JPH11295499A - Johannson-type analyzing crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the necessity to use thick crystals, enable the expansion of a solid angle and easily realize asymmetrical crystals by constituting a crystal-mounting seat having a plurality of cylindrical surfaces formed in stairs. SOLUTION: On the mounting surface of a crystal seat 1, crystal-mounting surfaces which constitute sections of a cylindrical face respectively are shaped like stairs. That is, four crystal mounting surfaces P1 , P2 , P3 and P4 are formed like stairs. Consequently, it is sufficient if only the difference in curvature radiuses of cylindrical face sections is set equal to the thickness of each crystal to be stuck on each crystal-mounting surface, so it is not required to increase the thicknesses of the crystals as they come away from the center of a spectrum, and a problem of difficulty in curvature processing does not occur. Moreover, analyzing crystals are symmetrized to the center 0 of the spectrum, but asymmetrical crystals can be made by using a part of them, and analyzing crystals having a center of a spectrum outside a crystal face can be also formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a Johansson-type dispersive crystal.

[0002]

2. Description of the Related Art A Johansson-type spectroscopic crystal is used in an electron probe microanalyzer (EPMA) or the like. Conventionally, as shown in FIG. Is formed by bending a crystal 2 on a crystal mount 1 formed as a part of a cylindrical surface of 2R, and cutting the crystal along a cylindrical surface having a radius of curvature R.

[0003]

However, since the conventional Johansson-type dispersive crystal has only one mounting surface for the crystal, if the solid angle of X-ray incidence on the dispersive crystal is increased, the crystal becomes farther away from the spectral center. However, there is a limit in naturally processing such a thick crystal by bending it, and it is difficult to increase the solid angle.

In particular, when the X-ray incidence angle is small and the distance between the X-ray generation point and the spectral crystal is small, the spectral center does not coincide with the center of the crystal surface.
It is desirable to use an asymmetric crystal shifted to the primary particle beam side as shown in (1), and it is known that the spectral characteristics are improved by using such an asymmetric crystal. As shown in FIG. 8, it is necessary to remarkably increase the thickness of the crystal away from the primary particle beam. However, as described above, it is difficult to bend a thick crystal, and it is very difficult to realize an asymmetric crystal.

Accordingly, an object of the present invention is to provide a Johansson-type spectroscopic crystal which does not need to use a thick crystal, can increase the solid angle, and can easily realize an asymmetric crystal. It is.

[0006]

In order to achieve the above object, in a Johansson type crystal according to the present invention, a crystal mounting surface of a crystal mounting base has a plurality of cylindrical surface portions having a predetermined radius of curvature having predetermined heights. The step is formed in a step-like manner in the step, and the crystal is attached to the crystal attachment surface formed in the step-like shape.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a cross section of an embodiment of a Johansson type crystal according to the present invention. On a mounting surface of a crystal mounting base 1, a plurality of crystal mounting surfaces each forming a part of a cylindrical surface are stepped. Is formed. FIG. 1 (a)
In the figure, four crystal mounting surfaces P ₁ , P ₂ , P ₃ and P ₄ are formed stepwise. In FIG. 1A, the cylindrical surfaces forming the _four crystal mounting surfaces P ₁ , P ₂ , P ₃ , and P ₄ are concentric. Therefore, when the difference between the radius of curvature of the cylindrical surface portion forming the crystal mounting surface adjacent the r, the first crystal mounting surface P ₁ is intended to be part of the cylindrical surface of radius of curvature 2R, the second crystal mounting surface P ₂ is the radius of curvature (2R-r)
, The third crystal mounting surface P ₃ forms a part of a cylindrical surface having a radius of curvature of (2R−2r), and the fourth crystal mounting surface P ₄ has a radius of curvature of (2R−2). 3r) is a part of the cylindrical surface. In the drawing, O indicates a spectral center. R is the radius of the Roland circle. This is the same in the following.

In the case of forming a spectral crystal, FIG.
The crystal mounting surfaces P ₁ and P 1 of the crystal mounting table 1 shown in FIG.
_2, P _3, the P _4, the crystal K ₁ as shown in FIG. 1 (b),
K ₂ , K ₃ and K ₄ are pasted, and these crystals K ₁ , K
₂ , K ₃ , and K ₄ may be cut along a cylindrical surface having a radius of curvature R as shown by a broken line in FIG.

As described above, according to this Johansson-type spectral crystal, the thickness of the crystal attached to each crystal mounting surface may be all r, and it is not necessary to increase the thickness as the distance from the spectral center increases as in the conventional case. Therefore, the above-described problem of difficulty in bending processing does not occur. In FIG. 1, the spectral crystal is symmetrical with respect to the spectral center O. However, as shown in FIG. 1D, an asymmetric crystal or a spectral crystal having no spectral center in the crystal plane is manufactured using only a part thereof. It is also possible.

