JP7153324B2 - Elemental analysis method - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Law Guide to the 78th Conference on Analytical Chemistry [Publications] Program of the 78th Conference on Analytical Chemistry (Partial) [Publications, etc.] Copy of the 78th Conference on Analytical Chemistry (B1002) [Publications, etc.] Guide to ICONE26

The present invention relates to an elemental analysis method and an elemental analysis apparatus using an electron probe microanalyzer (EPMA).

2. Description of the Related Art An electron probe microanalyzer (EPMA) is widely used to analyze elements in a sample by irradiating the sample with an electron beam in a vacuum and examining fluorescent X-rays (characteristic X-rays) emitted from the sample. In this case, since it is easy to use together with an electron beam microscope (SEM), it is possible to easily investigate (mapping) the distribution of a specific element on the sample surface.

In this case, the intensity (number of counts) for each energy (or wavelength) of X-rays emitted from the sample irradiated with the electron beam is recognized by the X-ray detector, and the X-ray spectrum (vertical axis: intensity (number of counts) , horizontal axis: wavelength). In this X-ray spectrum, since the position (wavelength) of the characteristic X-ray peak corresponding to each element is known in advance, the composition (ratio) of each element can be determined by recognizing the intensity of the peak corresponding to each element. can be calculated. For example, Patent Literature 1 describes a technique for analyzing the composition of oxygen in metal materials by EPMA. In this case, in the X-ray spectrum, the peak of the characteristic X-ray of the metal element (K _β line of Al: around 0.8 nm wavelength) and the peak of the characteristic X-ray of oxygen (K _α line of O: around 2.36 nm wavelength) are far apart on the horizontal axis (the X-ray energies or wavelengths are significantly different), the composition of metal elements and oxygen can be easily calculated.

JP 2014-228307 A

In general, a single element emits characteristic X-rays at multiple wavelengths. Therefore, in EPMA, when there are a plurality of elements to be measured, the number of peaks corresponding to the characteristic X-rays emitted from each element increases in the X-ray spectrum. Among these, if the peak corresponding to the characteristic X-ray of a certain element and the peak corresponding to the characteristic X-ray of another element exist at positions separated from each other on the horizontal axis, the intensity of each peak can be recognized, The composition of each element can be recognized from the intensity of each peak. However, in practice, when the positions of the peaks corresponding to the characteristic X-rays of the two elements are close to each other on the horizontal axis, these peaks may overlap depending on the wavelength resolution of the measurement. In some cases, the intensity could not be recognized accurately.

For example, zirconium (Zr), boron (B), and oxygen (O) are mixed in fuel debris and various ceramic materials to be handled in the decommissioning of nuclear reactors. The physical properties such as hardness are greatly different. Therefore, composition analysis of Zr and B is important in these materials. However, the peak of the strongest characteristic X-ray of B (K _α1 line of B: around 6.8 nm wavelength) and the peak of the characteristic X-ray of Zr (M _z line of Zr: around 6.9 nm wavelength) are close to each other. Therefore, it was difficult to accurately calculate the composition of B by EPMA in the presence of Zr.

Therefore, when the peak corresponding to the characteristic X-ray of the element to be measured interferes with the peak corresponding to the characteristic X-ray of the interfering element in the X-ray spectrum obtained by EPMA, the composition of the element to be measured can be calculated with high accuracy. was asked to do so.

The present invention has been made in view of such problems, and an object of the present invention is to provide an invention that solves the above problems.

