JP3675079B2 - X-ray diffractometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray diffractometer that irradiates a sample with characteristic X-rays, detects X-rays diffracted by the sample, and performs qualitative and quantitative analysis of sample components.
[0002]
[Prior art]
An X-ray diffractometer is a device that performs qualitative and quantitative analysis of crystal components contained in powder samples and the like, irradiates the sample with characteristic X-rays from an X-ray source, and uses the diffracted X-rays emitted from the sample as a goniometer Detection is carried out for each diffraction angle by an on-board detector. As shown in FIG. 4 showing a conventional X-ray diffraction apparatus, the powder sample 23 is usually formed into a flat plate having a size of about 20 mm square using a sample holder and placed at the center of the goniometer on the θ axis 27. The spread of the X-rays 26 generated at the target of the X-ray tube 21 is restricted to about 1 to 3 ° by the diverging slit 22 having a predetermined installation position and slit width, and is irradiated on the surface of the sample 23. The 2θ axis of the goniometer is rotationally driven while maintaining a double relationship with the θ axis, and the diffracted X-ray radiated from the sample 23 is detected by the detection slit 24 and the detector 25 mounted on the 2θ axis 28. Is done.
[0003]
The measured X-ray intensity is the same as the condition of the sample, such as the usage time of the X-ray tube as an X-ray source, the state of a detector such as a scintillation counter that detects diffracted X-rays from the sample, and Depends on the ambient environment such as room temperature. For example, tungsten evaporated from the filament gradually accumulates on the window provided on the side wall of the X-ray tube that transmits X-rays generated by the X-ray tube target, and the intensity of the transmitted X-ray is determined by the usage time. It goes down with it. The scintillation counter used as a detector uses a scintillator made of NaI or the like that converts X-rays into visible light. However, since this scintillator is sensitive to moisture, the efficiency of converting X-rays into light may be increased depending on the usage environment. This will also reduce the measured X-ray intensity.
[0004]
In the conventional X-ray diffractometer apparatus, no special measures are taken for such a relatively long-term intensity change, and no correction is made to the measured X-ray intensity.
[0005]
[Problems to be solved by the invention]
As described above, in the prior art, effective correction was not performed for changes in measured X-ray intensity due to deterioration with time of each part of the X-ray diffractometer or changes in the surrounding environment. However, there is a problem that the quantitative accuracy decreases with time, or if it is attempted to maintain the quantitative accuracy, it takes time to rewrite the calibration curve for each measurement of the sample to be analyzed.
[0006]
The present invention has been made in view of such circumstances, and in an X-ray diffractometer, corrects a change in measurement intensity corresponding to deterioration of a tube, a detector, or the like or an environmental change such as an ambient temperature. Therefore, it is an object to improve the quantitative accuracy by always obtaining the X-ray intensity at the beginning of device adjustment.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention uses a reference in an X-ray diffraction apparatus including an X-ray source that irradiates a sample with characteristic X-rays and a detector that detects X-rays diffracted by the sample. A storage means for storing a reference intensity when the reference sample is measured at a time point; an analysis time intensity of the reference sample measured at the time of measuring the analysis target sample; and the analysis target sample based on the stored reference intensity Computation means for obtaining a correction formula for correcting the measurement intensity is provided, and changes in the X-ray intensity of the analysis target sample due to changes in the state of the X-ray source, detector, etc. are corrected during measurement of the analysis target sample. And
[0008]
The measurement intensity at the reference time point of the reference sample that does not change over time is stored, and after a certain date has passed, the measurement intensity when measuring the sample to be analyzed is the intensity at the time of analysis of the reference sample that was remeasured at that time. Therefore, it is possible to cancel the change with time of the X-ray source and the detector and to obtain an accurate quantitative analysis result.
