JPH06109898A - 2 crystal X-ray monochromator - Google Patents

Abstract

PURPOSE:To embody a two-crystal X-ray monochromator system making selection of an X ray of high monochromaticity possible in a wide wavelength range and making convergence of an X-ray beam possible at a sample position. CONSTITUTION:As to an X-ray beam 1, only an X ray of a wavelength meeting the Bragg rule is diffracted by a first crystal 2 and cast on a second crystal 3. By curving the second crystal 3 to be a cylindrical surface, the X-ray beam 1 falling on the first crystal 2 and a diffracted X-ray beam 4 from the second crystal 3 are made parallel and the X-ray beams made monochromatic can be converged at a sample position. It is possible to make X rays of a wide wavelength band monochromatic and to make them converge so that the intensity of the X rays for a unit area is large at the sample position, and the precision in an analysis of a substance using the X-ray beam and in measured data for a structural analysis can be made high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an X-ray monochromator used in a sample analyzer utilizing X-rays, which is compact and has a wide wavelength band and high accuracy.
It relates to a crystal X-ray monochromator.

[0002]

2. Description of the Related Art A two-crystal X-ray monochromator is a two-crystal X-ray monochromator that rotates and sets a relative positional relationship between the two X-ray beams so that an incident X-ray beam and an outgoing X-ray beam are parallel to each other. It comprises a moving mechanism, a vacuum container for attaching them, an evacuation device, and a control device for controlling the operation of the entire device. When converging at the position of the sample to be irradiated with X-rays, one of the two crystals is curved, or either the incident side or the outgoing side of the X-ray of the two-crystal X-ray monochromator is curved, or both. An X-ray total reflection mirror with a mirror surface is installed to configure the entire system.

In the conventional apparatus, the beam from the X-ray source is diffracted at approximately the center of the first plate crystal, and the crystal position is relatively moved so that the X-ray beam comes to approximately the center of the second plate crystal. The incident X-ray beam and the outgoing X-ray beam are parallel to each other. At this time, setting a condition that the X-ray beam is parallel and does not change the position is disclosed in Japanese Patent Laid-Open No. 61-117436.
Or Oyanagi: PF-Activity Report
As described in (1989) # 7, it becomes a large-sized two-crystal monochromator, and it becomes necessary to control a minimum of four sets of parameters with high precision. In particular, controlling the diffraction angles of two flat plate crystals requires an angle control of 1 second or less, which is extremely difficult.

In such a method, the size of the two-crystal monochromator becomes large, and therefore, when switching the band of the X-ray wavelength for monochromatization, the crystal plate is replaced. In this case, it is necessary to adjust the position of the entire path through which the X-ray beam passes, etc., each time the wavelength band is switched, because the crystal mounting angle is slightly different. Was occurring.

[0005]

According to the present invention, a compact X-ray monochromator capable of converging an incident X-ray beam and an outgoing X-ray beam in parallel and without moving the X-ray beam to a sample position at the same time is realized. By installing this compact X-ray monochromator as a retractable type that can be inserted into the path of multiple sets of X-rays, the wavelength of the X-ray beam incident on the sample can be selected more freely than before and various measurements can be performed. Especially.

[0006]

In order to achieve the above object, the present invention provides a two-crystal X-ray monochromator,
An X-ray beam that is incident at any diffraction angle by matching the rotation axis of the rotary table with the diffraction surface of one crystal surface and controlling the vertical distance from the diffraction surface of the other crystal installed on the same rotation table. The emitted X-ray beam is parallel so that the distance does not change. Further, in order to suppress the intensity of higher-order diffraction lines included in the X-ray beam emitted from the monochromator, the diffraction angles of the two crystals can be set so as to be shifted by several angular seconds, and the higher-order diffraction lines can be suppressed. . Further, the X-ray beam is focused on the position of the sample by adjusting the amount of curvature of one crystal so as to form a cylindrical surface parallel to the X-ray path, depending on the diffraction angle. Multiple monochromators can be installed at the same time by miniaturizing the two-crystal X-ray monochromator by using a small motor that doubles the rotation axis and linearly moves the inner axis to adjust the minute angle and bending amount. And

Further, the inside of the container is evacuated to X by air.
Eliminating the scattering and absorption of the line beam, installing multiple monochromators with different types of attached crystals so that they can be moved back and forth with respect to the X-ray path, enabling monochromaticization from long wavelength to short wavelength X-rays It is a wide band double crystal X-ray monochromator.

[0008]

In the two-crystal monochromator of the present invention, by setting two crystals on the rotary table, the diffraction angle of two crystals can be set with one rotation axis.
A linear moving table that can control the distance between the diffraction planes of two crystals is installed on this rotary table, and a small crystal fine rotation mechanism and a crystal surface curvature adjustment mechanism are installed on the crystal on the rotary table rotation axis. By doing so, the two-crystal monochromator can be controlled with high accuracy. One of the two crystals has a large length in the X-ray beam traveling direction, and X
By controlling the position where the linear beam is diffracted by the linear moving table, it is possible to prevent the position of the monochromatic X-ray beam emitted from the monochromator from changing even if the diffraction angle changes, and by curving one crystal surface, The X-ray beam can be focused on the sample position. In addition, it is necessary to set the diffraction angles of the two crystals by offsetting them by several angle seconds by using the fact that the higher-order diffraction lines included in the X-ray beam emitted from the monochromator are narrower than the angular width of the fundamental wave Can remove higher diffraction lines.

