JP3981976B2 - X-ray analysis method - Google Patents

Description

[0001]
BACKGROUND 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, 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. X-ray analysis such as EPMA (Electron Probe Microanalyzer) that performs quantitative analysis to determine the quantity, qualitative and quantitative measurement of elements on the sample surface layer, secondary analysis of element concentration, and state analysis is known ing.
[0003]
In EPMA, the sample surface is irradiated with electrons emitted from an electron gun, and in the fluorescent X-ray analysis, the sample surface is irradiated with X-rays emitted from an X-ray source. When electrons or X-rays accelerated at a high voltage irradiate the sample surface, the inner shell electrons of the atoms of the sample substance element are excited by the energy of the incident electrons and X-rays and ejected to the outer shell. At this time, electrons in the outer shell fall, and energy corresponding to the difference in energy between the electrons in the outer shell and the inner shell is emitted as characteristic X-rays. Since this value has an element-specific value, the emitted X-ray also has a specific wavelength and energy. By measuring the wavelength or energy and intensity of the characteristic X-ray, the element of the sample surface material can be qualitatively / quantified.
[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. In order to improve the detection performance, the semiconductor detector is cooled by a dual portion containing liquid nitrogen connected through a cold finger. The characteristic X-rays detected by the semiconductor detector are amplified by a proportional amplifier for the pulse signal for each element, and then the energy of all elements is selected by a multichannel wave height selector, and the spectrum of the characteristic X-ray is simultaneously displayed on the display device. indicate.
[0005]
Semiconductor detectors are vulnerable to electrical noise from disturbances, and if this electrical noise is superimposed on an electrical signal processing circuit, the analysis of its characteristic X-rays will be hindered. As a cause of this electrical noise, there is an electric motor that drives a collimator that limits the incident amount of characteristic X-rays, and a technique for suppressing the generation of electrical noise itself by using air pressure instead of this electric motor, For example, it is shown in Patent Document 1.
[0006]
[Patent Document 1]
JP 2001-43822 A (FIG. 3)
[0007]
[Problems to be solved by the invention]
The electric noise detected by the detector includes an X-ray source, an exhaust pump, a detector itself, an amplifier, and the like in addition to the electric motor that is the driving source of the collimator. The above method cannot deal with static noise.
[0008]
FIG. 6 is a spectrum characteristic diagram for explaining a detection signal due to superposition of electrical noise. FIG. 6A shows a spectral characteristic A of a sample that does not contain electrical noise and a spectral characteristic B of electrical noise. Here, the spectral characteristic A of the sample is an ideal state in which no electrical noise is included, and the signal actually detected from the detector is, as shown in FIG. It is detected as an included spectral characteristic C. The spectral characteristic B of electrical noise has a strong signal intensity in a region where the peak value is low, as indicated by a broken line shown in FIG. Therefore, in the spectral characteristic C including electrical noise, the signal intensity in the region where the peak value is low is obtained by superimposing the electrical noise 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]
For electrical noise detected by the detector, a pulse height discriminator (PHA) is used to select a signal having a certain height or higher from the detected pulse signal, or an electrical gate such as a filter (low level limiter). In general, signals below a certain level are excluded as noise, and signals below that level are not counted as noise.
[0010]
However, noise removal by such a filter not only deteriorates the S / N ratio (signal to noise ratio), but also may cause an erroneous signal.
[0011]
FIG. 7 is a diagram for explaining electrical noise removal by an electrical filter. In FIG. 7A, an alternate long and short dash line D indicates filter characteristics, cuts a signal in a region having a low peak value, and passes a signal in a region having a high peak value. This filter characteristic suppresses electrical noise having a strong signal intensity in a region having a low peak value.
[0012]
FIG. 7B shows a spectral characteristic E (broken line in FIG. 7B) obtained by removing electrical noise with an electrical filter. When the spectral characteristic E (broken line in FIG. 7B) obtained by this electrical filter is compared 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 deviating 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 wave height discriminator is not always constant, and the total amount of characteristic X-rays generated varies depending on the sample to be analyzed. The amount of noise that occurs is also changed. In particular, in the case of the energy dispersion method using one detector, the influence becomes large.
[0014]
As described above, in quantitative / qualitative analysis using characteristic X-rays, especially low-energy characteristic X-rays, it is required to remove the influence of electrical noise and extract signals from light elements.
[0015]
Therefore, the present invention aims to solve the above-described conventional problems and to remove the influence of electrical noise in X-ray analysis using low-energy characteristic X-rays.
[0016]
[Means for Solving the Problems]
In the X-ray analysis using the low-energy characteristic X-ray, the present invention obtains a detection signal including the low-energy characteristic X-ray and the noise component and a detection signal containing only the noise component, respectively. The signal from which the influence of the electrical noise is removed is obtained by subtracting the detection signal only for the noise from the detection signal including the noise. Here, the low energy characteristic X-rays are generated from light elements such as carbon (C) and boron (B).
[0017]
The X-ray analysis of the present invention can be performed by a method and an apparatus.
[0018]
