JP2666871B2 - X-ray monochromator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray monochromator used for a focusing optical system in an X-ray analyzer.

[0002]

2. Description of the Related Art Generally, in an X-ray analyzer, X-rays from an X-ray source are focused on a sample, or an electron beam or the like is irradiated on the sample, and X-rays emitted from the sample are focused on a detector. An X-ray monochromator is known as a device of a concentrated optical system such as the one described above. This X-ray monochromator improves the signal / background ratio by allowing only a selected portion of the X-ray radiation to reach the sample or detector, or separates the main line of a double line that cannot normally be separated. This is a device that performs so-called X-ray monochromaticization.

[0003] This method of monochromatization generally uses the dispersion of X-ray energy using diffraction of a dispersive crystal, and is known as Bragg's equation: nλ = 2dsin θ (1) where n = diffraction order, λ = X-ray wavelength, d = lattice plane interval, and θ = Bragg angle.

[0004] As the X-ray monochromator for narrowing or concentrating the X-ray flux, a Johansson monochromator and a Johann monochromator are known from the shape of the spectral crystal used. First, the Johansson monochromator will be described. FIG. 4 is a block diagram of a conventional Johansson type centralized optical system in a Johansson type monochromator.

In FIG. 4, reference numeral 10 denotes a Johansson crystal, r
Is the Rowland circle, O is the center of the curved crystal plane, O ′ is the Rowland circle center, R is the Rowland circle radius, 2θ is the diffraction angle, a,
c is a spectral point and b is a spectral center point. Johansson crystal 1
In the case of 0, the crystal surface is cut out with a curved surface having a radius of 2R of the Rowland circle r and further curved so as to be in contact with the Rowland circle r, thereby forming a spectral crystal.

In this Johansson type monochromator, since all the curved surfaces of the spectral crystal are completely on the Rowland circle r, the spectral center point b which is the center of the spectral crystal and the spectral points b which are both ends of the spectral crystal. The X-rays separated by a and c are completely concentrated on the sample or the slit surface of the detector. In FIG. 4, points A and B are X-ray sources,
Alternatively, it corresponds to the position of the slit surface of the sample or the detector, and all exist on the Rowland circle r.

For example, assuming that point A is an X-ray source and point B is a slit surface of a sample or a detector, the X-rays emitted from point A enter the Johansson crystal 10 at a diffraction angle 2θ at the spectral center point b. , Reach point B on the Roland circle r.
Further, the X-rays emitted from the point A on the Rowland circle r at the spectral point a at the end of the Johansson crystal 10 have a diffraction angle 2θ.
Also reach the point B on the Rowland circle r. Similarly, the X-rays emitted from the point A on the Rowland circle r and incident on the Johansson crystal 10 at a diffraction point 2θ at a spectral point c opposite to the spectral point a at the above-mentioned end also have the same shape as the Rowland circle r. Reach point B above.

Therefore, the X-rays emitted from the point A on the Rowland circle r are separated by the Johansson crystal 10 and all reach the point B on the Rowland circle r and are completely concentrated. Next, the Johann monochromator will be described. FIG. 5 is a configuration diagram of a conventional Johansson type concentrated optical system in a Johann type monochromator.

In FIG. 5, 11 is a Johann crystal, r is a Rowland circle, O is a center of a curved crystal plane, O 'is a Rowland circle center, R is a Rowland circle radius, 2θ is a diffraction angle, and W is Johan's aberration. The Johann crystal 11 is formed by bending a flat plate cut in parallel with the crystal plane at 2R which is twice the radius R of the Rowland circle. At this time, all the curved surfaces of the dispersive crystal do not completely exist on the Rowland circle r. In this Johann monochromator, the separated X-rays are not focused completely on the sample or on the slit surface of the detector, but are approximately concentrated.

[0010]

However, the conventional X-ray monochromator described above has the following problems. (1) The Johansson monochromator using the Johansson crystal has a drawback that, although it satisfies a complete focusing optical system, it is difficult to manufacture the Johansson crystal. (2) In the Johann monochromator using the Johann crystal, all the curved surfaces of the spectral crystal are not completely on the Rowland circle r. Although the X-rays separated at both ends of the crystal are concentrated on the slit surface of the detector, the X-rays are defocused on the sample or the slit surface of the detector, and are approximately concentrated.

