JP2948249B2 - X-ray diffraction goniometer setting method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for setting a goniometer of an X-ray diffractometer, and more particularly to a setting method characterized by a means for attenuating the intensity of an X-ray direct beam.

[Related Art] In an X-ray diffraction apparatus of a type that measures an X-ray diffraction pattern while rotating an X-ray detector around a sample, a so-called diffractometer needs to adjust (set) a goniometer. There are several stages in the setting, of which adjusting the zero point of the rotation angle of the turntable (2θ turntable) on which the X-ray detector is mounted,
In the stage of adjusting the zero point of the rotation angle of the sample stage (θ-rotation stage), the direct beam from the X-ray source is directly detected by the X-ray detector. The intensity of the direct beam is greatly attenuated by using an absorption plate because the intensity of the dike beam is much higher than the X-ray intensity detected by ordinary diffraction measurement.

FIG. 4 is a plan view for explaining the arrangement of devices when setting the goniometer at θ = 0. A half of the direct beam from the X-ray source 10 is cut off by the reference surface of a setting jig (half jig) 14 on the sample table 13 and the other half passes as it is. Is absorbed and enters the X-ray detector 18. Conventionally, an aluminum plate (thickness 0.5 mm) or a laminated aluminum plate and stainless steel plate (total thickness 0.5 mm) has been used as the absorption plate 16.

[Problem to be Solved by the Invention] Here, features of the X-ray direct beam will be described. The X-ray direct beam includes continuous X-rays and characteristic X-rays, and its spectrum is as shown by a curve 20 in FIG. 1 taking an X-ray tube of a copper target as an example. In this case, the acceleration voltage of the electron beam for generating X-rays (X-ray tube voltage)
Determines the shortest wavelength of the continuous X-ray. Curve 20 is a spectrum when the tube voltage is 20 kV.

By the way, in a high-voltage power supply for a high-output (for example, 12 to 18 kW) X-ray generator, a three-phase full-wave rectified DC high voltage is used as a tube voltage of an X-ray tube. There is ripple. FIG. 5 shows the temporal change of the tube voltage. The DC component E1 (broken line) of the tube voltage is precisely controlled by feedback control, but the ripple itself is not controlled. The input of the high-voltage power supply is taken from a normal three-phase AC power supply, but when this input voltage fluctuates, the DC component of the tube voltage is precisely controlled and does not change, but it is known that the ripple component fluctuates. I have. For example, the maximum instantaneous voltage becomes E2 or E3.

Since the shortest wavelength of continuous X-rays is determined by the above-mentioned maximum instantaneous voltage, the above-mentioned shortest wavelength fluctuates with time. For example, the shortest wavelength portion of the curve 20 in FIG. 1 shifts as time passes as shown by a broken line 21. In ordinary X-ray diffraction measurement, only characteristic X-rays are detected, so fluctuation of X-ray intensity near the shortest wavelength does not matter at all. However, when performing direct beam detection, near this shortest wavelength, The variation in the X-ray intensity causes the following problem.

Fig. 1 shows the spectral curve of the X-ray direct beam.
20, a mass absorption coefficient curve 22 of aluminum (Al) and a mass absorption coefficient curve 24 of iron (Fe) are superimposed. Since these mass absorption coefficients increase as the wavelength increases, attenuating the direct beam with a conventional absorption plate made of these materials reduces the total X-ray intensity and the spectrum shape as follows: To change. FIG. 3 is a graph of a spectrum when a direct beam having the spectrum curve 20 of FIG. 1 passes through an aluminum absorption plate. In this spectrum, the intensity near the characteristic X-rays (Kα, Kβ) is greatly attenuated, but not so much near the shortest wavelength. As a result, the intensity near the shortest wavelength is relatively emphasized. ing. X
X-rays having such a spectrum enter the line detector. If the instantaneous maximum voltage of the tube voltage fluctuates in such a situation as described above, the fluctuation of the X-ray intensity near the shortest wavelength (hatched area 26) greatly affects the total X-ray intensity, and as a result, , The detection intensity of the X-ray detector (which measures the total X-ray intensity) fluctuates. During the goniometer setting,
If the X-ray detection intensity changes irrespective of the rotation angle of the goniometer, there is a disadvantage that the setting accuracy is reduced.

The present invention has been made in view of such a situation, and an object of the present invention is that even if the instantaneous maximum voltage of the X-ray tube voltage fluctuates, the total detection intensity of the X-ray detector does not change much. It is to provide such a setting method.

Means for Solving the Problems According to the present invention, when setting a goniometer of an X-ray diffractometer, the intensity of an X-ray direct beam is attenuated by an X-ray absorption plate formed of the same material as a target of an X-ray tube. Features. For example, in the case of the most common copper target as an X-ray tube target,
An X-ray absorption plate made of copper will be used.

Another invention is characterized in that the intensity of the X-ray direct beam is attenuated by an X-ray absorbing plate formed of a material having an atomic number larger than the target material of the X-ray tube when setting the goniometer of the X-ray diffractometer. In this case, it is particularly preferable to use an X-ray absorbing plate formed of a material having an atomic number one larger than the target material. For example, a zinc X-ray absorbing plate is used for a copper target.