Next, the design of the crystal mount 1 will be described. Here, the case of designing a crystal mounting base having three crystal mounting surfaces shown in FIG. 2 is considered. In FIG. 2, the cylindrical surfaces forming the three crystal mounting surfaces are concentric, and the difference between the radii of curvature of the cylindrical surface portions forming the adjacent crystal mounting surfaces is r.

When the xy orthogonal coordinates are set with the spectral center O as the origin, in order to design the crystal mount, Q
₁ the coordinates of the eight points to Q ₈ may knowing. Q ₁ is the right end point of the first crystal mounting surface, Q ₂ is the left end of the second crystal mounting surface, Q ₃ is the right end of the second crystal mounting surface,
₄ is the left end of the third crystal mounting surface. In FIG. 2, Q ₁ and Q ₅ , Q ₂ and Q ₆ , Q ₃ and Q ₇ , Q ₄ and Q
₈ are each symmetric about the y-axis.

In this case, as shown in FIG.
_0, consider the _{C 1, C 2, C 3} . The circle C ₀ is a circle defining a crystal plane, the radius is R, and the center is (0, R).
The circle C ₁ is a circle that defines the first crystal mounting surface, and has a radius of 2R and a center of (0, 2R). Circle C ₂ is the circle defining the second crystal mounting surface, the radius (2R-r),
The center is (0,2R). Circle C ₃ is a circle defining the third crystal mounting surface, the radius (2R-2r), the center is (0,2R). Therefore, each circle C ₀ , C ₁ , C ₂ ,
Equation of C ₃ are as respectively (1) to (4).

X ² + (y−R) ² = R ² (1) x ² + (y−2R) ² = (2R) ² (2) x ² + (y−2R) ² = (2R− r) ² ... (3) x ² + (y−2R) ² = (2R−2r) ² ... (4) First, since the point Q ₂ is the intersection of the circle C ₀ and the circle C ₂ , the point Q ₂ Can be obtained by solving the simultaneous equations of equations (1) and (3). Then, the coordinates of the point Q ₂ are represented by (x ₂ ,
y ₂ ), the point Q ₁ is the intersection of the circle C ₁ and the perpendicular drawn from the point Q ₂ to the x-axis, so that the coordinates of the point Q ₁ are (x ₁ ,
If y _{1) to, x 1 = x 2 ... (} 5) y 1 = - ((2R) becomes _{^{2 -x 2 2) 1/2 + 2R}} ... (6). Similarly, since the point Q ₄ are the intersection of the circle C ₀ and the circle C _3, the coordinates of the point Q ₄ can be obtained by solving the simultaneous equations (1) and (4). Then, when the coordinates of the point Q ₄ and (x _4, y _4), since the point Q ₃ is a vertical line and the intersection of circle C ₂ drawn from the point Q ₄ on the x-axis, the coordinates of the point Q ₃ (x
_3, when y _{3) that, x 3 = x 4 ... (} 7) y 3 = - ((2R-2r) becomes _{^{2 -x 4 2) 1/2 + 2R}} ... (8). Thus the coordinates of Q ₁ to Q ₄ are determined. Therefore, it is possible to determine easily the coordinate of Q ₅ to Q ₈ in FIG. These points Q _{5 to} Q ₈ are Q _{1 to} Q ₄
And the y-axis.

As described above, since the coordinates of all the points Q _{1 to} Q _{8 in} FIG. 2 are obtained, the crystal mounting base can be designed.

In the above, the case where the cylindrical surfaces forming the respective crystal mounting surfaces are concentric has been described, but it is also possible to make the radii of curvature of the respective crystal mounting surfaces the same. The design of the crystal mounting base in that case will be described. Here, it is assumed that the center positions of the cylindrical surface portions forming adjacent crystal mounting surfaces have a difference of r in the y-axis direction. Here, the spectral center O
Only one side will be described.

Taking the xy orthogonal coordinates with the spectral center O as the origin, as shown in FIG. 4, four circles C ₀ ′, C ₁ ′, C
Consider ₂ ′ and C ₃ ′. The circle C ₀ ′ is a circle defining the crystal plane, the radius is R, and the center is (0, R). Circle C ₁ ′
Is a circle defining the first crystal mounting surface, the radius of which is 2
R, center is (0,2R). The circle C ₂ ′ is a circle defining the second crystal mounting surface, and has a radius of 2R and a center of (0, 2R + r). The circle C ₃ ′ is a circle defining the third crystal mounting surface, the radius is 2R, and the center is (0, 2R
+ 2r). Therefore, each circle C ₀ ′, C ₁ ′, C ₂ ′,
The equations for C ₃ 'are as shown in (9) to (12), respectively.

