the concentration of the measurement target component in the sample 3.
[0005]
FIG. 5 schematically shows an energy spectrum when sulfur fluorescent X-rays are measured, and the CPU 8 corresponds to a region corresponding to sulfur fluorescent X-rays (indicated by symbol S) and scattered X-rays in this spectrum. The sulfur concentration in the sample 3 can be obtained from the ratio to the region (indicated by symbol B), that is, the X-ray intensity ratio between the fluorescent X-rays and the scattered X-rays.
[0006]
FIG. 6 is a diagram showing a calibration curve representing the relationship between the X-ray intensity ratio between fluorescent X-rays and scattered X-rays and the sulfur concentration, and was obtained using a standard sample with a known sulfur concentration. In other words, this concentration measurement method utilizes the fact that both fluorescent X-rays and scattered X-rays are similarly affected by absorption by the coexisting elements, and this calculation reduces the influence of the coexisting elements. be able to.
[0007]
[Problems to be solved by the invention]
However, in recent years, the regulation level of pollutants has become extremely high, and it has become necessary to analyze components to be measured at a much lower concentration. When the concentration of the element to be measured is low, the fluorescent X-ray intensity decreases, and accordingly, the background b caused by the apparatus other than the sample, such as scattering by air in the X-ray irradiation range, cannot be ignored. It has become.
[0008]
FIG. 7 schematically shows an energy spectrum when fluorescent X-rays of low concentration sulfur are measured with a proportional counter. In this spectrum, a region S corresponding to sulfur fluorescent X-rays is an element Ss generated by excitation of sulfur contained in the sample 3 and a back surface generated by excitation of the filter F by scattered X-rays scattered by the sample 3. A ground a and a background b due to device factors such as air are included.
[0009]
As shown in FIG. 4, the background b includes X-rays 2 f generated by exciting niobium by the X-rays 2 ′ scattered by the air A within the X-ray irradiation range hitting the niobium filter F. Thus, the X-ray 2f generated by the niobium excitation has almost the same X-ray energy characteristics as the sulfur to be measured. In addition, the background b includes X-rays generated due to various apparatus factors.
[0010]
Since the background b is a portion that is not influenced by the coexisting elements of the sample 3 unlike the background a, the influence of the coexisting elements appears as a ratio of the background b to the X-ray measurement value. In other words, correction was insufficient with the simple X-ray intensity ratio (S / B) described above. That is, as the absorption by the coexisting elements contained in the sample 3 increases and the scattered light decreases, the influence of the background b increases. For this reason, conventionally, it has been necessary to calibrate the calibration curve using a standard sample every time the type of the sample 3 to be measured changes.
[0011]
The present invention has been made in consideration of the above-mentioned matters, and the object of the present invention is to accurately quantify even a low-concentration sample in a fluorescent X-ray analyzer with little influence of coexisting elements. An object of the present invention is to provide a method for correcting the background of a fluorescent X-ray analyzer that can be analyzed, and a fluorescent X-ray analyzer using the method.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the background correction method of the X-ray fluorescence analyzer of the present invention is the X-ray fluorescence intensity and scattered X-rays measured by the X-ray detector when the sample is irradiated with X-rays. Using the X-ray intensity ratio with the intensity and the calibration curve obtained using the standard sample, the absorption effect of the coexisting elements contained in the sample in the same manner as both the fluorescent X-rays and the scattered X-rays of the sample is made the same. In the fluorescent X-ray analyzer configured to calculate the concentration of the measurement target component in the sample by using the received X-ray fluorescence intensities of a plurality of constant concentration samples having the same measurement target component concentration and different coexisting elements The scattered X-ray intensity is measured, and the X-ray intensity ratio of each constant-concentration sample is equalized to determine the size of the background that affects the fluorescent X-ray intensity due to apparatus factors other than the sample. T The X-ray intensity ratio is calculated using the value obtained by subtracting the ground from the measured value of the fluorescent X-ray intensity of the sample as the fluorescent X-ray intensity, and the calibration curve is obtained using the X-ray intensity ratio. Then, the concentration of the measurement target component in the sample is calculated (claim 1).
