JP2004170143A - X-ray analysis method and X-ray analyzer - Google Patents

Abstract

An object of the present invention is to remove the influence of electrical noise in X-ray analysis using low-energy characteristic X-rays.
In an X-ray analysis using low-energy characteristic X-rays, a detection signal including a low-energy characteristic X-ray and a noise component and a detection signal including only a noise component are obtained, and the low-energy characteristic X-ray is obtained. By subtracting the detection signal of only the noise component from the detection signal including the noise component, a signal from which the influence of the electrical noise is removed is obtained. A first measuring step of measuring characteristic X-rays in a vacuum state on an optical path between the analysis sample and the X-ray detector; and a second measuring step of measuring residual characteristic X-rays absorbing low energy X-rays on the optical path. And a calculation step of subtracting the signal counted in the second measurement step from the signal counted in the first measurement step.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an X-ray analysis method and an X-ray analysis apparatus applied to a fluorescent X-ray analyzer, an EPMA (Electron Probe Microanalyzer), and the like.
[0002]
[Prior art]
Qualitative analysis that irradiates a substance with X-rays, γ-rays, electron beams, etc., measures characteristic X-rays (fluorescent X-rays) emitted from the substance, and analyzes the elements that make up the substance, and the presence of elements X-ray analysis for quantitative analysis to determine the amount, qualitative / quantitative measurement of elements in the sample surface layer, and X-ray analysis such as EPMA (electronic probe / microanalyzer) for secondary analysis of element concentration and state analysis are known. ing.
[0003]
In EPMA, electrons emitted from an electron gun are irradiated on the sample surface, and in X-ray fluorescence analysis, X-rays emitted from an X-ray source are irradiated on the sample surface. When electrons or X-rays accelerated by a high voltage irradiate the sample surface, the inner electrons of the atoms of the sample substance element are excited by the energy of the incident electrons and X-rays and are ejected to the outer shell. At this time, the electrons in the outer shell fall, and the energy corresponding to the energy difference between the electrons in the outer shell and the electrons in the inner shell is emitted as characteristic X-rays. Since this value has a value specific to the element, the emitted X-ray also has a specific wavelength and energy. By measuring the wavelength or energy and the intensity of the characteristic X-ray, qualitative and quantitative determination of the elements of the sample surface material can be performed.
[0004]
In these X-ray analyses, for example, an energy dispersive (ED) X-ray detector using a semiconductor detector is used to measure characteristic X-rays. The semiconductor detector is cooled by a dewar containing liquid nitrogen connected via cold fingers to improve detection performance. After the characteristic X-rays detected by the semiconductor detector are amplified by a proportional amplifier for the pulse signal for each element, the energy of all elements is selected by a multi-channel wave height sorter, and the spectrum is simultaneously displayed on the display device as the characteristic X-rays. indicate.
[0005]
The semiconductor detector is vulnerable to electric noise from disturbance, and if this electric noise is superimposed on an electric signal processing circuit, it will hinder the analysis of the characteristic X-ray. As one cause of the electric noise, there is an electric motor that drives a collimator that limits the amount of incident characteristic X-rays. A technology that suppresses the generation of the electric noise itself by using air pressure instead of the electric motor has been proposed. For example, it is disclosed in Patent Document 1.
[0006]
[Patent Document 1]
JP 2001-43822 A (FIG. 3)
[0007]
[Problems to be solved by the invention]
Examples of the electrical noise detected by the detector include an X-ray source, an exhaust pump, the detector itself, an amplifier, and the like in addition to the electric motor that is a driving source of the collimator. The above-mentioned method cannot deal with dynamic noise.
[0008]
FIG. 6 is a spectrum characteristic diagram for explaining a detection signal due to superposition of electrical noise. FIG. 6A shows a spectrum characteristic A of a sample containing no electrical noise and a spectrum characteristic B of the electrical noise. Here, the spectrum characteristic A of the sample is an ideal state in which electric noise is not included, and a signal actually detected from the detector is formed by removing electric noise as shown in FIG. It is detected as the included spectrum characteristic C. The spectral characteristic B of the electrical noise has a strong signal strength in a region where the peak value is low, as indicated by a broken line in FIG. Therefore, in the spectrum characteristic C including the electric noise, the signal intensity in the region where the peak value is low is a signal in which the electric noise is superimposed on the peak specific to the element, and the peak specific to the element is detected only from the signal intensity. It becomes difficult.