X ² + (y−R) ² = R ² (9) x ² + (y−2R) ² = (2R) ² (10) x ² + (y− (2R + r)) ² = ( 2R) ² ... (11) x ² + (y− (2R + 2r) ² = (2R) ² ... (12) First, the point Q ₂ ′ is the intersection of the circle C ₀ ′ and the circle C ₂ ′. The coordinates of Q ₂ ′ can be obtained by solving the simultaneous equations of equations (9) and (11), and if the coordinates of point Q ₂ ′ are (x ₂ ′, y ₂ ′), the point Q 'because it is the intersection of the point Q _{1' 1} 'is the point Q _2' perpendicular and the circle C ₁ drawn in the x-axis from the coordinates of (x ₁ ', y _1') When, x ₁ '= x _{2 '... (13) y 1'} = - a _{^{((2R) 2 -x 2 '}} 2) 1/2 + 2R ... a (14) Similarly, the point Q _4.' is the circle C ₀ 'and the circle C _3' , The coordinates of the point Q ₄ ′ can be obtained by solving the simultaneous equations of the equations (9) and (12). , Point Q ₄ ′
Is (x ₄ ′, y ₄ ′), the point Q ₃ ′ becomes the point Q ₄ ′
Is the point of intersection of the perpendicular drawn to the x-axis and the circle C ₂ ′, and if the coordinates of the point Q ₃ ′ are (x ₃ ′, y ₃ ′), x ₃ ′ = x ₄ ′ (15) y ₃ '= - ((2R-2r ) 2 -x 4' becomes ^{2) 1/2 + 2R ... (16} ). Thus, the coordinates of Q ₁ ′ to Q ₄ ′ are obtained. From this, the point on the opposite side of the y-axis can be easily obtained from the symmetry condition.

Since the coordinates of Q ₁ ′ to Q ₄ ′ are obtained as described above, a crystal mounting table as shown in FIG. 5 can be designed. In FIG. 5, P ₁ ′ is the first crystal mounting surface, which is defined by a part of the circle C ₁ ′ in FIG. P ₂ ′ and P ₃ ′ are second and third crystal mounting surfaces, respectively, which are defined by parts of circles C ₂ ′ and C ₃ ′ in FIG.

As described above, in this Johansson-type dispersive crystal, it is not necessary to increase the thickness of the Johansson-type dispersive crystal further away from the spectral center as in the prior art, so that the above-described problem of difficulty in bending processing does not occur. is there. FIG.
In FIG. 1, the spectral crystal is symmetrical with respect to the spectral center O. However, as shown in FIG. 1D, it is also possible to form an asymmetrical crystal using only a part thereof.

According to the Johansson-type spectral crystal, an asymmetric crystal as shown in FIG. 1D can be realized, so that the X-ray extraction angle α can be made larger than that of the conventional EPMA. it can. That is, in a so-called vertical spectroscope in which the Rowland circle surface is perpendicular to the sample surface, which is widely used in the past, the X-ray incident angle θ to the spectral crystal is X
If the X-ray detection angle is larger than the angle α, the X-ray detector will be positioned below the consideration plane, and the X-ray detector may collide with the sample.
Therefore, in order to prevent interference with a large θ, it is necessary to increase the X-ray extraction angle α. However, if (a) is increased, then the spectral crystal will interfere with the electron gun. However, if an asymmetric type of dispersive crystal as shown in FIG. 1D is used, a plurality of crystals can be simultaneously arranged, for example, as shown in FIG. 6, so that the X-ray extraction angle α is substantially reduced. It can take up to around 90 ° and X
The X-ray detector is not located below the sample surface even if the line incident angle θ is set to near 90 °.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a Johansson-type spectral crystal according to the present invention.

FIG. 2 is a diagram for explaining the design of a Johansson-type spectral crystal according to the present invention.

FIG. 3 is a diagram for explaining an example of a method of designing the Johansson-type spectral crystal shown in FIG. 2;

FIG. 4 is a diagram for explaining another example of a method of designing a Johansson-type spectral crystal.

FIG. 5 is a diagram showing an example of a Johansson-type spectral crystal created by the design method shown in FIG.

FIG. 6 is a diagram for explaining an effect of the present invention.

FIG. 7 is a diagram showing an example of a conventional Johansson-type spectral crystal.

FIG. 8 is a diagram showing an example of an asymmetric crystal.

[Explanation of symbols]

 1. Crystal mounting base.

Claims (1)

[Claims] 1. A crystal mounting surface of a crystal mounting table, wherein a plurality of cylindrical surface portions having a predetermined radius of curvature are formed in steps with a predetermined height in steps, and the crystal mounting surface is formed on the crystal mounting surface formed in steps. A Johansson-type spectroscopic crystal characterized by being attached with.