Further, the X-ray fluorescence analyzer of the present invention using the background correction method described above is an X-ray detector that measures the fluorescent X-ray intensity and scattered X-ray intensity generated from a sample when the sample is irradiated with X-rays. And the X-ray intensity ratio between the fluorescent X-ray intensity measured by the X-ray detector and the scattered X-ray intensity and the calibration curve obtained using the standard sample, the fluorescent X-ray and scattered X-ray of the sample In the X-ray fluorescence analysis apparatus, the CPU includes a CPU that calculates the concentration of the component to be measured in the sample using the same effect of absorption by the coexisting elements contained in the sample. the fluorescence of the addition, the equal measurement target component concentration, and a plurality of constant density sample coexisting elements are mounted on different Do Ri the fluorescent X-ray analyzer means for calculating process the concentration of the measurement target component in the sample X-ray intensity and scattered X-ray intensity Has a relationship with the background affect these two X-ray intensity, and the measurement of the fluorescent X-ray intensity and the scattered X-ray intensity of each constant density sample to be measured by the X-ray detector in this equation Means for substituting the value and determining the magnitude of the background that affects the fluorescent X-ray intensity due to apparatus factors other than the sample, and subtracting the determined background from the measured value of the fluorescent X-ray intensity of the sample of unknown concentration means as well as means asking you to the calibration curve using the calculated X-ray intensity ratio and the standard sample to calculate the the the unknown concentration the X-ray intensity ratio of the sample value as a fluorescent X-ray intensity of a sample of unknown concentration It is characterized by having a (claim 2).
[0013]
Therefore, by using the above-described background correction method, the influence of the background can be almost certainly removed, so that even a very low concentration sample can be accurately quantitatively analyzed. In addition, since the background can be removed without being affected by the amount of coexisting elements contained in the sample, there is little influence from oil types such as heavy oil, light oil, kerosene, gasoline, and gasoline with alcohol, regardless of the amount of coexisting elements. Accurate quantitative analysis can be performed, and there is no need to create a calibration curve for each oil type.
[0014]
In addition, when calculating the X-ray intensity ratio as a ratio of a value obtained by subtracting the background from a measured value of fluorescent X-ray intensity and a measured value of scattered X-ray intensity, an almost accurate calculation is performed with a simpler calculation. Can be performed.
[0015]
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram illustrating the present invention, and is a partially enlarged view of the fluorescent X-ray analyzer already described in detail with reference to FIG. In the following description, the energy spectrum disclosed in FIGS. 1 and 2 is a schematic diagram for simplifying the description and is not an actual measurement result.
[0017]
As shown in FIG. 1, the X-ray 2 emitted from the X-ray tube 1 has an energy characteristic having a peak at, for example, 4.5 keV. The X-ray 2 is irradiated onto the measurement target sample 3 with a diameter of, for example, 25 mmφ to excite sulfur in the sample 3. The secondary X-ray 4 consisting of the scattered X-ray 4b and the fluorescent X-ray 4s by the sample 3 enters the X-ray detector 5 through the niobium filter F, and is converted into an electric signal. Since the scattered X-ray 4b scatters titanium characteristic X-rays, it has an energy characteristic having a peak in the vicinity of 4.5 keV, and the fluorescent X-ray 4s has an energy characteristic having a peak at sulfur energy 2.3 keV. Have
[0018]
Further, the X-ray 2 is scattered by air A (only one point is shown in FIG. 1 but actually scattered from any position) existing in the irradiation region to generate scattered light 2 ′, and the scattered light. 2 ′ excites the niobium filter F. The X-ray 2f generated by exciting the niobium filter F has an energy characteristic having a peak in the vicinity of energy 2.3 keV which is substantially the same as that of sulfur.
[0019]
Note that the energy characteristic of the scattered light 2 ′ by air has a peak at 4.5 keV, which is the same as that of the X-ray 2, and the background b due to various apparatus factors other than these samples 3 is input to the X-ray detector 5. The On the other hand, the scattered X-ray 4b generates a background a due to the sample 3.
[0020]
Then, the X-ray input to the X-ray detector 5 is separated into a fluorescent X-ray intensity S having an energy of 2.3 keV and a fluorescent X-ray intensity B having an energy of 4.5 keV, and each is measured and processed. .
[0021]
In the background correction method of the fluorescent X-ray analysis apparatus of the present invention, the CPU 8 calculates the more accurate concentration by deriving the background b caused by the apparatus other than the sample 3. That is, instead of the simple X-ray intensity ratio (S / B) based on the fluorescent X-ray intensity S and the scattered X-ray intensity B as in the prior art, this is calculated from the fluorescent X-ray intensity S as shown in the following equation (1). An X-ray intensity ratio R with the scattered X-ray intensity B as the denominator is calculated with respect to the background b subtracted.
R = S−b / B Formula (1)
[0022]
That is, the X-ray intensity ratio R is obtained from the value obtained by subtracting the background b due to apparatus factors other than the sample from the measured value of the fluorescent X-ray intensity S and the scattered X-ray intensity B. In the above formula (1), the calculation is performed assuming that the background size affecting the measured value of the scattered X-ray intensity B having an energy characteristic of 4.5 keV is negligible. However, the present invention is not limited to this point.
[0023]
When performing a more rigorous calculation, the size of the background b is divided into a background b ₁ that affects the fluorescent X-ray intensity S and a background b ₂ that affects the scattered X-ray intensity B. It is also possible to calculate the X-ray intensity ratio as R = (S−b ₁ ) / (B−b ₂ ).