In order to solve the above problems, the present invention has the following configurations.
In the elemental analysis method of the present invention, in the X-ray spectrum obtained when an electron beam is irradiated with an electron probe microanalyzer (EPMA), the characteristic X-ray peak emitted by the element to be measured interferes with the measurement target peak. An elemental analysis method for calculating the composition of the element to be measured at a measurement point in a sample by measuring the intensity of the peak to be measured in the presence of an interfering element that emits characteristic X-rays, wherein at the measurement point, the a correction intensity measuring step of measuring a correction intensity, which is an X-ray intensity of a reference wavelength corresponding to a characteristic X-ray emitted by an interfering element that does not interfere with the peak to be measured; At the point, a measurement target element measurement step of measuring the measured intensity, which is the X-ray intensity of the wavelength corresponding to the measurement target peak, and the corrected intensity obtained by subtracting the value obtained by multiplying the correction intensity by a correction coefficient from the measured intensity. and a correcting step of recognizing the composition of the element to be measured more accurately , wherein the interfering element is contained in a portion of the sample that does not overlap with the measurement point in the region irradiated with the electron beam, and the measurement target A first intensity for correction coefficient calculation, which is an X-ray intensity of a wavelength corresponding to the peak to be measured when a standard region containing no element is set and the standard region is irradiated with the electron beam; a second intensity for calculating a correction coefficient, which is an X-ray intensity at a wavelength; The value obtained by dividing by is used as the correction coefficient, and the portion that becomes the standard region is given to the sample .
The elemental analysis method of the present invention is characterized by comprising a display step of setting a plurality of measurement points on the sample, and mapping and displaying the corrected intensity at each of the measurement points.
In the elemental analysis method of the present invention, the element to be measured is boron (B), and the interfering element is a metal element.
The elemental analysis method of the present invention is characterized in that the metal element is zirconium (Zr) .

Since the present invention is configured as described above, when the peak corresponding to the characteristic X-ray of the element to be measured interferes with the peak corresponding to the characteristic X-ray of the interfering element in the X-ray spectrum obtained by EPMA, The composition of the element to be measured can be calculated with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structure of the elemental-analysis apparatus used for the elemental-analysis method based on embodiment of this invention. 1 shows (a) a backscattered electron image of a sample, (b) the mapping result of the characteristic X-ray intensity of B, and (c) the mapping result of the characteristic X-ray intensity of Zr in a conventional elemental analysis method using EPMA. It is a diagram. FIG. 4 is a diagram showing the state of an X-ray spectrum when the _Mz line of Zr (wavelength: 6.9 nm) exists in the vicinity of the K _α1 line of B (wavelength: 6.8 nm). It is a figure explaining typically the X-ray spectrum recognized in the elemental-analysis method based on embodiment of this invention. It is a mapping result of the post-correction intensity of B obtained by the elemental analysis method according to the embodiment of the present invention. It is the result of examining the correspondence between the intensity after correction of B obtained by the elemental analysis method according to the embodiment of the present invention and the B composition of the sample.

FIG. 1 shows the configuration of an elemental analysis apparatus 1 that performs an elemental analysis method according to an embodiment of the present invention. The configuration shown in FIG. 1 is common to an analyzer using a commonly known EPMA, particularly a WDS (Wavelength Dispersive Spectrometer).

Here, an electron beam 100 emitted from an electron source 10 is irradiated onto a desired portion of the sample S via an optical system 20 . At this time, each atom constituting the sample S is excited by the electrons in the electron beam 100, and then emits characteristic X-rays determined for each type of atom (element). Therefore, the X-rays 200 emitted from the surface of the sample S contain all the characteristic X-rays emitted by each element contained in the sample S, and the X-rays 200 are spectroscopically separated by the condensing spectroscopic element 30. of X-rays 210 are detected by the X-ray detector 40 . The condensing spectroscopic element 30 and the X-ray detector 40 are movable and rotatable around the sample S in a state of being on the Rowland circle R. The angle of incidence on 30 varies. As a result, the energy (or wavelength) of the X-rays detected by the X-ray detector 40 is appropriately changed, and the X-ray spectrum, which is the detected intensity for each energy or wavelength of the X-rays 200, is obtained in the X-ray detector 40. be able to. In the X-ray spectrum, the horizontal axis is the X-ray energy or wavelength, and the vertical axis is the detected intensity (count number in the X-ray detector 40) at this X-ray energy or wavelength. explain.