[0009]
Regarding the electrical noise detected by the detector, the peak value of the detected pulse signal is selected by using a peak height discriminator (PHA) to select a signal having a certain height or higher, or an electric gate such as a filter (low level limiter) is used. In general, a signal below a certain level is excluded as noise, and a signal below this level is not counted as noise.
[0010]
However, in the noise removal using such a filter, the S / N ratio (signal-to-noise ratio) is deteriorated, and an erroneous signal may be formed.
[0011]
FIG. 7 is a diagram for explaining electric noise removal by an electric filter. In FIG. 7A, a dashed line D indicates a filter characteristic, a signal in a low peak value region is cut, and a signal in a high peak value region is passed. With this filter characteristic, electrical noise having a strong signal strength in a region where the peak value is low is suppressed.
[0012]
FIG. 7B shows a spectrum characteristic E (broken line in FIG. 7B) obtained by removing electric noise with an electric filter. Comparing the spectral characteristic E (broken line in FIG. 7B) obtained by the electric filter with the ideal spectral characteristic A of the sample (solid line in FIG. 7B), the spectral characteristic E is inherent. Since a peak occurs at a position deviated from the power peak value, and the signal intensity also changes, accurate qualitative analysis / quantification becomes difficult.
[0013]
In addition, the electrical noise included in the signal input to the pulse height discriminator is not always constant, and the total amount of characteristic X-rays generated varies depending on the sample to be analyzed. Is also changed. In particular, in the case of the energy dispersing method using one detector, the influence becomes large.
[0014]
As described above, in quantitative / qualitative analysis using characteristic X-rays, particularly low-energy characteristic X-rays, it is required to remove the influence of electrical noise and extract a signal of a light element.
[0015]
Therefore, an object of the present invention is to solve the above-mentioned conventional problems and to eliminate the influence of electric noise in X-ray analysis using low-energy characteristic X-rays.
[0016]
[Means for Solving the Problems]
According to the present invention, in an X-ray analysis using a low-energy characteristic X-ray, a detection signal including a low-energy characteristic X-ray and a noise component and a detection signal including only a noise component are obtained, and the low-energy characteristic X-ray is obtained. And subtracting the detection signal of only the noise component from the detection signal including the noise component to obtain a signal from which the influence of electrical noise has been removed. Here, the low-energy characteristic X-rays are generated from light elements such as carbon (C) and boron (B).
[0017]
The X-ray analysis according to the present invention can be implemented by a method and an apparatus.
[0018]
An aspect according to the method of the present invention is an X-ray analysis method for counting characteristic X-rays having low energy, wherein a first measurement for measuring characteristic X-rays in a vacuum state on an optical path between an analysis sample and an X-ray detector is performed. A second measuring step of measuring the remaining characteristic X-rays that have absorbed low-energy X-rays on the optical path; and subtracting the signal counted in the second measuring step from the signal counted in the first measuring step. Calculation step.
[0019]
In the first measurement step, since the optical path between the analysis sample and the X-ray detector is in a vacuum state, a noise component is superimposed on a low-energy characteristic X-ray in a signal obtained by the X-ray detector. I have. On the other hand, in the second measurement step, low-energy X-rays are absorbed on the optical path, so that the low-energy region of the signal obtained by the X-ray detector includes only noise.
[0020]
Therefore, in the calculation step, the noise component obtained by counting in the second measurement process is subtracted from the signal in which the noise component is superimposed on the low-energy characteristic X-ray obtained by counting in the first measurement process. An energy characteristic X-ray signal can be obtained.
[0021]
The low-energy X-ray absorption on the optical path performed in the second measurement step can take a plurality of forms. In the first mode, the optical path is in an atmospheric state. When low-energy characteristic X-rays and noise are superimposed and passed through the atmosphere, the low-energy characteristic X-rays are absorbed by heavy elements contained in the atmosphere. Will be reached.
[0022]
In the second mode, the optical path is in a gas state of heavy elements. Here, the heavy element is a heavy element that can sufficiently attenuate low-energy characteristic X-rays such as carbon and boron, and can be, for example, nitrogen gas or carbon dioxide gas. When low-energy characteristic X-rays are passed through a heavy element gas, the low-energy characteristic X-rays are absorbed by the heavy elements contained in the gas, and in the low-energy region, only electrical noise is detected by the X-ray detector. Is output.