[0024]
Next, a method for deriving the background b will be described with reference to FIG. The derivation of the background is two constant-concentration samples 3d and 3m (in this example, decalin 3d and methanol 3m as an example) where the concentration of the element to be measured is 0 (an example where the concentrations are equal) and the coexisting elements are greatly different. ). In addition, when performing the above-mentioned stricter calculation, the backgrounds b ₁ and b ₂ can be obtained using three constant concentration samples.
[0025]
Both the constant concentration samples 3d and 3m are mounted on a fluorescent X-ray analyzer as the measurement target sample 3 shown in FIG. 1, and the scattered X-ray intensities Bd and Bm and the fluorescent X-ray intensities Sd and Sm are measured in each case. Find the value. The measured values of the X-ray intensities Sd, Bd, Sm, and Bm measured using the two constant concentration samples 3d and 3m as the measurement target sample 3 include the following elements.
[0026]
That is, the measured values of the fluorescent X-ray intensities Sd and Sm (fluorescent X-ray intensity Sd in decalin, fluorescent X-ray intensity Sm in methanol) are irradiated with the fluorescent X-ray intensity and titanium characteristic X-rays due to the fluorescence of the samples 3d and 3m. The background a caused by the sample 3 containing X-rays having energy of 2.3 keV (sulfur characteristic) slightly emitted from the X-ray tube 1 and scattered by the samples 3d and 3m, air scattering, and the niobium filter F It is the sum of background b ₁ (hereinafter referred to as background b) generated by various device factors such as excitation. Here, since both the constant concentration samples 3d and 3m do not contain any component to be measured, the fluorescent X-ray intensity due to the fluorescence of the samples 3d and 3m can be zero.
[0027]
The measured values of the scattered X-ray intensities Bd and Bm (scattered X-ray intensity in decalin Bd and scattered X-ray intensity in methanol Bm) are X-rays of energy 4.5 keV scattered by the samples 3d and 3m, This is the sum of the background b ₂ caused by various device factors such as scattering. Note that the size of the background b ₂ is sufficiently smaller than the X-ray having an energy of 4.5 keV scattered by the samples 3d and 3m, and can be ignored.
[0028]
Therefore, the relationship between the measured values of the X-ray intensities Sd, Bd, Sm, and Bm and the background b can be expressed by the following equation (2). Since the background a is affected by the coexisting elements of the samples 3d and 3m, it is not necessary to subtract in the equation (2).
Sm−b / Bm = Sd−b / Bd (2)
[0029]
Next, depending on the sample 3 by substituting the measured values of the secondary X-ray intensities Sd, Bd, Sm, and Bm measured using the two constant concentration samples 3d and 3m into the above equation (2), It is possible to determine the size of the background b due to device factors that do not. Further, by substituting the background b obtained in this way into the equation (1) to obtain the X-ray intensity ratio R in the sample 3 having an unknown concentration, the X-ray intensity ratio R is included in the sample 3. It can be obtained accurately regardless of the amount of coexisting elements.
[0030]
Here, the background b can be separated not only by the influence of the X-ray 2 'scattered by the air A but also by the system peak caused by the apparatus such as the excitation of the niobium filter F and the limit of the resolution of the detector. It also includes energy that was not measured. Therefore, the present invention obtains the X-ray intensity ratio R by subtracting these backgrounds b due to all apparatus factors other than the sample 3 from the measured value of the X-ray intensity, thereby obtaining the background due to various apparatus factors. The influence of b can be eliminated at all. That is, even when the background b cannot be determined only by measuring one sample 3, the influence can be removed almost completely.
[0031]
Next, FIG. 3 shows an example of a calibration curve C using the X-ray intensity ratio R, and how to find the calibration curve C will be described below. That is, the calibration curve C shown in FIG. 3 measures the fluorescent X-ray intensity S and the scattered X-ray intensity B of the standard sample 3s having a known concentration, and the measured values S and B of the respective X-ray intensities together with the background b that has already been obtained. By substituting into the formula (1), it can be created using the X-ray intensity ratio R.
[0032]
If the calibration curve C can be expressed by, for example, a quadratic curve, the following equation (3) is obtained.
C = α × R ² + β × R + γ
= Α × (S−b / B) ² + β × (S−b / B) + γ (3)
[0033]
In this example, since the calibration curve C is expressed by a quadratic equation, three or more standard samples 3 _{s1 to} 3 _s3 having different known concentrations C ₁ , C ₂ and C 3 are used as the standard sample 3s. X-ray intensity ratios R ₁ , R ₂ , R ₃ can be measured, and the coefficients α, β, γ can be obtained from these. The number of standard samples 3s is 2 or more when the calibration curve C is a linear expression, and 4 or more when the calibration curve C is a cubic expression or more, that is, one more than the order. The coefficient can be obtained using the standard sample 3s.
