JPH0245743A - Fluorescent x-ray analysis apparatus - Google Patents

Abstract

PURPOSE:To improve analysis sensitivity and accuracy by forming a calibration curve under plural kinds of aperture diameters by using standard samples and automatically determining the optimum aperture diameter by a computer. CONSTITUTION:Plural kinds of the standard samples which are the same material as the sample to be measured and have the known concn. of the element to be determined are prepd. and plural kinds of the diameter of the variable aperture 7 are set with the respective standard samples. The intensity data of the characteristic X-ray of the element to be determined is taken into the computer 9 for control via an X-ray detector 5. The computer 9 determines the diameter in accordance with a flow chart, sets the diameter of the aperture 9 by controlling the motor 8 and forms the calibration curve under plural kinds of the aperture diameters. The optimum aperture diameter is thus determined.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a fluorescent X-ray analyzer.

(Prior art) In the X-ray fluorescence analysis method, a sample is excited by X-ray irradiation, and fluorescence X4! is emitted from the sample. Elemental analysis of the sample is performed by spectroscopically detecting it using an X-ray spectrometer, but the X-ray extraction area of the X-ray spectrometer varies depending on the wavelength and cannot be changed freely. The irradiation area is also fixed.

If the sample is uniform and of sufficient size, the usage efficiency of the X-ray spectrometer can be increased to 100% by matching the X-ray irradiation area of the sample to the X-ray extraction area of the X-ray spectrometer or making it a little thicker.
%, the sensitivity and accuracy of the analysis will be the highest. However, if the sample is small and even if the entire surface of the sample is irradiated with X-rays, it will not reach the X-ray extraction area of the X-ray spectrometer. The scattered X-rays from the substance enter the X-ray spectrometer, and the S/N of the analysis is
This results in a decrease in the ratio. In addition, the X-ray intensity distribution in the beam cross section of the X-rays that irradiate the sample is not uniform (and the excitation of the sample is expected mainly from the characteristic X-rays of the X-ray source with a specific wavelength in the irradiated X-rays). , the irradiated X-rays also include continuous X-rays, and the scattered components of these continuous X-rays become noise.This type of noise component depends on the composition and structure of the sample (crystalline It depends on the element to be measured (whether it is amorphous or crystalline, such as the size of the crystal grains) and the element to be measured. be.

However, as described above, in the conventional fluorescence Xn analyzer, the X-ray irradiation area of the sample was fixed, and therefore analysis could not be performed with the highest possible S/N ratio in the apparatus.

(Problems to be Solved by the Invention) To provide a means for making the effective X-ray irradiation area of a sample variable in a fluorescent X-ray analyzer and setting the X-ray irradiation area optimally depending on the sample and the element to be measured. That's what I'm trying to do.

(Means for solving the problem) A variable diaphragm for limiting the X-ray flux is provided between the X-ray source and the sample or on the incident side of the X-ray spectrometer, and the aperture of this variable diaphragm is varied in several stages. Measure the target element using a standard sample at each stage, create a calibration curve for each stage of the aperture diameter, and extend each of these calibration curves to the negative side of the concentration of the target element to create a line of X-ray intensity O. Create a relationship curve between the distance from the point of concentration O of the cutting point and the aperture aperture, find the aperture aperture that minimizes the above distance, and set the aperture of the variable aperture to the aperture aperture found above. The sample to be measured was analyzed.

(Function) If a variable aperture is placed between the X-ray source and the sample or on the incident side of the X-ray spectrometer, that is, between the sample and the X-ray spectrometer, the effective
$11 The irradiation area is variable. Simply the effectiveness of the sample! 11
It is not possible to set the aperture diameter to obtain the highest S/N ratio simply by varying the irradiation area. In the present invention, first, a standard sample is used to create a calibration curve with several MM aperture diameters. Figure 3 shows the inspection ffi gland, and the aperture diameter becomes smaller in the order of A, B, and C.The inspection m line is the original 1g concentration O
The X-ray intensity at the point that cuts the vertical axis in is the background intensity. The background intensity will be lower if the aperture diameter is smaller, but the change in the X-ray intensity per unit concentration of the element will also be smaller.As an expression of the S/N ratio, the characteristic X-ray intensity of the element is the background intensity. You can use the element concentration (I3EC) that makes them equal.For the M gland, take the point ab=oa on the vertical axis, extend the horizontal line to the right from there, and draw the calibration curve A. This corresponds to the element concentration at the point of intersection.This is also equal to the length of Oc when the calibration curve is extended to the left from the vertical axis and the point C that cuts the horizontal axis is found.

It goes without saying that the smaller the BEC, the better the S/N ratio. Imaken fi [A, B.

When l3EC is determined for each of C and a graph of the relationship with the aperture diameter is created, the result is as shown in FIG. 4, and it can be seen that when the aperture diameter is D, the S/N ratio is the highest. The above operations can be performed automatically by a computer by preparing a standard sample, measuring the characteristic X-ray intensity of the target element at several aperture diameters, and importing the data, to determine the optimal aperture diameter. can.