[0023]
In the third mode, a filter that absorbs at least low-energy X-rays is arranged on the optical path. As the filter, for example, a polymer filter, beryllium foil or aluminum foil, or a polymer filter obtained by evaporating aluminum or the like can be used. When a low-energy characteristic X-ray and a noise component are superimposed and passed through a filter, the low-energy characteristic X-ray is absorbed by heavy elements contained in the filter, and does not reach the X-ray detector in the low-energy region. Only the electrical noise is output from the X-ray detector.
[0024]
Further, a first apparatus mode of the embodiment according to the apparatus of the present invention is an X-ray analyzer for counting characteristic X-rays of low energy, a probe source for emitting characteristic X-rays to a sample, and an X-ray for detecting characteristic X-rays. A configuration is provided that includes a line detector and a calculation unit that performs a calculation of subtracting a measurement signal of only a noise component from a measurement signal including a characteristic X-ray and a noise component measured by the X-ray detector, respectively.
[0025]
Here, the probe source can be an X-ray source or an electron source, and the primary X-ray emitted from the X-ray source or the electron beam emitted from the electron source is irradiated on the analysis sample, so that the analysis sample can be obtained. Emits characteristic X-rays of energy specific to the element.
[0026]
In the first device mode, the first measurement step and the second measurement step are performed by an X-ray detector, and a measurement signal including low-energy characteristic X-rays and a noise component, and a measurement signal including only a noise component are performed. A signal is obtained, and a low-energy characteristic X-ray is obtained by subtracting the measurement signal containing only the noise component from the measurement signal containing the low-energy characteristic X-ray and noise component by the arithmetic means.
[0027]
According to a second aspect of the present invention, there is provided an X-ray analyzer for counting characteristic X-rays with low energy, a probe source for emitting characteristic X-rays to a sample, and an X-ray detector for detecting characteristic X-rays. And a filter for absorbing low energy X-rays.
[0028]
Here, the filter is configured to be freely put in and out of the optical path of the characteristic X-ray detected by the X-ray detector. With this configuration, when measurement is performed with the filter removed from the optical path, a measurement signal including low-energy characteristic X-rays and noise components is obtained. On the other hand, when the measurement is performed in a state where the filter is arranged on the optical path, a low-energy characteristic X-ray is absorbed by the filter, so that a measurement signal including only noise is obtained.
[0029]
Low-energy characteristic X-rays that do not include noise components remove noise components by subtracting the measurement signal measured with the filter disposed on the optical path from the measurement signal measured with the filter removed from the optical path. Low-energy characteristic X-rays can be obtained.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0031]
FIG. 1 is a schematic diagram for explaining one configuration example of the X-ray analyzer of the present invention. In the configuration example shown in FIG. 1, an X-ray fluorescence analyzer that irradiates an analysis sample with primary X-rays to detect characteristic X-rays (fluorescent X-rays) is taken as an example. EPMA for detecting characteristic X-rays.
[0032]
In FIG. 1, an X-ray analyzer 1 includes an X-ray tube 2 and an X-ray detector 3 in a container 4, and irradiates primary X-rays emitted from the X-ray tube 2 to an analysis sample 10 arranged in the container 4. To generate characteristic X-rays, which are detected by the X-ray detector 3. A pulse signal for each element detected by the X-ray detector 3 is amplified by a proportional amplifier 7 and then discriminated by a peak value discriminator 8 such as a multi-channel pulse height discriminator 8 based on the peak values (energy) of all the elements. And the spectrum of the characteristic X-ray is displayed on the display device 9. As the X-ray detector 3, for example, a lithium drift type semiconductor detector can be used.
[0033]
Further, the container 4 is provided with a vacuum pump 5 and a leak valve 6, and the inside of the container 4 can be evacuated by evacuation, or the air can be brought to an atmospheric state by opening the leak valve 6. By providing a gas source and a valve (not shown), the inside of the container 4 can be brought into a specific gas state. The gas source sufficiently attenuates the characteristic X-rays of the target element (for example, carbon (C) or boron (B)) to be analyzed and used by the X-ray analyzer of the present invention, such as nitrogen gas or carbon dioxide. Gas.
[0034]
The analysis procedure by the X-ray analyzer shown in FIG. 1 will be described with reference to the flowchart shown in FIG. FIG. 3 is a spectrum characteristic diagram obtained by the X-ray analyzer.