Realizing such a compact and high-precision two-crystal X-ray monochromator, and installing a plurality of monochromators having different crystals or crystal planes and different monochromatic wavelength ranges,
By inserting and using only the monochromator having the wavelength to be used in the path of the X-ray beam, a two-crystal X-ray monochromator system having an unprecedentedly wide wavelength band can be realized. Also, by providing an X-ray shutter for blocking the X-ray beam at the exit side of the monochromator system, it is possible to block the X-rays while maintaining the thermal equilibrium of the crystal of the monochromator, and in particular radiated light is used as the X-ray source. In this case, it is possible to eliminate waste of time required to reach thermal equilibrium.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, 1 is an incident X-ray beam, 2 is a first crystal, 3 is a second crystal, and 4 is an X-ray beam monochromated with two crystals. Reference numeral 5 is a diffraction angle setting motor, 6 is a diffraction angle setting worm gear, 7 is a rotary table, 8 is a second crystal installation table, 9 is a second crystal fine rotation actuator, 1
Reference numeral 0 is a linear movement base of the first crystal, 11 is a movement amount setting motor, and 12 is a first crystal installation base. In the X-ray beam, only the X-ray having a wavelength satisfying the Bragg's law of Expression 1 is diffracted by the first crystal and is incident on the second crystal. By arranging the diffraction planes of the two crystals in parallel, the X-ray beam 1 incident on the first crystal and the diffracted X-ray beam 4 from the second crystal become parallel,
A monochromatic X-ray beam can be extracted.

[0011]

## EQU1 ## 2d.sin .theta. = N..lamda., Where d is the plane spacing of atomic planes for diffracting X-rays, n is the order of diffraction, and .lamda. Is the wavelength of diffracted X-rays.

Next, the movement amount control of the first flat plate crystal so that the incident X-ray beam 1 and the diffracted X-ray beam 4 are parallel and do not move will be described with reference to FIG. When the diffraction angle of the X-ray beam is θ and θ = 30 °, θ = 45 °, and θ = 60 °, 2a, 2b, 2c and 3 in FIG.
It becomes like a, 3b, 3c. Here, assuming that the distance between the perpendicular line passing through the rotation axis of the second crystal 3 and the incident X-ray beam irradiation point 13 on the first crystal 2 is x and the distance between the two crystals is y, where the diffraction angle θ is small. When the distance between the first crystals is controlled so that x is large and y is small, and where the diffraction angle θ is large, x is small and y is large.
It can be seen that and the diffracted X-ray beam 4 are parallel and do not move.

Next, the relationship between x, y and the distance between the incident X-ray beam 1 and the diffracted X-ray beam 4 and l will be described with reference to FIG. When the rotation axis of the second crystal is the origin of coordinates, the coordinates of the incident X-ray beam irradiation point 13 of the first crystal is (x, y).
It is represented by. When the diffraction angle is θ and the relation of each parameter is obtained, it is expressed by the following equation.

[0014]

[Equation 2] l = 2 · y · cos θ

[0015]

## EQU3 ## Therefore, if the position of the first crystal is controlled based on Equation 2, the distance 1 between the incident X-ray beam 1 and the diffracted X-ray beam 4 can be made constant. Since the incident X-ray beam irradiation point 13 moves according to the diffraction angle θ, the size S of the first crystal is required to some extent. The size S and the stroke L of the distance between the two crystals are expressed by Equations 2 and 3, and from the diffraction angle range, Equations 4 and 5
Will be decided respectively.

[0016]

[Equation 4] S = 0.5 · l · (cosec θ ₁ −cosec θ ₂ )

[0017]

Equation 5] L = 0.5 · l · (secθ 2 -secθ 1) Here, theta ₁ and theta ₂ are maximum and minimum values of each diffraction angle. l is 10 mm, θ ₁ and θ ₂ are 80 °, 10 °
Then, S and L are 47.4 mm. The actual size of the first crystal is a value obtained by adding 1/2 of the irradiation width of the incident X-ray beam on the first crystal to this, and when using an incident X-ray beam of 1 mm, about 50.4 mm is required. As a single crystal used in a monochromator, InSb or Si
A crystal having a diameter of at least 3 inches is easily available and can be used as a crystal for a monochromator.

As crystals, InSb (111) and Si (3
11) and Si (771) are used, d of the formula 1 is 0.3740 nm, 0.1602 nm, 0.0, respectively.
Since it is 546 nm, it becomes as shown in the table below from the maximum value and the minimum value of the diffraction angle.

[0019]

Table 1 Crystal λ range (unit: nm) InSb (111) 0.7366 <λ <0.1299 Si (311) 0.3155 <λ <0.0556 Si (771) 0.1075 <λ < As the type of crystal, a general spectroscopic crystal can be used, and KAP, ADP, Ge, GaAs, SiO ₂ , L
It can be selected and replaced according to the resolution of the wavelength such as iF and the wavelength range to be used.