At this time, the wavelength of the X-ray is determined in advance, the condensing spectroscopic element 30 and the X-ray detector 40 are fixed in a corresponding positional relationship, and the sample S is moved to adjust the irradiation position of the electron beam 100 on the sample S. By varying the X-ray intensity at this wavelength can be mapped onto the sample S. By using this wavelength as the wavelength of the characteristic X-ray emitted by the element to be analyzed, the distribution of this element in the sample S can be recognized.

In order to obtain the detection intensity (X-ray spectrum) for each wavelength with the X-ray detector 40 in this manner, the condensing spectroscopic element 30 is used as described above, and moves and rotates together with the X-ray detector 40. It is set to If an X-ray spectrum can be obtained with sufficient wavelength resolution (energy resolution) by directly detecting the X-rays 200 with the X-ray detector 40, a method other than WDS as described above may be used. In this case, the condensing spectroscopic element 30 is unnecessary, and the position of the X-ray detector 40 can be fixed and used.

The analysis unit 50 is, for example, a personal computer, obtains this X-ray spectrum, and analyzes the composition of the elements contained in the sample S. FIG. Also, the analysis unit 50 is connected to a storage unit 60 that stores various data used when performing this analysis. The analysis unit 50 also controls the movement and rotation of the condensing spectroscopic element 30 and the X-ray detector 40 as described above.

A display unit 70 capable of displaying a two-dimensional image is used to display the mapping result of the X-ray intensity (composition of a specific element) as described above.

The elemental analysis apparatus 1 is also provided with an electron detector 80 for detecting electrons (backscattered electrons 220) generated from the sample S side by being irradiated with the electron beam 100. FIG. As a result, the analysis unit 50 can also obtain a backscattered electron image of the sample S, which is the backscattered electron mapping result, and display this on the display unit 70 in the same manner as in the mapping of the elements described above.

First, the result of using the conventional elemental analysis method using the configuration of FIG. 1 will be described. Here, as the sample S, a fuel debris of a nuclear reactor or a simulated sample assumed to be fuel debris is used. In this case, the element to be measured is boron (B), and zirconium (Zr), which is a metal element, is included as one of the main components, and B is segregated therein. Therefore, mapping of the detected intensity at a wavelength of 6.8 nm corresponding to the characteristic X-ray with the highest intensity of B (K _α1 line of B) in the obtained X-ray spectrum was performed as described above.

FIG. 2A is a backscattered electron image of the sample S obtained as described above, and FIG. is. On the other hand, FIG. 2(c) is a similar mapping result of the characteristic X-ray ( _Lα line: wavelength 0.61 nm) of Zr, which is the main component of the sample S. As shown in FIG.

In this sample S, it is clear that there is a correlation between the backscattered electron image (Fig. 2(a)) that mainly reflects the surface shape of the sample S and the distribution of Zr, which is the main component (Fig. 2(c)). Therefore, the results in FIGS. 2(a) and 2(c) are similar. On the other hand, since B is segregated in sample S, the distribution of Zr and the distribution of B do not match, but the results in FIGS. 2(b) and 2(c) are similar.

This is due to the presence of a large amount of Zr M _z line (wavelength 6.9 nm) in the vicinity of the B K _α1 line (wavelength 6.8 nm) used in the measurement of FIG. However, in the measurement of FIG. 2(b), the influence of the _Mz line of Zr exists at the same time. FIG. 3 shows the result of measuring the X-ray spectrum in the vicinity of this wavelength for the sample S, whose composition is determined in advance as BN, Zr (cladding tube), and ZrO ₂ (simulated pellet). The BN measurement results show a B K _α1 peak, and the Zr and ZrO ₂ measurement results show a Zr M _z -line peak centered at a wavelength of 6.9 nm. Since the peak of each characteristic X-ray detected by the X-ray detector 40 has a spread, the tail of the peak of the Zr _Mz line overlaps with the peak of the B _Kα1 line. Therefore, in the measurement result of B (FIG. 2(b)), the influence of Zr exists to such an extent that it cannot be ignored.