[0011] Therefore, this defocus causes a problem in that the analysis sensitivity, the analysis intensity, and the resolution are reduced in the analysis, and it is difficult to measure a minute area. The above problem will be described again with reference to FIG. In FIG. 5, an X-ray emitted from a point A ₂ on the Rowland circle r is incident at a diffraction angle 2θ at a spectral center point P _{2 at} the center of the Johann crystal 11, and reaches a point B ₂ on the Rowland circle r. .

On the other hand, the spectroscopic point a'at the end of the Johann crystal 11
Are the tangents from the spectral point a ′ to the circle C having a radius of 2R cos θ, which satisfies Bragg's equation and the diffraction angle is 2θ.
'. The point A 'and the point B' correspond to the Roland circle r.
It is not the above point. Therefore, for example, an X-ray emitted from the point A ′ and separated at the spectral point a ′ at the end of the Johann crystal 11 is represented by a point B ₃ on the sample or on the Rowland circle r on the slit surface of the detector. To reach the position.

For this reason, the X-rays split at the spectral point a 'at the end of the Johann crystal 11 and the X-rays split at the spectral center point P _{2 at} the center of the Johann crystal 11 are on the Rowland circle r. goal each point B ₃ and point B ₂ next will result in a shift of focus represented by the point which is the difference between B ₃ and point B ₂ W. This shift W is called Johan's aberration.

This Johann aberration W is caused by the Johann crystal 11 when the diffraction angle 2θ is small, or with respect to the Rowland circle r.
Becomes remarkable when is relatively large. This Johan aberration W
Causes a shift in focus, reduces analysis sensitivity, analysis intensity, and resolution in analysis, making it difficult to measure a minute area. The present invention eliminates the above-mentioned problems, and makes it easy to manufacture a spectral crystal, has a small Johan aberration, can obtain a minute focus, and can improve the detection sensitivity and the detection intensity. The purpose is to provide.

[0015]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a Johann type X using a curved dispersive crystal.
In a line monochromator, two or more curved dispersive crystals formed by bending plate-shaped dispersive crystals having different cut-off angles including zero degree at a radius twice the Rowland circle radius are provided, and the cut-off angle of the dispersive crystals is α, and two intersections of one straight line passing through the center of the Roland circle and the Roland circle are defined as O and P2, and a straight line passing through the point O and forming a straight line with the straight line OP2 has the same α as the cutout angle and a Roland circle. When the intersection point other than the point O is P1, the curved dispersive crystals are arranged so that an arbitrary point on the concave surface of each curved dispersive crystal is in contact with the Rowland circle at this point P1. .

[0016]

According to the present invention, (1) the dispersive crystal used for the focusing optical system in the X-ray monochromator can be easily manufactured. (2) It is possible to reduce the Johann aberration of the focusing optical system in the X-ray monochromator and obtain a fine focus. (3) Therefore, the detection sensitivity and detection intensity of the X-ray monochromator can be improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram of the centralized optical system of the X-ray monochromator of the present invention, and FIG. 2 is a configuration diagram for explaining the centralized optical system of the X-ray monochromator of the present invention. 1 and 2, 1 is an asymmetric cut dispersive crystal, 2 is a symmetric cut dispersive crystal, 3 is a flat plate dispersive crystal, O is a curved crystal plane center and a curved center of the symmetric cut dispersive crystal 2, O 'is a Roland circle center, P, P ₁ and P ₂ are the spectral center points, R is the radius of the Roland circle, C, C ₁ and C ₂ are circles, A and B are the points of contact of the circle C from the spectral center point P, A ₁ and B ₁ are circles contacts the spectral center point P ₁ with respect to C _1, a _2, B ₂ is the circle C ₂
Contacts the spectral center point P ₂ for, Y is the crystalline lattice bending center of the asymmetric cut analyzing crystal 1, r is the Rowland circle, l is the crystal lattice plane normal to the flat analyzing crystal 3, l ₁ is for asymmetric cut spectral crystal 1 Plane normal, l ₂ is the crystal lattice plane normal to the symmetric cut spectral crystal 2, m is the normal to the crystal surface of the flat spectral crystal 3, t is the crystal lattice plane, u is the crystal surface,
α is a cutout angle and 2θ is a diffraction angle.