[Effect] In order to reduce the influence of the fluctuation near the shortest wavelength of the X-ray spectrum, the attenuation by the absorption plate should be small near the characteristic X-ray, and the attenuation by the absorption plate should be large at the smaller wavelength. For this purpose, an absorption plate made of the same material as the target is used. This absorption plate has an absorption edge at a wavelength slightly smaller than the characteristic X-rays (Kα, Kβ) of the direct beam. X-rays having a wavelength smaller than this absorption edge are very absorbed, but the absorption edge is smaller than the absorption edge. X-rays of larger wavelengths are not absorbed much. As a result, the intensity near the characteristic X-ray contributes to the total X-ray intensity, and the intensity near the shortest wavelength does not contribute much.

If a material having an atomic number greater than that of the target material is used as the absorption plate, the absorption edge is located at a wavelength smaller than the characteristic X-ray wavelength, as in the case of an absorption plate of the same material as the target. The strength can be greatly attenuated. However, since the absorption edge is shifted to the short wavelength side as compared with the absorption plate of the same material as the target, it is necessary to select the material with care so that the absorption edge does not approach the shortest wavelength. In this regard, it is safe to select a material having an atomic number one greater than the target material.

Embodiment Next, an embodiment of the present invention will be described with reference to the drawings.

First, a case where a copper absorption plate is used for a copper target will be described. In FIG. 1, the absorption edge 30 of the mass absorption coefficient curve 28 of copper (Cu) has characteristic X-rays (Kα, K
It can be seen that it is located at a smaller wavelength than just β). Specifically speaking, the wavelength of Kα = 1.541 °, K
For the wavelength of β = 1.392 °, the absorption edge wavelength of the K series = 1.3
80Å. When the X-ray direct beam is attenuated using this copper absorption plate, the spectrum becomes as shown in FIG. That is, at a wavelength smaller than the characteristic X-ray, the X-ray intensity is greatly attenuated, and is not significantly attenuated near the characteristic X-ray. Therefore, the fluctuation region 32 of the X-ray intensity near the shortest wavelength does not significantly affect the total X-ray intensity. Thereby, when the copper absorption plate is used for the X-ray tube of the copper target, the time variation of the X-ray intensity hardly occurs at the time of setting the goniometer,
A highly accurate setting operation can be performed.

For copper targets, a zinc absorption plate can also be used. Zinc has one greater atomic number than copper, and the absorption edge wavelength of the series is 1.283 °. Therefore, the absorption edge of zinc is slightly shifted to the shorter wavelength side than the absorption edge of copper. Even with such a zinc absorption plate,
Like the copper absorption plate, it is useful for greatly attenuating the intensity near the shortest wavelength of the X-ray direct beam.

Even when a material other than copper is used as the target material of the X-ray tube, the same effect as in the case of the copper target can be obtained by using an absorption plate made of the same material as the target material or a material having the next higher atomic number. Further, even in the case of an absorbing plate made of a material having an atomic number larger than that of the target material by two or more, if the atomic numbers are not far apart, it is possible to greatly attenuate the vicinity of the shortest wavelength compared to the vicinity of the characteristic X-ray.

A practical example of the combination of the target and the absorbing plate is as follows.

Target absorption plate Cu Cu, Zn Cr Cr, Fe Fe Fe, Co, Ni Co Co, Ni, Cu Mo Mo Ag Ag WW [Effect of the Invention] As described above, the present invention provides an absorption plate made of the same material as the target. Alternatively, by attenuating the X-ray direct beam using an absorption plate having an atomic number larger than that of the target, the X-ray intensity near the shortest wavelength can be greatly attenuated as compared with the vicinity of the characteristic X-ray. As a result, even if the instantaneous maximum voltage of the X-ray tube fluctuates during setting of the goniometer, the total intensity of the X-rays incident on the X-ray detector does not fluctuate so much, and a highly accurate setting operation can be performed.

[Brief description of the drawings]

FIG. 1 is a graph in which the mass absorption coefficient curve is superimposed on the spectrum of the X-ray direct beam, FIG. 2 is a graph of the spectrum after the X-ray direct beam has been attenuated by the method of the present invention, and FIG. FIG. 4 is a graph similar to FIG. 2 using an absorbing plate, FIG. 4 is an explanatory diagram of setting of a goniometer, and FIG. 5 is a graph showing a change over time of a tube voltage of an X-ray tube. 12 X-ray direct beam 16 X-ray absorbing plate 28 Mass absorption coefficient curve of copper 30 Absorption edge

Claims (5)

(57) [Claims] 1. A setting method characterized in that when setting a goniometer of an X-ray diffractometer, the intensity of an X-ray direct beam is attenuated by an X-ray absorbing plate made of the same material as a target of an X-ray tube. 2. The setting method according to claim 1, wherein an X-ray absorbing plate made of copper is used for the copper target. 3. The setting of the X-ray diffractometer, wherein the intensity of the X-ray direct beam is attenuated by an X-ray absorbing plate made of a material having an atomic number larger than the target material of the X-ray tube when setting the goniometer. Method. 4. The setting method according to claim 3, wherein an X-ray absorbing plate formed of a material having an atomic number one larger than a target material of the X-ray tube is used. 5. The setting method according to claim 4, wherein an X-ray absorbing plate made of zinc is used for the copper target.