Here, in the case where an element (interfering element: Zr in the above example) that emits a characteristic X-ray having a wavelength close to that of the element to be measured (B in the above example) is mixed in the sample S, this In the elemental analysis method according to the embodiment, the composition of the element to be measured can be obtained by reducing the influence of interfering elements by the technique described below. This processing is performed by the analysis unit 50 .

Here, the analysis unit 50 measures the intensity of one peak of characteristic X- _rays emitted by B as shown in FIG. (measurement target element measurement step). In the intensity measured here (measured intensity), as described above, the intensity due to the M _z line of Zr (interfering element) with respect to the intensity due to the K _α1 line of B, that is, the M The intensity of the tail of the _z -line peak is superimposed, and the intensity of the latter is not negligible with respect to the intensity of the former.

For this reason, the analysis unit 50 determines the wavelength (reference wavelength) is set, and the intensity (correction intensity) at this reference wavelength at the above measurement point is measured by moving the condensing spectroscopic element 30 and the X-ray detector 40 as described above, and the X-ray detector 40 (correction intensity measurement step). Either the measurement target element measurement process or the correction intensity measurement process may be performed first. After that, the intensity after correction is calculated by correcting the actually measured intensity using the correction intensity, and the composition of the element to be measured is recognized from the intensity after correction (correction step). Further, for example, when mapping the measurement target element, the measurement target element measurement process is performed at all the measurement points, the results are stored in the storage unit 60, and the correction intensity measurement process is similarly performed at all the measurement points. The result may be stored in the storage unit 60, and the post-correction intensity may be calculated for each measurement point as a final correction step.

The upper part of FIG. 4 is a diagram schematically showing an X-ray spectrum at a measurement point recognized by the X-ray detector 40 in the process of measuring the element to be measured and the process of measuring the intensity for correction. Here, peaks related to detected intensities are shown schematically. First, around the wavelength λ ₁ corresponding to the peak to be measured (K _α1 line of B), there is a peak to be measured P ₁₁ having a peak intensity of I ₁₁ , and the intensity at the wavelength λ ₁ of the peak to be measured P ₁₁ is the peak Consistent with intensity I ₁₁ . _On the other hand, a peak (interference peak) P21 of the M _z -line of Zr having a peak intensity _I21 exists in the vicinity of this measurement target peak _P11 . _In the interference peak P21, the peak is obtained on the larger wavelength _side than λ1, so the measured peak _P11 and the interference peak _P21 partially overlap. However, since the peak intensity _I21 is large, the intensity _I211 at the foot of the interference peak _P21 at the wavelength λ1 is _a value that cannot be ignored compared to _I11 . The actual peak in the X-ray spectrum actually detected by the X-ray detector 40 in the process of measuring the element to be measured becomes the measured peak _P31 in which the above-mentioned peak to be measured _P11 and the interference peak _P21 are superimposed. b) is the mapping result of the peak intensity (measured intensity) _I31 of this measured peak _P31 . Here, the measured intensity I ₃₁ can be approximated by I ₁₁ +I ₂₁₁ . Here, it is necessary to obtain I ₁₁ corresponding only to the B composition, but what is actually measured is the above I ₃₁ , and in order to calculate I ₁₁ , it is necessary to recognize I ₂₁₁ .

On the other hand, in the correction intensity measurement step, among the peaks of the characteristic X-rays emitted by Zr (interfering element), the wavelength corresponding to the peak that does not interfere with the peak of the characteristic X-rays emitted by B (the element to be measured) is chosen as the reference wavelength above. In the upper part of FIG. 4, 0.61 nm, which is the wavelength corresponding to the peak of the L _α line of Zr (reference peak), is set as the reference wavelength λ ₂ . Around the reference wavelength λ ₂ , there is only the reference peak P ₄₁ of the peak intensity I ₄₁ due to Zr, so that the intensity at the wavelength λ ₂ of the reference peak P ₄₁ coincides with the peak intensity I ₄₁ λ ₂ is defined. This peak intensity I41 is the correction intensity detected by the X-ray detector ₄₀ in the correction intensity measurement step.

