JPH0718823B2 - X-ray analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an X-ray analyzer, and more particularly to a vacuum degree correcting means.

(Prior Art) In X-ray fluorescence analysis of light elements, there is absorption of X-rays by air, and the measured value differs depending on the degree of vacuum. In order to eliminate the influence, a constant degree of vacuum is maintained during measurement. Since the method of maintaining the degree of vacuum of this analyzer is a mechanical method and is controlled by ON / OFF control, there remains a problem in the stability of the degree of vacuum, which has recently become possible due to the development of LSA. In the analysis of ultra-light elements such as C, absorption of X-rays due to residual air in vacuum has become a big problem. Therefore, it is necessary to stabilize the degree of vacuum, but as described above, it is difficult to measure with high accuracy by the conventional vacuum degree control.

There is also a method to correct the difference in measured values due to the difference in vacuum degree by correction based on the vacuum degree, but the sensitivity characteristics vary from vacuum gauge to vacuum gauge, and the vacuum gauge has a limited lifespan. However, it is difficult to get a fully calibrated vacuum gauge, and the labor required to calibrate the vacuum gauge makes it easy to measure absolute vacuum with high accuracy. However, as a practical problem, in the soft X-ray measurement that requires highly accurate vacuum degree stability, the accuracy of measured values cannot be expected so much at present.

(Problems to be Solved by the Invention) In the present invention, in X-ray analysis in a wavelength region where the influence of the degree of vacuum is large, it is possible to obtain high-precision X
The purpose is to enable line analysis.

(Means for Solving the Problem) In the X-ray analyzer, a program for determining the relationship between the absolute vacuum degree and the vacuum gauge output from the X-ray detection output and the output of the vacuum gauge for the standard sample of one element is provided. This relational expression is stored, the relationship between the X-ray intensity of each element of the reference concentration and the absolute vacuum degree is stored in advance, and the absolute vacuum degree and the vacuum gauge output are calculated from the output of the vacuum gauge when measuring the sample to be measured. Because of the relationship with
Data having a program for calculating the absolute vacuum degree and determining the concentration of the target element from the X-ray intensity of the sample to be measured by using the relationship between the X-ray intensity of the target element and the absolute vacuum degree stored in advance. A relation between the X-ray detection output and the output of the vacuum gauge is actually measured and stored for a standard sample having a processing element or a reference concentration of each element, and the X-ray detection output and the vacuum gauge A data processing means having a program for determining the concentration of the target element from the above relations with respect to the target element based on the output is provided.

(Operation) The degree of absorption of X-rays by air is the density of air, that is, the degree of vacuum and X
It is determined by the wavelength of the line and the optical path length, and the optical path length is determined by the structure of the spectroscope. Therefore, if the X-ray absorption of a known sample is known, the vacuum degree can be calculated backward, and the relationship is already established. Since it has been formulated, the vacuum gauge can be easily calibrated from the above formula by measuring the X-ray absorption of a standard sample corresponding to the detected value of the vacuum gauge.

Therefore, the above calibration formula is stored in the CPU, the detected value of the vacuum gauge is calibrated to obtain the absolute degree of vacuum, and the degree of vacuum is corrected for the X-ray measurement value of the sample based on this absolute degree of vacuum. Can be performed to determine the correct concentration of the target element in the sample.

The user can easily calibrate the vacuum gauge at any time if he has a fixed standard sample. Further, if the relationship between the display vacuum degree of the vacuum gauge and the X-ray detection intensity of each element standard sample is measured and stored, the same X-ray intensity of a certain element of the sample to be measured corresponds to the same vacuum gauge display value. The concentration of the element in the sample to be measured can be determined by the ratio of the element to the X-ray intensity of the standard sample. Since the number of elements in which the degree of vacuum is a problem is limited, it is easy to prepare standard samples of these elements in advance, and it is easy for the user to implement them.