(Embodiment) FIG. 1 shows an apparatus according to an embodiment of the present invention. In the figure, 1 is an X-ray source for sample excitation, S is a sample, and M is an X-ray spectrometer. This X
The line spectrometer is a type that uses a flat crystal as a spectroscopic element, 3 is a solar slit on the entrance side, 4 is a solar slit on the output side,
5 is an X-ray detector. Reference numeral 6 denotes a goniometer, and the output side solar slit 4 rotates by an angle twice the rotation angle of the spectroscopic crystal 2, thereby making it possible to set the X-ray wavelength to be detected. The X-ray extraction area of the X-ray spectrometer is the apparent area of the spectroscopic crystal 2 viewed from the solar slit 3 side, and is a structural value that varies depending on the X-ray wavelength but is determined by the size of the spectroscopic crystal. A variable aperture 7 has the same structure as a variable aperture of a photographic lens, and is driven by an aperture control pulse motor 8 via a gear. 9 is a control computer that takes in the output data of the X-ray detector 5;
The motor 8 is controlled by m to set the diameter of the diaphragm 7 to a predetermined value.

The aperture diameter setting operation of the variable aperture 7 will be explained below.

First, a sample with a known concentration of the element to be quantified is r%1! of the same substance as the sample to be measured. Prepare multiple types of samples, and for each standard sample, adjust the diameter of the variable aperture 7 to three types (A>B>C) (3 types).
The data on the intensity of characteristic X-rays of the element to be quantified is input into the $ control computer 9. Thereafter, the computer 9 is caused to start the aperture aperture setting operation. The computer 9 determines the aperture diameter according to the flow chart shown in FIG. 2, and controls the motor 8 to set the aperture diameter of the aperture 7. First, the aperture aperture A is determined based on the captured data.

Create the formula for the calibration curve in Figure 3 for each case of B and C (a)
do. In this case, the calibration curve is a straight line, and if there are two types of samples -
It is sufficient to create an equation for a straight line connecting the X-ray intensities for each standard sample at two aperture apertures. When there are three or more types of standard samples, determine the straight line using the least squares method. Next, calculate the element concentration BEC at which the X-ray intensity becomes O in the above equation (see below).

A, B.

C. From each calibrated aperture and the corresponding value of l3EC, the equation shown in the graph shown in FIG. 4 is determined as a quadratic equation (c). From the quadratic equation determined in (c), the aperture diameter that minimizes BEC is calculated (d). Finally, the motor 8 is controlled so that the aperture diameter calculated in (d) is achieved, and the variable aperture 7 is set (e) to end the operation.

In some cases, the relationship between the aperture diameter and BEC does not clearly indicate the aperture diameter that provides the minimum BEC, as shown in FIG. This happens when the sample is quite small compared to the maximum aperture of the aperture 7, and even if the aperture diameter is changed within a range larger than the sample, the calibration curve will simply shift vertically in parallel as shown in Figure 5.
Accordingly, the BEC also changes linearly with respect to changes in the aperture diameter. When the aperture diameter becomes smaller than the sample, the effective irradiation surface area of the sample becomes smaller (therefore, the rate of change in X-ray intensity per unit concentration of the target element, that is, the slope of the detection f11 gland begins to decrease, and the BEC stops changing. Therefore, in this case, in the quadrant showing the relationship between the aperture diameter and BEC in Fig. 5, the point α
D corresponding to the intersection of the straight line connecting β and the vertical line passing through γ
The best S/N ratio can be obtained by setting the aperture diameter to . The computer 9 is also set with a program for determining the aperture using this method when the aperture cannot be determined using the program shown in FIG.

In the embodiment described above, the variable diaphragm is placed between the X-ray source and the sample, but it may also be placed on the incident side of the incident side solar slit 3, that is, between the sample S and the solar slit 3. Furthermore, although a flat crystal type X-ray spectrometer is used as the X-ray spectrometer in the above embodiment, it goes without saying that the present invention is also applicable to a case where a curved crystal type spectrometer is used.

(Effects of the Invention) According to the present invention, it is possible to always use an X-ray spectrometer under the conditions that provide the best S/N ratio, resulting in improved analytical sensitivity and accuracy.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an apparatus according to an embodiment of the present invention, Fig. 2 is a flowchart of variable aperture setting operation, Fig. 3 is a graph showing changes in the calibration curve depending on aperture diameter, and Fig. 4 is a graph showing changes in aperture diameter and BE.
FIG. 5 is a graph illustrating another case of the relationship between the aperture diameter and BEC. 1... X-ray source, S... sample, M... X-ray spectrometer,
2... Spectroscopic crystal, 3... Solar slit on the incident side, 4
...Emission side solar slit, 5...X-ray detector, 6
... Goniometer, 7... Variable aperture, 8... Pulse motor for aperture control, 9... Control computer.

Claims (1)

[Claims] A variable diaphragm that limits the X-ray flux is provided between the X-ray source and the sample or on the incident side of the X-ray spectrometer, and the aperture of this variable diaphragm is changed in several stages. Measurement is carried out, data on the characteristic X-ray intensity of the target element in each standard sample is acquired for each stage of the aperture diameter, and a calibration curve is created for each stage of the aperture diameter. Create a relationship curve between the aperture diameter and the value corresponding to the distance from the zero concentration point to the point that extends to the negative density side and cuts the line with zero X-ray intensity, and find the aperture diameter that minimizes the above value. . A fluorescent X-ray analysis apparatus, comprising: a control means for setting the aperture aperture of the variable aperture to the aperture aperture determined above.