The spectral crystal used in the concentrated optical system of the X-ray monochromator of the present invention is composed of a single crystal in the above-mentioned conventional Johann monochromator, whereas the spectral crystal of the Johann monochromator is composed of a single crystal. It is composed of a plurality of dispersive crystals with different cutout angles of the crystals, and among the plurality of dispersive crystals, the asymmetric cut dispersive crystal 1 is:
The symmetric cut dispersive crystal 2 is bent at a radius 2R about the center O of the curved crystal plane.

First, in order to explain the features of the present invention,
The explanation will be made with reference to the concentrated optical system of the X-ray monochromator of the present invention shown in FIG. The flat plate dispersive crystal 3 shown in FIG. 2 shows a state before the dispersive crystal is bent. In the configuration of the concentrated optical system of the X-ray monochromator of the present invention, as shown in FIG. 1, the flat plate dispersive crystal 3 is composed of an asymmetric cut dispersive crystal 1 curved at a radius 2R centered on a curved center Y and a curved crystal plane. It has a configuration of a symmetric cut dispersive crystal 2 curved at a radius 2R about the center O.

The flat plate crystal 3 has a crystal lattice plane t indicating the direction of the crystal lattice and a crystal surface u indicating the cutting direction of the crystal. Here, the crystal surface u is formed in a linear shape before being curved. A spectral center point P is set at an arbitrary position on the crystal surface u of the flat-plate spectral crystal 3, and the spectral center point P is arranged in contact with the Rowland circle r. Due to the arrangement of the flat dispersive crystal 3, the crystal surface u
The normal m of the crystal surface at the upper spectral center point P passes through the center O ′ of the Rowland circle r and reaches a point Y symmetrical to the spectral center point P of the Rowland circle r. Here, the normal m of the crystal surface is indicated by a broken line in FIG.

A crystal lattice plane normal 1 extending perpendicularly to the crystal lattice plane t from the spectral center point P is indicated by a two-dot chain line in FIG. 2 and passes through the curved crystal plane center O of the Rowland circle r. doing. In this configuration, the cutout angle α of the crystal is the angle formed between the crystal lattice plane t and the crystal surface u,
In FIG. 2, the normal m of the crystal surface and the normal l of the crystal lattice plane
The angle formed by

With the above structure, the X-rays that are spectrally separated while satisfying the Bragg's formula (1) nλ = 2 dsin θ at a diffraction angle 2θ have a curved crystal plane when the crystal lattice plane normal 1 is the center line of reflection. Radius 2R cosαc at center O
It becomes a tangent to the circle C that is osθ. That is, in FIG. 2 , the X-rays are emitted from the contact point A or the contact point B of the circle C toward the spectral center point P on the Rowland circle r of the flat crystal 3 and further from the spectral center point P to the circle C Contact B
Alternatively, the light is dispersed toward the contact point A.

Therefore, by changing the cut-out angle α of the crystal, the Bragg equation (1) n at the diffraction angle 2θ is obtained.
It is possible to change the trajectory of X-rays that disperse while satisfying λ = 2 dsin θ, that is, the position where the spectral X-rays pass on the Rowland circle r. Next, description will be given of a configuration of centralized optical system of the X-ray monochromator of the present invention using an asymmetric cut spectral crystal 1 and symmetrically-cut analyzer crystal 2 by Figure 1.

The asymmetric cut dispersive crystal 1 and the symmetric cut dispersive crystal 2 shown in FIG. 1 are obtained by bending the linear flat plate dispersive crystal 3 shown in FIG. Further, the symmetric cut dispersive crystal 2 is formed by being curved with a radius 2R about the curved crystal plane center O. Symmetric cut spectral crystal 2
Is disposed at a position symmetrical to the spectral center P ₂ with respect to the curved crystal plane center O and the center O of the Rowland circle 'to Rowland circle r, cutting symmetrically to further crystal lattice plane normal to l ₂ Formed out.

On the other hand, the asymmetric cut spectral crystal 1 has its spectral center P ₁ shifted with respect to the center line of the Rowland circle r connecting the center O ′ of the Rowland circle and the center O of the curved crystal plane as shown in FIG. And is formed by being asymmetrically cut out with respect to the normal m ₁ of the crystal surface of the asymmetric cut spectral crystal 1. In FIG. 1, the spectral center P
₁ shows the center line of the Rowland circle r connecting the center O ′ of the Rowland circle and the center O of the curved crystal plane, or the asymmetric cut spectral crystal 1 on only one side with respect to the crystal lattice plane normal l ₂ . Also provided on the opposite side, one concentrated optical system is constituted by a plurality of dispersive crystals of the asymmetric cut dispersive crystal and the symmetric cut dispersive crystal.