[0035]
First, the analysis sample 10 is introduced and arranged in the container 4 (step S1), and the primary X-ray is irradiated from the X-ray source 2 to the analysis sample 10 while keeping the inside of the container 4 in the air state, and emitted from the analysis sample 10. The obtained characteristic X-ray is detected by the X-ray detector 3. At this time, since the space between the analysis sample 10 and the X-ray detector 3 is in the atmospheric state, low-energy characteristic X-rays are absorbed by gas molecules of heavy elements contained in the atmosphere. Therefore, the X-ray detector 3 outputs only the influence of electric noise generated from the X-ray source 2, the X-ray detector 3, and the like. The proportional amplifier 7 and the wave height discriminator 8 perform signal processing on the signal detected by the X-ray detector 3 to obtain a spectral characteristic. FIG. 3A schematically shows the spectrum characteristic B obtained at this time, and includes a noise component at a low energy and a characteristic X-ray at a high energy region (step S2).
[0036]
Next, the inside of the container 4 is evacuated by the vacuum pump 5 to a vacuum state (step S3), and the analysis sample 10 is irradiated with primary X-rays from the X-ray source 2 in the vacuum state of the container 4 and released from the analysis sample 10. The detected characteristic X-rays are detected by the X-ray detector 3. At this time, since the space between the analysis sample 10 and the X-ray detector 3 is in a vacuum state, characteristic X-rays are not absorbed. Therefore, the X-ray detector 3 outputs a signal including the influence of characteristic X-rays emitted from the analysis sample 10 and electric noise generated from the X-ray source 2, the X-ray detector 3, and the like. The proportional amplifier 7 and the wave height discriminator 8 perform signal processing on the signal detected by the X-ray detector 3 to obtain a spectral characteristic. FIG. 3B schematically shows the spectrum characteristic C obtained at this time. The spectrum characteristic C is a spectrum in which noise is superimposed on characteristic X-rays in the low energy region and the high energy region (step S4).
[0037]
By performing an operation of subtracting the spectrum B from the spectrum C, a low energy noise component and a characteristic X-ray signal in a high energy region are removed, and only a characteristic X-ray signal in a low energy region is obtained. However, the operation of subtracting the spectrum B from the spectrum C is limited to the low energy region. That is, only the energy region absorbed by the atmosphere in the container 4 is subtracted. FIG. 3C schematically shows the spectrum characteristic A of the characteristic X-ray in the low energy region obtained by this calculation (step S5).
[0038]
FIG. 4 is a schematic diagram for explaining another configuration example of the X-ray analyzer of the present invention. In the configuration example shown in FIG. 4, as in FIG. 1, an X-ray fluorescence analyzer that irradiates an analysis sample with primary X-rays to detect characteristic X-rays (fluorescence X-rays) is taken as an example. EPMA that irradiates an electron beam onto the substrate and detects characteristic X-rays may be used.
[0039]
The configuration example shown in FIG. 4 uses a filter 11 instead of air or gas to remove the noise component. The filter 11 can be freely inserted into and removed from the optical path connecting the analysis sample 10 and the X-ray detector 3. Can be configured as shown in FIG.
[0040]
The filter 11 includes a material that absorbs at least low-energy X-rays. For example, a polymer filter, beryllium foil or aluminum foil, or a polymer filter obtained by depositing aluminum or the like can be used. The filter 11 can be freely put in and out of the optical path by the moving mechanism 12 or the like.
[0041]
An analysis procedure according to the configuration example of the X-ray analyzer shown in FIG. 4 will be described with reference to a flowchart shown in FIG.
[0042]
The analysis sample 10 is introduced and placed in the container 4 (step S11), the inside of the container 4 is evacuated by the vacuum pump 5 to a vacuum state (step S12), and the inside of the container 4 is evacuated to a primary X-ray from the X-ray source 2. The X-ray detector 3 irradiates the X-ray to the analysis sample 10 and detects characteristic X-rays emitted from the analysis sample 10.
[0043]
At this time, a filter 11 is arranged on an optical path connecting the analysis sample 10 and the X-ray detector 3, and the X-ray detector 3 detects characteristic X-rays emitted from the analysis sample 10 after passing through the filter 11. Since the filter 11 is disposed between the analysis sample 10 and the X-ray detector 3, characteristic X-rays with low energy are absorbed by the filter 11. Therefore, the X-ray detector 3 outputs only the influence of electric noise generated from the X-ray source 2, the X-ray detector 3, and the like. The proportional amplifier 7 and the wave height discriminator 8 perform signal processing on the signal detected by the X-ray detector 3 to obtain a spectral characteristic. FIG. 3A schematically shows the spectrum characteristic B obtained at this time, and includes a noise component at a low energy and a characteristic X-ray at a high energy region (step S13).