[0009]
Here, the reference time point is the time when the apparatus is installed or immediately after regular maintenance is performed and the X-ray diffractometer exhibits good performance.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic diagram of an X-ray diffraction apparatus of the present invention. X-rays radiated from the X-ray tube 1 are applied to the sample 2, and X-rays diffracted by the sample 2 are detected by the detector 3. The sample 2 and the detector 3 are mounted on the θ axis and 2θ axis of the goniometer 4, respectively, and are rotated around the central axis of the goniometer by a so-called θ-2θ interlocking driving method, and the X-ray intensity for each diffraction angle. Are measured, and an X-ray diffraction pattern is obtained.
[0011]
The signal from the detector 3 is converted into digital data by the intensity measurement circuit 5a included in the control unit 5, sent to the data processing unit 6, and stored in the measurement data memory 6a. The operation control circuit 5b in the control unit 5 controls the power of the X-ray tube 1 and the rotational drive of the goniometer 4. The controller 5 includes an analog circuit for X-ray counting, a microcomputer for digitally controlling operation, an input / output device, and the like. The data processing unit 6 can be configured by a personal computer or the like, and performs various data processing as an X-ray diffraction apparatus based on X-ray diffraction data obtained as a result of measurement, and is configured by a CRT, a printer, or the like. The analysis result is output to the output / display unit 7.
[0012]
As a characteristic configuration of the present invention, a reference intensity memory 6b for storing X-ray intensity data when a reference sample is measured in the data processing unit 6, a correction function memory 6c for storing a correction function (correction coefficient), A calculation unit 6d is provided that calculates a correction function and corrects the measurement intensity of the sample to be analyzed.
[0013]
Next, a method for correcting and calculating the measurement intensity of the sample to be analyzed will be described using the flowchart of FIG. When the X-ray diffractometer is installed for the first time or when regular maintenance is performed, it is regarded as a reference time point, and at that time, as shown in FIG. Remember state. That is, a sample whose properties such as crystal structure and surface state do not change over time is selected as a reference sample, and the X-ray diffraction intensity by the reference sample is measured under the measurement conditions for actual analysis ( S1). The measurement conditions are various conditions that can be set as a device such as power applied to the X-ray tube and integration time of intensity measurement. Of course, there may be several types of measurement conditions required, and the intensity of the reference sample may be measured under each measurement condition. The reference sample is not limited to one type and one. The X-ray intensity of the reference sample thus measured is stored in the reference intensity memory 6b (S2).
[0014]
When actually analyzing the sample to be analyzed, it is necessary to calibrate the sensitivity of the entire device because some degree of X-ray tube deterioration is inevitable if time has passed since the previous maintenance of the device. is there. For this purpose, the measurement intensity is corrected based on the intensity of the reference sample previously measured as shown in FIG. First, the X-ray intensity is measured under the same measurement conditions as when the reference intensity is measured using the reference sample (S11), and the correction function is based on the intensity Km obtained at this time and the reference intensity Ks obtained during maintenance. F (Km) is obtained (S12). An example of the correction function will be described later. Next, the diffraction pattern of the sample to be analyzed is measured (S13), the obtained measurement intensity Im is applied to the correction function F, and the corrected intensity Ih is obtained as Ih = F (Im) (S14). Thereafter, this Ih is treated as the measured intensity, and normal qualitative analysis and quantitative analysis are performed (S15). When another measurement is subsequently performed, the step of obtaining the correction function is not performed, and the process returns to S13 and the subsequent measurement is repeated (S16).
[0015]
An example of the correction function and how to obtain it will be described with reference to FIG. In the graph shown in FIG. 3, the horizontal axis of the graph written as the reference time point and the measurement time point is the diffraction angle (2θ angle), and the vertical axis is the measured X-ray intensity. Further, the horizontal axis of the graph written as the correction function is the X-ray intensity of the reference sample at the time of measurement, and the vertical axis is the X-ray intensity of the reference sample at the reference time.
[0016]
FIG. 3A shows an example of correction using one reference intensity value, and the correction function is a straight line passing through the origin. Measure the intensity of the appropriate diffraction peak of the reference sample (the peak angle is θ1), obtain the reference intensity Ks at the reference time immediately after maintenance, etc., and obtain the intensity Km at the measurement time to measure the sample to be analyzed. Assuming that, the relationship between the intensity Im before correction of the sample to be analyzed and the intensity Ih after correction, that is, the correction formula is as follows.