On the other hand, the lower part of _FIG . 4 shows the same measurement as the upper part of FIG. The X-ray spectrum in the case of performing the correction data acquisition step) is shown. Here, the first peak _P20 , which is the peak of the Zr _Mz line corresponding to the interference peak _P21 , and the second peak, which is the peak of the Zr L _α line, corresponding to the reference peak _P41 The peak intensity of the former is I ₂₀ and the peak intensity of the _{latter is I 40 .} As described above, when the B composition in the standard sample is negligible, and the effect of the characteristic X-rays of elements other than B on the _second peak _P40 is negligible, _I40 is X-ray detection at wavelength λ2 equal to the detection intensity of the device 40. Further, when the influence of the characteristic X-rays of elements other than B on the first peak _P20 can be ignored, the intensity corresponding to the intensity _I211 of the tail of the interference peak _P21 is the first peak The intensity I ₂₀₁ of the tail of P ₂₀ is measured at wavelength λ ₁ .

In this case, the ratio of the intensity (tail intensity) at the wavelength λ ₁ and the peak intensity at the peak of the M _z line of Zr is I ₂₁₁ /I ₂₁ at the measurement point and I ₂₀₁ /I ₂₀ at the standard sample. but they are considered equal. Also, the peak intensity ratios of different characteristic X-rays (M _z ray, L _α ray) emitted by Zr are I ₄₁ /I ₂₁ at the measurement point and I ₄₀ /I ₂₀ at the standard sample, which are also considered to be equal. For this reason, I ₁₁ (intensity after correction) that reflects only the B composition at the measurement point is obtained by subtracting the value obtained by multiplying the corrected intensity I ₄₁ by the correction coefficient C from the measured intensity I ₃₁ , using the following formula (1): The correction coefficient C in this is I ₂₀₁ (first intensity for correction coefficient calculation) and I ₄₀ (correction coefficient calculation (2) using the second intensity).

When performing measurements at a _plurality of measurement points as described above, it is necessary to _measure I ₃₁ and I ₄₁ at each measurement point. It is only necessary to perform this only once, and when calculating I11 at each measurement point by the correction according to the formula ( ₁ ), it is sufficient to use C common to all measurement points. Furthermore, it is not necessary to calculate C for each sample S (perform the correction data acquisition step), and the value of C obtained in advance may be stored in the storage unit 60 and used in all measurements. After that, the corrected intensity I11 calculated at each measurement point can be displayed as a two-dimensional distribution on the display unit 70 in the same manner as in FIG. 2B and the like (display step). FIG. ₅ shows the mapping result of I11 calculated using C of a constant value (=0.51) determined in this way. In this result, since the influence of Zr is eliminated, a local distribution of B appears unlike the Zr mapping result (FIG. 2(c)).

That is, by the above elemental analysis method, in the X-ray spectrum used in EPMA, the peak corresponding to the characteristic X-ray of the element to be measured (B) and the peak corresponding to the characteristic X-ray of the interfering element (Zr) are close to each other. In this case, the composition of the element (B) to be measured can be calculated with high accuracy.

In the above example, the composition of the element to be measured (the peak intensity of the peak to be measured) is mapped. , the above elemental analysis method can be applied. In this case, a calibration curve is prepared by examining the I ₁₁ (intensity after correction) calculated by the above method for a plurality of samples S for which the composition of the element to be measured is known in advance, and this is used for the subsequent measurement. can be used in

FIG. 6 shows the relationship between the B composition and the corrected intensity I11 for a plurality of samples in which the B composition is known in advance by LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry). It is the result (calibration curve) of the examination. From this result, there is a linear relationship between the corrected intensity and the B composition, and this makes it possible to convert the corrected intensity to the B composition.

In the above example, B is the element to be measured and Zr is the interfering element. Similarly, in the X-ray spectrum recognized by the X-ray detector, The above-described elemental analysis method is effective when an interfering element that emits characteristic X-rays is present at the same time as the element to be measured. That is, the above elemental analysis method can be similarly applied even if the above-mentioned measurement target element and interference element are other than the above examples.