[0044]
Next, the filter 11 is removed from the optical path and detected by the X-ray detector 3. At this time, since the space between the analysis sample 10 and the X-ray detector 3 is in a vacuum state, characteristic X-rays are not absorbed. Therefore, the X-ray detector 3 outputs a signal including the influence of characteristic X-rays emitted from the analysis sample 10 and electric noise generated from the X-ray source 2, the X-ray detector 3, and the like. The proportional amplifier 7 and the wave height discriminator 8 perform signal processing on the signal detected by the X-ray detector 3 to obtain a spectral characteristic. FIG. 3B schematically shows the spectrum characteristic C obtained at this time. The spectrum characteristic C is a spectrum in which noise is superimposed on characteristic X-rays in the low energy region and the high energy region (step S14).
[0045]
By performing an operation of subtracting the spectrum B from the spectrum C, a low energy noise component and a characteristic X-ray signal in a high energy region are removed, and only a characteristic X-ray signal in a low energy region is obtained. However, the operation of subtracting the spectrum B from the spectrum C is limited to the low energy region. That is, only the energy region absorbed by the filter 11 is subtracted. FIG. 3C schematically shows the spectrum characteristic A of the characteristic X-ray in the low energy region obtained by this calculation (step S15).
[0046]
According to the embodiment of the present invention, a characteristic X-ray signal buried by electric noise can be extracted in quantitative / qualitative analysis using low-energy characteristic X-rays such as carbon (C) and boron (B). Further, according to the embodiment of the present invention, it is possible to remove the influence of electrical noise without deteriorating the value of S / N.
[0047]
【The invention's effect】
As described above, according to the present invention, the influence of electrical noise can be removed in X-ray analysis using low-energy characteristic X-rays.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining a configuration example of an X-ray analyzer according to the present invention.
FIG. 2 is a flowchart for explaining the order of analysis by the X-ray analyzer of the present invention.
FIG. 3 is a spectrum characteristic diagram obtained by the X-ray analyzer of the present invention.
FIG. 4 is a schematic diagram for explaining another configuration example of the X-ray analyzer of the present invention.
FIG. 5 is a flowchart for explaining the order of analysis by the X-ray analyzer of the present invention.
FIG. 6 is a spectrum characteristic diagram for explaining a detection signal due to superposition of electrical noise.
FIG. 7 is a diagram for explaining electric noise removal by an electric filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... X-ray analyzer, 2 ... X-ray tube, 3 ... X-ray detector, 4 ... container, 5 ... vacuum pump, 6 ... leak valve, 7 ... proportional amplifier, 8 ... wave height discriminator, 9 ... display device, 10: analysis sample, 11: filter, 12: filter driving device.

Claims (4)

In an X-ray analysis method for counting low-energy characteristic X-rays, a first measurement step of measuring characteristic X-rays in a vacuum state on an optical path between an analysis sample and an X-ray detector;
A second measurement step of measuring a residual characteristic X-ray that has absorbed low-energy X-rays on the optical path;
A calculating step of subtracting the signal counted in the second measuring step from the signal counted in the first measuring step. 2. The X-ray analysis method according to claim 1, wherein in the second measurement step, a filter that absorbs an air state or a heavy element gas state on an optical path, or at least a low energy X-ray is arranged. 3. . An X-ray analyzer that counts low-energy characteristic X-rays, a probe source that emits characteristic X-rays to a sample,
An X-ray detector for detecting characteristic X-rays,
An X-ray analysis apparatus comprising: an arithmetic unit for performing an operation of subtracting a measurement signal of only a noise component from a measurement signal including a low-energy characteristic X-ray and a noise component measured by the X-ray detector, respectively. . An X-ray analyzer that counts low-energy characteristic X-rays, a probe source that emits characteristic X-rays to a sample,
An X-ray detector for detecting characteristic X-rays,
A filter that absorbs low-energy X-rays,
An X-ray analyzer, wherein the filter is freely put in and out of an optical path of characteristic X-rays detected by an X-ray detector.

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