Next, referring to FIG. 1, a symmetrical cut dispersive crystal 2
The positional relationship between the X-ray focal point due to and the X-ray focal point due to the asymmetric cut dispersive crystal 1 on the Rowland circle r will be described. First, the focus position of X-rays by the symmetric cut spectral crystal 2 will be described. X-ray diffraction at 2θ Bragg equation (1)
To perform spectroscopy with the symmetric cut dispersive crystal 2 while satisfying nλ = 2 dsin θ, the X-ray has a crystal lattice plane normal l ₂ as a reflection center line, a center at a curved crystal plane center O and a radius of 2
It must be a tangent to the circle C ₂ that is Rcos θ.
The points of contact of this X-ray on the circle C ₂ are point A ₂ and point B ₂
And this contact is on the Rowland circle r.

Next, the focal position of the X-rays by the asymmetric cut spectral crystal 1 will be described. On the other hand, when X-rays are separated by the asymmetric cut dispersive crystal 1 while satisfying Bragg's formula (1) nλ = 2 dsin θ at a diffraction angle of 2θ, the X-rays have a crystal lattice plane normal l ₁ as a reflection center line. , center radius curvature crystal plane center O shall become the tangent of the circle C ₁ is 2R cosαcos θ. This is because the normal m ₁ of the crystal surface and the normal l of the crystal lattice plane depend on the cut-out angle α of the spectral crystal.
_This is because the angle difference α is generated during ₁ . Contacts in the circle C ₁ of the X-ray is indicated by a point A ₁ and the point B ₁ in FIG. 1, this contact is not on the Rowland circle r.

[0028] While the radius of the circle C ₁ is 2R cosαcos θ, a radius of the circle C ₂ is for a 2Rcos θ, between the radius of the circle C ₁ and the circle C ₂ of the circle C ₁ Radius ≦ circle C
There is a relationship of _two radii. The symmetric cut dispersive crystal 2 is
The spectral center point P ₂ can be viewed as part of the conventional Johann crystal to be the same. Therefore, the position where the X-rays separated by the asymmetric cut dispersive crystal 1 intersects the Rowland circle r is more completely concentrated by the Johansson crystal than the position where the X-rays separated by the conventional Johann crystal intersects the Rowland circle r. The position can be made closer to the optical system, and Johan aberration can be reduced.

Next, the above-mentioned asymmetrically cut spectral crystal is used.
The state in which the Johan aberration is reduced is shown in FIG.
Position and the asymmetric cut of the present invention by spectroscopy using crystal
Comparison of focal positions by spectroscopy using spectral crystals
explain. In FIG. 3, O is the center of the curved crystal plane, and O ′ is
Rowland circle center, a is the fraction on the crystal plane of the asymmetric crystal
The light point, a 'is the spectral point on the Johann crystal plane, P₁Is asymmetric
The spectral center point of the crystal, P_TwoIs the spectral center point of the symmetric crystal, and R is
-Land circle radius, C₁, C _TwoIs a circle, A and B are circles C₁To
A ′, B ′ are circles C_TwoAgainst
Contact point from the spectral center point a ', A_Two, B_TwoIs the circle C_TwoAgainst
Spectral center point P_Two, R is the Roland circle, l₁
Is the normal to the crystal lattice plane, and D is the tangent connecting the spectral point a to the contact point B.
The intersection of the extension line and the Rowland circle r, D ', is the spectral point a'
Intersection between the extension of the tangent connecting the contact point B 'and the Roland circle r
It is.

In FIG. 3, the spectral center point P ₁ is the spectral center point on the asymmetric cut spectral crystal of the present invention, and the spectral center point P ₂ is the spectral center point of a conventional Johann crystal (not shown). In addition, it is a spectral center point on the symmetric cut spectral crystal of the present invention. The spectral point a is a spectral point at an end on the asymmetric cut spectral crystal of the present invention, and the spectral point a 'is a spectral point at an end of a conventional Johann crystal (not shown).