According to an embodiment of the method of the present invention, in the X-ray analysis method for counting low energy characteristic X-rays, a first measurement is performed in which a characteristic X-ray is measured in a vacuum state on an optical path between an analysis sample and an X-ray detector. A process, a second measurement process for measuring residual characteristic X-rays that have absorbed low-energy X-rays on the optical path, and subtracting the signal counted in the second measurement process from the signal counted in the first measurement process And an arithmetic step.
[0019]
In the first measurement process, since the optical path between the analysis sample and the X-ray detector is in a vacuum state, noise is superimposed on the low-energy characteristic X-rays in the signal obtained by the X-ray detector. Yes. On the other hand, in the second measurement process, 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 is only noise.
[0020]
Therefore, in the calculation process, it is low if the noise obtained by counting in the second measurement process is subtracted from the signal in which the noise 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. Low energy characteristic X-rays superimposed with noise When passed through the atmosphere, the low energy characteristic X-rays are absorbed by heavy elements contained in the atmosphere, and in the low energy region, only the noise is X-ray detector. Will be reached.
[0022]
In the second embodiment, a heavy element gas state is set on the optical path. 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 components are emitted from the X-ray detector. Is output.
[0023]
In the third embodiment, a filter that absorbs at least low-energy X-rays is disposed on the optical path. As the filter, for example, a polymer filter, a beryllium foil or an aluminum foil, a polymer filter obtained by vapor-depositing aluminum or the like can be used. When low energy characteristic X-rays and noise components are superimposed, the low energy characteristic X-rays are absorbed by heavy elements contained in the filter and do 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 form of the aspect of the apparatus according to the present invention is an X-ray analyzer that counts low-energy characteristic X-rays, a probe source that emits characteristic X-rays to a sample, and an X that detects characteristic X-rays. It is configured to include a line detector and a calculation means for performing a calculation for subtracting a measurement signal for only noise from a measurement signal including characteristic X-rays and noise respectively measured by the X-ray detector.
[0025]
Here, the probe source can be an X-ray source or an electron source. By irradiating the analysis sample with a primary X-ray emitted from the X-ray source or an electron beam emitted from the electron source, Emits characteristic X-rays of energy inherent to the element.
[0026]
In the first apparatus configuration, the first measurement process and the second measurement process described above are performed by an X-ray detector, a measurement signal including a low energy characteristic X-ray and noise, and a measurement including only noise. The signal is obtained, and the low energy characteristic X-ray is obtained by subtracting the measurement signal only for the noise from the measurement signal containing the low energy characteristic X-ray and the noise by the calculating means.
[0027]
According to a second aspect of the embodiment of the present invention, there is provided an X-ray analyzer for counting low energy characteristic X-rays, a probe source for emitting characteristic X-rays to a sample, and X-ray detection for detecting characteristic X-rays. And a filter that absorbs low-energy X-rays.
[0028]
Here, the filter is configured to be freely put into 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 can be obtained. On the other hand, when measurement is performed with a filter disposed on the optical path, low-energy characteristic X-rays are absorbed by the filter, so that a measurement signal only for noise can be obtained.
[0029]
Low-energy characteristic X-rays that do not contain noise are removed by subtracting the measurement signal measured with the filter placed 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]
DETAILED DESCRIPTION OF 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 an example of the configuration of the X-ray analyzer of the present invention. In the configuration example shown in FIG. 1, a fluorescent X-ray analyzer that detects primary X-rays and detects characteristic X-rays (fluorescent X-rays) is used as an example. However, the analytical sample is irradiated with an electron beam. EPMA for detecting characteristic X-rays can also be used.
[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 an analysis sample 10 disposed in the container 4 with primary X-rays emitted from the X-ray tube 2. Thus, characteristic X-rays are generated and detected by the X-ray detector 3. The pulse signal for each element detected by the X-ray detector 3 is amplified by a proportional amplifier 7 and then discriminated by the peak value (energy) of all elements by a wave height discriminator 8 such as a multi-channel wave height selector. And the characteristic X-ray spectrum 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 exhausting or opened to the atmospheric state by opening the leak valve 6. Moreover, the inside of the container 4 can also be made into a specific gas state by providing the gas source and valve which are not shown in figure. The gas source sufficiently attenuates the characteristic X-ray of the target element (for example, carbon (C) or boron (B)) used by the X-ray analyzer of the present invention such as nitrogen gas or carbon dioxide. A gas that can be used.
[0034]
The analysis procedure by the X-ray analyzer shown in FIG. 1 will be described according to the flowchart shown in FIG. FIG. 3 is a spectral characteristic diagram obtained with an 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 to the analysis sample 10 from the X-ray source 2 while the inside of the container 4 is in an atmospheric state, and emitted from the analysis sample 10. The characteristic X-rays thus detected 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 the atmospheric state, the low-energy characteristic X-rays are absorbed by heavy element gas molecules contained in the atmosphere. Therefore, the X-ray detector 3 outputs only the influence of electrical 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 process the signal detected by the X-ray detector 3 to obtain a spectral characteristic. FIG. 3A shows an outline of the spectral characteristic B obtained at this time, and includes noise at low energy and characteristic X-rays in a high energy region (step S2).