The first invention of the present application will be described in more detail. Let's use the standard sample of one element and the concentration of that element as C ₀ . Using this standard sample, the reading of the vacuum gauge and Q and the X-ray detection intensity W are measured while changing the degree of vacuum of the X-ray analyzer. Assuming that the absolute vacuum degree is P, the X-ray optical path length in the apparatus is t, and the mass absorption coefficient of air with respect to the characteristic X-rays of air is μ, then W = W ₀ e ^−ρμt, where ρ = P × 1.146 × 10 ^-10 ∴LogW = LogW ₀ −ρμt From this, the absolute vacuum degree P is P = (LogW ₀ −LogW) /1.146×10 ⁻¹⁰ μt In the above formula, W ₀ and μt are values determined by the device and sample,
In this case, since the sample is a standard sample, LogW ₀ and 1.1
46 × 10 ^-10 μt can be measured and determined in advance by the manufacturer. Therefore, if LogW ₀ = A 1.146 × 10 ⁻¹⁰ μt = B, then P = A / B−LogW / B (1) to obtain the absolute vacuum degree P. On the other hand, since the vacuum gauge reading Q corresponding to the P is being measured, the empirical formula P = f (Q) can be determined. If the equipment manufacturer gives the equipment control CPU an arithmetic program for obtaining P from W according to the above constants A, B and the equation (1), the user will always use the same kind of standard sample and perform the same operation as above (1). ), An arithmetic expression of f (Q) can be created from the value of the actually measured W and the value of Q, and the absolute vacuum degree P can be determined from the displayed value of the vacuum gauge by this f (Q). As a result, when the absolute vacuum degree is obtained from the output of the vacuum gauge during the measurement of the sample to be measured, the quantitative measurement of the sample to be measured is made based on the relationship between the X-ray intensity of each element having a predetermined reference wavelength and the absolute vacuum degree. The concentration of the target element can be calculated from the X-ray intensity of the target element.

(Embodiment) FIG. 1 shows an embodiment of the present invention. In FIG. 1, B
Is an excited X-ray, S is a sample, 1 is an excited X-ray B, and a sample S
A spectroscope for separating the fluorescent X-rays emitted from the detector, 2 a detector for detecting the fluorescent X-rays dispersed by the spectroscope 1, 3 a scaler for counting the X-ray detection pulses output from the detector 2,
4 is a Pirani vacuum gauge for measuring the degree of vacuum in the spectroscope, 5 is an A / D converter for converting the detection value measured by the vacuum gauge into a digital signal, and 6 is an X-ray detection signal output from the scaler 3. In the CPU that performs the correction calculation, the absolute vacuum degree is obtained from the correlation equation obtained in advance from the vacuum degree detection signal output from the A / D converter 5, and the correction equation preset based on the absolute vacuum degree is used. Correction calculation is performed on the X-ray detection signal. Various constants required for the above calculation, such as A and B, are stored in the CPU 6 in advance. A display device 7 displays the corrected X-ray dose output from the CPU 6.

A method of calibrating the vacuum gauge 4 will be described. While gradually lowering the degree of vacuum or allowing air to leak into the apparatus to the final ultimate degree of vacuum, the output of the Pirani vacuum gauge 4 and the element of the detector 2 corresponding to the same output and one of its known concentrations The X-ray detection output for the standard sample is stored in the CPU6. After measurement, X
Based on the detection output of the line detector, the absolute vacuum degree is calculated using the equation (1), and the correlation equation between the obtained absolute vacuum degree and the output of the vacuum gauge is obtained. Explaining how to obtain it, it corresponds to the absolute vacuum degree P obtained by the above formula (1) from the X-ray detection output measured while depressurizing the vacuum degree using one standard sample, and the absolute vacuum degree. FIG. 2 shows a correlation curve drawn with the output value of the vacuum gauge 4. Based on this correlation curve, it is assumed that the correlation equation between the absolute vacuum degree P and the output value of the vacuum gauge corresponding to the absolute vacuum degree is, for example, a cubic equation, and each coefficient of the cubic equation is obtained by the least square method or the like. Remember.