X-ray trajectory using conventional Johann crystal
Is a circle C represented by a radius 2Rcos θ. _TwoThe upper contact point A ',
The fraction at the end of a conventional Johann crystal (not shown)
Light point a 'and circle C_TwoIt connects the upper contact point B '.
Then, the X-ray is low on the extension of the contact point B 'as described above.
A focal point is formed at a point D ′ intersecting with the land circle r,
D 'and spectral center point P_TwoFocus on Roland circle r
B_TwoThe Johan aberration W occurs between the two.

On the other hand, the locus of X-rays obtained by spectroscopy using the asymmetric cut dispersive crystal of the present invention has a radius of 2R co
a point A on the circle _{C 1} of Esuarufashioesushita, spectral points a and a circle _{C 2}
It connects the upper contact B. Then, the spectral point a and the circle C
_The focal point D intersecting with the Rowland circle r on the extension of the line segment connecting the contact points B on ₂ substantially coincides with the focal point B2 of the spectrum by the symmetric cut spectral crystal, and the Johan aberration W can be reduced. Further, the spectroscopic point a when the spectral center point P ₁ on the Rowland circle r is focal D is exactly matches the focal point B ₂ of spectroscopy with symmetrical cut analyzer crystal.

Therefore, by using a plurality of light-separating crystals having different cutting angles α according to the present invention, the Johan aberration W can be reduced as compared with the case where a conventional Johan crystal is used. In the above embodiments, the so-called single vent, in which the curve of the dispersive crystal is cylindrically curved along the Rowland circle, has been described. It is also possible.

That is, at one point on the Roland sphere,
The X-rays reflected on the Roland sphere can be concentrated, and the detection intensity can be further improved. It should be noted that the present invention is not limited to the above embodiments, and various modifications are possible based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0035]

As described above, according to the present invention, (1) it is possible to provide a Johann monochromator constituted by a spectral crystal which is easy to manufacture. (2) It is also possible to provide a Johann monochromator capable of obtaining a fine focus by reducing Johan aberration and improving detection sensitivity and detection intensity.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a concentrated optical system of an X-ray monochromator of the present invention.

FIG. 2 is a configuration diagram for explaining a concentrated optical system of the X-ray monochromator of the present invention.

FIG. 3 is a comparison diagram of a focus position by spectroscopy using a conventional Johann crystal and a focus position by spectroscopy using an asymmetric cut spectral crystal of the present invention.

FIG. 4 is a configuration diagram of a conventional Johansson type centralized optical system in a Johansson type monochromator.

FIG. 5 is a configuration diagram of a conventional Johansson type concentrated optical system in a Johann type monochromator.

[Explanation of symbols]

1 ... Asymmetric cut spectral crystal, 2 ... Symmetric cut spectral crystal,
3: flat plate crystal, O: center of curved crystal plane, center of curvature of symmetric cut crystal 2, O ': center of Rowland circle, P, P
₁ , P ₂ ... Spectral center point, R ... Roland circle radius, C, C
₁ , C ₂ ... Circle, A , B... Contact point from spectral center point P or a to circle C or C ₂ , A ′ , B ′... Contact point from spectral center point a ′ to circle C ₂ , A ₁ , B ₁ ... contact from the spectral center point _{P 1} with respect to the circle _{C 1, a 2, B 2} ... circle C also
Contacts the spectral center point P ₂ is for C _2, Y ... asymmetric cut spectral crystal 1 of the bending center, r ... Rowland circle,
1 ₁ , 1 ₂ ... normal to crystal lattice plane, m ... normal to crystal surface, t
... Crystal lattice plane, u ... Crystal surface, α ... Cutting angle, 2θ ...
Diffraction angles, a , a '... spectral points .

Claims (1)

(57) [Claims] 1. In a Johann X-ray monochromator using a curved spectral crystal, a flat spectral crystal having a cutout angle different from each other including zero degree has a Roland circle radius of 2 mm.
Two or more curved dispersive crystals formed by bending with a double radius are provided, the cutout angle of the dispersive crystals is α, and two intersections of one straight line passing through the center of the Roland circle and the Roland circle are O and P2. When an intersection point other than the point O between the straight line passing through the point O and the straight line OP2 having the same α as the cutout angle and the Rowland circle is defined as P1, an arbitrary point on the concave surface of each curved dispersive crystal is obtained. Wherein each curved dispersive crystal is disposed so as to be in contact with the Rowland circle at this point P1.