[0036]
Next, the inside of the container 4 is evacuated by the vacuum pump 5 (step S3), and the analysis sample 10 is irradiated with primary X-rays from the X-ray source 2 while the inside of the container 4 is in a vacuum state. The characteristic X-rays are detected by the X-ray detector 3. At this time, the characteristic X-ray is not absorbed because the analysis sample 10 and the X-ray detector 3 are in a vacuum state. Therefore, the X-ray detector 3 outputs a signal including the characteristic X-rays emitted from the analysis sample 10 and the influence of electrical noise generated from the X-ray source 2 and the X-ray detector 3. The proportional amplifier 7 and the wave height discriminator 8 process the signal detected by the X-ray detector 3 to obtain a spectral characteristic. FIG. 3B shows an outline of the spectral 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 spectrum B from spectrum C, low energy noise and characteristic X-ray signals in the high energy region are removed, and only characteristic X-ray signals in the low energy region are obtained. However, the calculation for subtracting the spectrum B from the spectrum C is performed only in the low energy region. That is, only the energy region absorbed by the atmosphere in the container 4 is subtracted. FIG. 3C shows an outline of 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, the X-ray fluorescence analyzer that detects the characteristic X-rays (fluorescence X-rays) by irradiating the analysis sample with primary X-rays is taken as an example. EPMA for detecting characteristic X-rays by irradiating an electron beam to the electron beam.
[0039]
The configuration example shown in FIG. 4 uses a filter 11 instead of the atmosphere or gas for removing noise, and allows the filter 11 to be inserted and removed freely on the optical path connecting the analysis sample 10 and the X-ray detector 3. The configuration can be the configuration shown in FIG.
[0040]
The filter 11 includes a material that absorbs at least low-energy X-rays. For example, a polymer filter, a beryllium foil or an aluminum foil, a polymer filter obtained by depositing aluminum or the like, and the like can be used. The filter 11 can be freely inserted into and removed from the optical path by the moving mechanism 12 or the like, for example.
[0041]
An analysis procedure according to the configuration example of the X-ray analyzer shown in FIG. 4 will be described with reference to the flowchart shown in FIG.
[0042]
The analytical sample 10 is introduced and arranged in the container 4 (step S11), the inside of the container 4 is evacuated by the vacuum pump 5 (step S12), and the container 4 is evacuated to the primary X from the X-ray source 2. The X-ray detector 3 detects the characteristic X-rays emitted from the analysis sample 10.
[0043]
At this time, the filter 11 is arranged on the optical path connecting the analysis sample 10 and the X-ray detector 3, and the characteristic X-rays emitted from the analysis sample 10 are detected by the X-ray detector 3 after passing through the filter 11. Since the filter 11 is disposed between the analysis sample 10 and the X-ray detector 3, low-energy characteristic X-rays are absorbed by the filter 11. Therefore, the X-ray detector 3 outputs only the influence of electrical 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 process the signal detected by the X-ray detector 3 to obtain a spectral characteristic. FIG. 3A shows an outline of the spectrum characteristic B obtained at this time, and includes noise at low energy and characteristic X-rays in 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, the characteristic X-ray is not absorbed because the analysis sample 10 and the X-ray detector 3 are in a vacuum state. Therefore, the X-ray detector 3 outputs a signal including the characteristic X-rays emitted from the analysis sample 10 and the influence of electrical noise generated from the X-ray source 2 and the X-ray detector 3. The proportional amplifier 7 and the wave height discriminator 8 process the signal detected by the X-ray detector 3 to obtain a spectral characteristic. FIG. 3B shows an outline of the spectral 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 spectrum B from spectrum C, low energy noise and characteristic X-ray signals in the high energy region are removed, and only characteristic X-ray signals in the low energy region are obtained. However, the calculation for subtracting the spectrum B from the spectrum C is performed only in the low energy region. That is, only the energy region absorbed by the filter 11 is subtracted. FIG. 3C shows an outline of 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, it is possible to extract a characteristic X-ray signal buried by electrical noise 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 degrading the S / N value.
[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 an example of the configuration 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 spectral 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 analysis apparatus of the present invention.
FIG. 5 is a flowchart for explaining the analysis order by the X-ray analysis apparatus of the present invention.
FIG. 6 is a spectral characteristic diagram for explaining a detection signal due to superposition of electrical noise.
FIG. 7 is a diagram for explaining electrical noise removal by an electrical 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, DESCRIPTION OF SYMBOLS 10 ... Analytical sample, 11 ... Filter, 12 ... Filter drive device.

Claims (2)

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 the optical path between the analysis sample and the X-ray detector;
A second measuring step for measuring residual characteristic X-rays that have absorbed low-energy X-rays on the optical path;
A calculation step of subtracting a signal in a low energy region from the signal counted in the second measurement step from the signal counted in the first measurement step, and removing the influence of electrical noise by the calculation step. X-ray analysis method characterized by this.   2. The X measurement according to claim 1, wherein in the second measurement step, the optical path is brought into an atmospheric state or a heavy element gas state, or a filter that absorbs at least low-energy X-rays is disposed. Line analysis method.

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