In the above example, the elemental analyzer having the configuration shown in FIG. 1 was used, but the spread (energy or wavelength resolution) of the characteristic X-ray peak in the recognized X-ray spectrum depends on this measuring apparatus. do. At this time, when an element to be measured is determined, an element that does not become the above-mentioned interfering element when the energy (wavelength) resolution is high becomes an interfering element in another apparatus with low energy (wavelength) resolution. In some cases. That is, the interfering element is set according to the configuration of the apparatus when the element to be measured is determined.

In the above example, one interfering element (Zr) was set for one element to be measured (B), but in some cases, a plurality of interfering elements exist (in the upper part of FIG. 4, a plurality of interference peaks exists). In such a case, the above correction intensity measurement step is performed for each interfering element, the measurement (correction coefficient setting) in the lower part of FIG. The value obtained by multiplying the correction intensity of each interfering element by the correction coefficient may be accumulated and subtracted from.

In the above example, the sample S is assumed to be fuel debris or a simulated sample related thereto, but it is clear that the above elemental analysis method can be applied to other substances as well. In particular, the above composition analysis method is similarly effective for metal materials and ceramic materials in which metal elements (Zr, Fe, etc.) and O and B are mixed, in addition to fuel debris. At this time, if a metal precipitate is present, this precipitate can be used as the standard sample. Therefore, even when performing the above correction data acquisition step, if there is such a region (standard region) that can be used as a standard sample, it is not necessary to newly provide a standard sample.

1 Elemental analyzer 10 Electron source 20 Optical system 30 Condensing spectroscopic element 40 X-ray detector 50 Analysis part 60 Storage part 70 Display part 80 Electron detector 100 Electron beams 200, 210 X-rays 220 Backscattered electrons P ₁₁ peak to be measured _P21 Interference peak _P31 Measured peak _P41 Reference peak _P20 First peak _P40 Second peak R Rowland circle S Sample

Claims (4)

In the X-ray spectrum obtained when an electron beam is irradiated with an electron probe microanalyzer (EPMA), there is an interfering element that emits characteristic X-rays that interfere with the measurement target peak, which is the peak of the characteristic X-rays emitted by the measurement target element. An elemental analysis method for calculating the composition of the element to be measured at the measurement point in the sample by measuring the intensity of the peak to be measured in the presence of
At the measurement point, the correction intensity for measuring the X-ray intensity of the reference wavelength corresponding to the characteristic X-rays emitted by the interfering element that do not interfere with the peak to be measured. a measuring step;
a measurement target element measuring step of measuring, at the measurement point, an actually measured intensity, which is an X-ray intensity of a wavelength corresponding to the measurement target peak;
a correction step of recognizing the composition of the element to be measured from the corrected intensity obtained by subtracting the value obtained by multiplying the correction intensity by a correction coefficient from the measured intensity;
and
A standard region containing the interfering element and not containing the element to be measured is set at a location that does not overlap with the measurement point in the region irradiated with the electron beam in the sample,
A first intensity for correction coefficient calculation, which is the X-ray intensity of the wavelength corresponding to the peak to be measured when the standard region is irradiated with the electron beam, and a correction coefficient calculation, which is the X-ray intensity at the reference wavelength a correction data acquisition step for measuring a second intensity for
In the correcting step, a value obtained by dividing the first strength for calculating the correction coefficient by the second strength for calculating the correction coefficient is defined as the correction coefficient;
A method of elemental analysis, characterized in that a portion to be the standard region is given to the sample . A plurality of the measurement points are set on the sample,
2. The elemental analysis method according to claim 1 , further comprising a display step of mapping and displaying the post-correction intensity at each of the measurement points. 3. The elemental analysis method according to claim 1, wherein the element to be measured is boron (B), and the interfering element is a metal element. 4. The elemental analysis method according to claim 3 , wherein said metal element is zirconium (Zr).

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