[0017]
Ih = αIm (1)
Where α = Ks / Km (2)
It is.
[0018]
FIG. 3B shows a correction method using two reference intensity values, and the correction function is a straight line passing through two points. Two reference samples having different X-ray intensities measured by changing the concentrations of components contained in the sample are prepared, and the intensity of each reference sample of an appropriate diffraction peak is measured. If the reference intensities at the reference time are Ks1 and Ks2, respectively, and the intensities at the time of measurement for measuring the sample to be analyzed are Km1 and Km2, the relationship between the intensity Im before correction and the intensity Ih after correction, ie, The correction formula is as follows.
[0019]
Ih = αIm + β (3)
Where α = (Ks1−Ks2) / (Km1−Km2) (4)
β = (Ks2Km1-Ks1Km2) / (Km1-Km2) (5)
It is.
[0020]
FIG. 3 (c) shows a more general correction method using three or more reference intensity values, and the correction function is a second or higher order polynomial. Three or more reference intensity values may be measured by preparing three or more reference samples having different X-ray intensities as in the method described in FIG. 3 (b). As described above, the value of the apex of one peak profile and its skirt may be used. For example, assuming that four intensities are used, the X-ray intensities of the reference samples at the diffraction angles θ1, θ2, θ3, and θ4 at the reference time are Ks1, Ks2, Ks3, and Ks4, and the respective intensities at the measurement time are Km1. , Km2, Km3, and Km4, the relationship between the intensity Im before correction of the sample to be analyzed and the intensity Ih after correction, that is, the correction equation is as follows.
[0021]
Ih = F (Im) (6)
Here, the correction function F (Im) is a four-point data set represented by a quadratic polynomial by the least square method or the like. The order of the correction function is not limited to the second order, and may be a third or higher order polynomial depending on the number of data points.
[0022]
【The invention's effect】
Since the X-ray diffractometer of the present invention corrects the measured X-ray intensity data using the data of the reference sample that does not change with time, the apparatus can always be considered to be in the best state. X-ray intensity data that is not affected by the deterioration of each component or the surrounding environment can be obtained. Since the corrected data is used in qualitative analysis or quantitative analysis as an X-ray diffractometer, the obtained result is highly reliable.
[0023]
In quantitative analysis, a calibration curve created using a standard sample is used. Since the X-ray intensity data obtained by the X-ray diffraction apparatus of the present invention is highly reliable, There is no need to rewrite the calibration curve when measuring the sample, and it is possible to perform a quick analysis without taking time and effort.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an X-ray diffraction apparatus according to the present invention.
FIG. 2 is a flowchart showing a procedure for measuring X-ray intensity using the X-ray diffraction apparatus of the present invention.
FIG. 3 is an example of a correction function used in the X-ray diffraction apparatus of the present invention.
FIG. 4 is a view showing a conventional X-ray diffraction apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... X-ray tube 2 ... Sample 3 ... Detector 4 ... Goniometer 5 ... Control part 6 ... Data processing part 7 ... Output / display part 21 ... X-ray tube 22 ... Divergence slit 23 ... Sample 24 ... Detection slit 25 ... Detector 26 ... X-ray 27 ... θ axis 28 ... 2θ axis

Claims (1)

In an X-ray diffractometer equipped with an X-ray source that irradiates a sample with characteristic X-rays and a detector that detects X-rays diffracted by the sample, two or more when a reference sample is measured at a reference time point The storage means for storing the reference intensity, and two or more analysis time points when the reference sample is measured under the same measurement conditions as when the reference intensity is measured at the time of measuring the sample to be analyzed, and the storage means Computation means for obtaining a correction formula for correcting the measurement intensity of the sample to be analyzed based on the stored reference intensity, the time-dependent deterioration of each part of the X- ray diffractometer and the fluctuation of the surrounding environment during measurement of the sample to be analyzed An X-ray diffractometer characterized by correcting changes in X-ray intensity of a sample to be analyzed due to the above.

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