[0034]
Then, by obtaining the calibration curve C as described above, the concentration Cx can be calculated for the sample 3x having an unknown concentration. As already described in detail, since the same calibration curve C can be used regardless of the amount of coexisting elements contained in the sample 3, it is not necessary to recreate it every time the type of the sample 3 changes. In view of the fact that the size of the background b caused by the apparatus factors changes with time, the calibration can be performed using the constant concentration samples 3d and 3m and the standard sample 3s by the above-described method.
[0035]
[0036]
【The invention's effect】
As described above, according to the present invention, the influence of the background can be almost certainly removed regardless of the amount of coexisting elements and the type of sample, so that even a very low concentration sample can be quantitatively analyzed accurately. In addition, accurate quantitative analysis can be performed even if the oil type such as heavy oil, light oil, kerosene, gasoline, gasoline with alcohol, etc., with different amounts of coexisting elements is changed. In addition, it is not necessary to create a calibration curve for each oil type.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a main part of a fluorescent X-ray analyzer of the present invention.
FIG. 2 is a diagram showing measured values of secondary X-rays from a constant concentration sample.
FIG. 3 is a diagram showing an example of a calibration curve.
FIG. 4 is a diagram showing an overall configuration of a fluorescent X-ray analyzer.
FIG. 5 is a diagram showing measured values of secondary X-rays measured by the X-ray fluorescence analyzer.
FIG. 6 is a diagram showing an example of a conventional calibration curve.
FIG. 7 is a diagram showing measured values of secondary X-rays when a low concentration measurement target sample is measured.
[Explanation of symbols]
2 ... X-ray, 3 ... sample, 3d, 3m ... constant concentration sample, 3s ... standard sample, 5 ... X-ray detector, 8 ... CPU, R ... X-ray intensity ratio, b ... background, B , Bd, Bm ... scattered X-ray intensity, C ... calibration curve, S 1 , Sd, Sm ... fluorescent X-ray intensity.

Claims (3)

Using the X-ray intensity ratio between the fluorescent X-ray intensity measured by the X-ray detector when the sample is irradiated with X-rays and the scattered X-ray intensity, and the calibration curve obtained using the standard sample, Fluorescence X in which the concentration of the measurement target component in the sample is calculated using the fact that both the fluorescent X-ray and the scattered X-ray of the sample are similarly affected by the absorption effect of the coexisting elements contained in the sample. In the line analyzer,
Measure fluorescence X-ray intensity and scattered X-ray intensity of a plurality of constant concentration samples with the same concentration of components to be measured and different coexisting elements, and use the fact that the X-ray intensity ratio of each constant concentration sample is equal. The intensity of the background that affects the fluorescent X-ray intensity due to the factors of the apparatus is obtained, and the X-ray intensity is obtained by subtracting the obtained background from the measured value of the fluorescent X-ray intensity of the sample as the fluorescent X-ray intensity. The background correction of the fluorescent X-ray analyzer characterized by calculating the ratio, obtaining the calibration curve using the X-ray intensity ratio, and calculating the concentration of the component to be measured in the sample using the calibration curve Method. X-ray detector for measuring fluorescent X-ray intensity and scattered X-ray intensity generated from the sample when the sample is irradiated with X-ray, and fluorescent X-ray intensity and scattered X-ray measured by the X-ray detector Using the X-ray intensity ratio with respect to the intensity and the calibration curve obtained using the standard sample, both the fluorescent X-ray and scattered X-ray of the sample are similarly affected by absorption by the coexisting elements contained in the sample. In a fluorescent X-ray analyzer having a CPU that calculates the concentration of the measurement target component in the sample by using
Wherein the CPU, in addition to the means for calculation the concentration of the measurement target component in the sample, equal measurement target component concentration, and a plurality of constant density sample coexisting elements are mounted on different Do Ri the fluorescent X-ray analyzer The relationship between the fluorescent X-ray intensity and scattered X-ray intensity and the background that affects both X-ray intensities, and each constant concentration sample measured by the X-ray detector in this relational expression. Means for substituting the measured values of the fluorescent X-ray intensity and scattered X-ray intensity to determine the size of the background that affects the fluorescent X-ray intensity due to apparatus factors other than the sample , and the calculated background for the unknown concentration means and the calculated X-ray intensity ratio and the standard thereof calculating the X-ray intensity ratio of the sample of the unknown concentration values obtained by subtracting from the measured value of the fluorescent X-ray intensity of the sample as a fluorescent X-ray intensity of a sample of unknown concentration X-ray fluorescence spectrometer, characterized in that a means asking you to the calibration curve using the fee.   The X-ray fluorescence analyzer according to claim 2, wherein the component to be measured is sulfur contained in petroleum.

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