When actually measuring an arbitrary sample, the absolute vacuum degree is obtained from the reading of the vacuum gauge by the above vacuum degree calibration formula, and the relational expression between the X-ray intensity Wi and the absolute vacuum degree at the reference concentration of the quantitative target element, Wi = Wi ₀ e ^−ρμ′t (2) where ρ is P × 1.146 × 10 ⁻¹⁰ and μ ′ is the mass absorption coefficient of the target element and the above absolute vacuum degree is substituted for Wi to obtain Wi, and Wi is measured. The concentration of the target element in the sample to be measured is determined by the ratio with the X-ray intensity. Μ't and Wi _{0 in the} equation (2) are constants determined by the device and the elements, and the light elements requiring vacuum degree correction are stored in the CPU 6 in advance.

In actual measurement, since the vacuum degree changes with time, the average transmittance Hm during the X-ray detection signal integration time T
The vacuum degree P is measured N times at regular intervals during the analysis time, the transmittance H (P) is calculated, and the N times are averaged to obtain Hm = [ΣH (P)] / N Then, using this average transmittance Hm, W _o = W × [1 / Hm]

(Other Example) In this example, the apparatus configuration is the same as that in FIG. 1, but the trouble of calculating the absolute vacuum degree from the reading of the vacuum gauge is not taken into consideration, and the apparatus vacuum degree is changed from time to time for the standard sample of each element. The relationship between the X-ray intensity and the reading of the vacuum gauge was measured while changing the, and the relationship between the measured X-ray intensity W at the reference concentration C of each element and the output Q of the vacuum gauge at that time Empirical formula W = g (Q) Decide CP
It is stored in U6, and the concentration C ′ of the target element is calculated from the measured X-ray intensity value W ′ of an arbitrary sample and the output Q of the vacuum gauge at that time, C ′ = C × W ′ / g (Q) It is what you ask for. In the actual measurement, the apparatus for the temporal change of the degree of vacuum during the X-ray detection signal integration time is the same as in the previous embodiment. In this embodiment, it is necessary to prepare a standard sample for each element requiring vacuum correction, but the data processing is simpler than in the previous embodiment.

(Effects of the Invention) According to the present invention, the absolute vacuum degree can be measured with high accuracy, so that the correction of the measured value by the vacuum degree becomes more accurate, and the measurement accuracy can be improved. In addition, the ability to measure with high precision has been improved without having to wait until a high vacuum has been achieved, which has improved the measurement capability.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a correlation curve diagram between an output value of a vacuum gauge and an absolute vacuum degree, and FIG. 3 is an X-ray detection intensity curve chart with respect to an actually measured vacuum degree. B ... Excited X-ray, S ... Sample, 1 ... Spectrometer, 2 ... Detector, 3
... scaler, 4 ... vacuum gauge, 5 ... A / D converter, 6 ... CPU, 7
... display device.

Claims (2)

[Claims] 1. A program for determining a relationship between an absolute vacuum degree and a vacuum gauge output from an X-ray detection output and a vacuum gauge output for a standard sample of one element, and storing this relational expression, The relationship between the X-ray intensity of each element at the reference concentration and the absolute vacuum degree is stored in advance, and the absolute vacuum degree is calculated from the output of the vacuum gauge when measuring the sample to be measured, based on the relationship between the absolute vacuum degree and the vacuum gauge output. Then, a data processing means having a program for determining the concentration of the target element from the X-ray intensity of the sample to be measured by using the relationship between the X-ray intensity of the target element and the absolute vacuum degree stored in advance is provided. An X-ray analyzer characterized by the above. 2. A standard sample having a standard concentration of each element, X
The relationship between the X-ray detection output and the output of the vacuum gauge is actually measured and stored, and when measuring the sample to be measured, the concentration of the target element is determined from the above-mentioned relationship of the target element by the X-ray detection output and the output of the vacuum gauge. An X-ray analysis apparatus comprising a data processing unit having a program.