JPS6243160B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved channel cut monochromator, and more particularly to an improved X-ray monochromator in which the position of the spectral X-ray does not change due to rotation of the monochromator.

An X-ray monochromator is used for the purpose of extracting monochromatic X-rays of any desired wavelength component from incident X-rays. A single crystal flat plate is normally used as an X-ray monochromator, and as shown in Figure 1, if the lattice spacing of the crystal used is d, and the angle formed by the incident X-ray with respect to the lattice plane is θ, then the single crystal plate The wavelength λ of the X-rays to be separated is given by λ=2dsinθ (Bragg's equation) (1).

Therefore, in order to obtain X-rays of the desired wavelength, the incident angle θ may be adjusted by angular rotation of the crystal plate. However, the spectroscopic X-rays are emitted in a direction at an angle of 2θ with respect to the direction of the incident It was inconvenient to use the line.

For example, as shown in Figure 2, EXAFS
(Extended X-ray Absorption Fine
When used to measure X-ray absorption fine structure (X-ray absorption fine structure), X-rays incident from the X-ray source 4 through the slit 5 onto the crystal plate 1 on the θ rotating plate 2 at an incident angle θ are dispersed at an angle of 2θ. A sample 7 of an appropriate thickness on a 2θ rotary plate 3 is irradiated with the X-ray beam, and the transmitted X-ray intensity is detected by an X-ray detector 6, and the incident X-ray intensity (measured after removing the sample) is measured. Then, by calculating the X-ray absorption coefficient from the intensities of both, and continuously changing the wavelength to shorter than the absorption edge, a fine structure appears in the absorption curve, which is called EXAFS.

This is due to the influence of neighboring atoms surrounding the atom that absorbs X-rays, and information regarding the spatial arrangement of neighboring atoms can be obtained. In this case, as the crystal plate is rotated by θ, a mechanism for rotating the crystal plate by 2θ is required, resulting in a complicated apparatus. Furthermore, there was the difficulty of having to place various additional devices on the rotating plate depending on the analysis conditions, such as when keeping the sample at a low temperature or under high pressure.

In order to solve these problems, a channel cut monochromator as shown in FIG. 3 has been proposed. This is done by repeatedly reflecting between parallel crystal plates cut out from one single crystal block so that the direction of the incident X-ray and the direction of the selected X-ray do not change. At this time, Figure 3,
As shown in FIG. 4, the first crystal 8a is made from the same crystal block because strict parallelism is required.
and the width of the channel (groove) of the second crystal 8b is D,
If the distance between the OPs is r and the angle of incidence is θ, then the incident
When the ray is incident on the lattice plane of the first crystal 8a at an angle of θ, only the wavelength component λ according to equation (1) above is reflected in a direction 2θ with respect to the direction of the incident X-ray and is incident on the second crystal 8b. However, since the lattice planes of the first and second crystals are parallel, θ
Since the X-rays are incident at an angle of 2θ and reflected in the 2θ direction, the twice-reflected X-rays are emitted parallel to the incident X-rays.

Here, if the distance between the incident X-ray and the spectral X-ray is H, then in Figure 4, H = r sin2θ = D/sinθsin2θ = 2D cosθ (2), and when the monochromator is rotated by θ to change the wavelength of the X-ray, H changes. In other words, the spectroscopic X
Since the line moves in parallel, the position of the sample must be changed when used for the above-mentioned X-ray absorption analysis, and a position correction mechanism for the sample stage is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray monochromator in which the position of spectral X-rays does not move even when the monochromator is rotated.

In order to achieve the above object, an X-ray monochromator according to the present invention is a monochromator comprising first and second crystals having crystal lattice planes parallel to each other, in which a point on the first crystal lattice plane is set as the origin, and a point on the first crystal lattice plane is set as the origin. When the x-axis is parallel to the lattice plane and the y-axis is perpendicular to the lattice plane, the opposing second crystal surface is 1/X ² +
It is given by the formula 1/y ² =4/H ² (where H is the distance between the incident X-ray and the spectral X-ray).

The present invention will be explained in more detail below using the drawings and the like.

FIG. 4 is a perspective view showing an embodiment of the X-ray monochromator of the present invention, and FIG. 5 is a plan view thereof. The two crystals will be called a first crystal 9a and a second crystal 9b according to the order of incidence. Since the lattice planes of the first and second crystals are required to be strictly parallel, they are made of the same block as shown in FIG.

As shown in FIG. 5, the origin O is placed on the surface of the first crystal 9a, the x-axis is parallel to the lattice plane, and the y-axis is perpendicular to the lattice plane.

Now, when the entire crystal is rotated by θ around the axis perpendicular to the plane of the paper with point O as the center, the distance H between the incident X-ray and the spectral X-ray becomes a constant value regardless of θ. Search for shape.

Assuming that the distance r and H between point O and point P (x, y) are constant, r=H/sin2θ (3) The coordinates x and y of point P are: x=r cosθ = H/2sinθ・cosθ・cosθ= H/2sin
θ (4a) y=r sinθ =H/2sinθ・cosθ・sinθ=H/2cos
It is given by θ(4b). The equation of the curve obtained from equations (4a) and (4b) is sin ² θ + cos ² θ = 1, so 1/x ² + 1/y ² = (2/H) ² (sin ² θ + cos ² θ
)=4/H ² (5), and by making the surface shape of the second crystal 9b conform to equation (5), the value of H does not change even if the θ rotation is performed.

As explained in detail above, according to the present invention, the second
By making the shape of the crystal surface into an appropriate curve, the wavelength of the incident X-rays can be changed. Even if the incident angle θ is changed, the position of the spectroscopic X-rays does not change, so X-rays can be analyzed over a wide range of wavelengths. The apparatus used for absorption analysis etc. can be simplified.

[Brief explanation of the drawing]

Figure 1 is a diagram of the principle of a flat plate monochromator, Figure 2 is a schematic diagram of an X-ray absorption analyzer using a flat plate monochromator, Figure 3 is a perspective view of a conventional example of a channel cut monochromator, and Figure 4 is a diagram of the principle of a flat plate monochromator. The same plan view,
FIG. 5 is a perspective view showing an embodiment of the X-ray monochromator of the present invention, and FIG. 6 is a plan view thereof. 1... Monochromator, 2... θ rotary plate, 3...
...2θ rotating plate, 4...X-ray source, 5...slit,
6... X-ray detector, 7... Sample, 8... Channel cut monochromator, 9a... First crystal,
9b...Second crystal.

Claims (1)

[Scope of Claims] 1. In a monochromator consisting of first and second crystals having mutually parallel crystal lattice planes, an x-axis with one point on the first crystal lattice plane as the origin, and an x-axis parallel to the lattice plane; An X-ray monochromator characterized in that, when the y-axis is taken perpendicularly, the opposing second crystal surfaces are given by the following formula. 1/x ² + 1/y ² = 4/H ² (H is the distance between the incident X-ray and the spectral X-ray)