Next, an example of a method of removing higher-order light contained in the diffracted X-ray beam 4 will be described with reference to FIG. As shown in Expression 1, in the diffraction according to Bragg's law, nth-order high-order light is mixed. The n-th higher-order light is the n-th x-ray n
This is one-half the wavelength, and if high-order light is mixed, the S / N of the measurement data deteriorates, which interferes with high-precision measurement. The angular width of diffraction by the flat plate crystal is expressed as the Darwin width (ω) as shown in the following Expression 6.

[0021]

Ω≈8.5 r | F (nk) | tan θ / (πdn ² | k | ² ) where r is the classical radius of the electron, F is the structure factor, and k is the diffraction vector of the diffractive surface. According to the equation 6, the ratio α of ω of the n-th light to the first-order light is expressed by the following equation 7.

[0022]

Α = ω (n) / ω (1) = | F (nk) | / | n ² F (k) | where | F (nk) | / | F (k) | ≦ 1 Therefore, as the order of diffraction increases, the width of diffraction decreases in inverse proportion to the square of the order. Therefore, by shifting the diffraction angles of the first crystal and the second crystal by a small angle Δθ, the intensity of higher-order light contained in the diffracted X-ray beam 4 can be suppressed. The angular distribution of this diffraction intensity is as shown in FIG. This method is called detune and is a simple and effective method for removing higher-order light.

The principle of X-ray focusing will be described with reference to FIG.
The X-ray 1 emitted from the X-ray source 20 is diffracted by the first crystal 2 and is again diffracted by the second crystal 3, and exits the 2-crystal monochromator to reach the sample position 21. At this time, if the second crystal 3 has a cylindrical surface with a radius R, the divergent X-rays emitted from the X-ray source 20 can be focused on the sample position 21. This can be easily understood by assuming a spheroid having two foci as the virtual X-ray source 22 and the sample position 21 when being diffracted only by the second crystal having the cylindrical surface. Here, the distance A between the virtual X-ray source 22 and the second crystal is represented by Equation 8.

[0024]

## EQU00008 ## A = a + l (1 / sin2.theta.-1 / tan2.theta.) A in Expression 8 is the distance from the second crystal to the X-ray source 20. In addition, the distance B is the distance from the second crystal to the sample position 21 which is the focusing point.

The radius R of the cylindrical surface corresponds to the length from the second crystal perpendicular to the second crystal to the intersection of the straight line connecting the virtual X-ray source 22 and the sample position 21. This R is a function of A, B, and θ and is not constant. Now, a straight line connecting the virtual X-ray source 22 and the sample position 21 and the second crystal 3 and the virtual X-ray source 22
If the angle between the straight lines connecting the two is β, then it can be obtained by solving Equations 9 and 10. Equations 9 and 10 are derived from the triangular sine and cosine theorems.

[0026]

[Mathematical formula-see original document] sin β = Bsin2θ / √ (A ² + B ² + 2AB cos2θ)

[0027]

R ² (1-cos ² θ / sin ² β) -2RA sin θ + A ² = 0 where l is 10 mm and a and B are 10 m, Equation 8 shows that θ changes from 10 ° to 80 °. Then almost constant A
= A. In this case, the function of R becomes very simple, and is expressed by Equation 11.

[0028]

Therefore, R changes with θ, and when θ changes from 10 ° to 80 °, it changes with the diffraction angle θ from R = 1376 mm to R = 9848 mm.

FIG. 6 shows a mechanism for realizing this change. The second crystal 3 installed on the second crystal installation table 8 is fixed to the installation table at the central portion of the crystal, and the ends of the crystal are pushed and curved by actuators 30 and 31 having a linear movement mechanism. For the crystal 3 to have a cylindrical surface after being curved, a diamond-shaped crystal 3 having the longest distance in the central portion in the traveling direction of X-rays and the shorter distance toward the end is used. Further, as shown in FIG. 6, in order to improve the accuracy of the cylindrical surface, it has a tooth portion 32 parallel to the traveling direction of the X-ray. If the distance from the center to the end is 30 mm, the distance δ pushed up by the actuators 30 and 31 is approximately represented by the formula 12.

[0030]

Δ (mm) = 900 / (Asin θ) Therefore, when δ changes from 10 ° to 80 °,
It is necessary to change from 0.091 mm to 0.654 mm.

In the present invention, a motor having a double shaft is used as the actuator. This actuator has a structure as shown in FIG. In FIG. 7, the stator 33
The rotor 34 installed inside of the
, And is rotatably movable by a bearing 36. The inner shaft 37 is connected to the outer shaft 35 via a screw portion 38. One end of the inner shaft 37 has a quadrangular shape, and is connected to the motor housing 39 such that the inner shaft 37 cannot rotate but can linearly slide in the axial direction. Therefore, by controlling the rotation of this motor,
The inner shaft 37 slides to become a linear movement actuator. When the amount of change in δ is small, it is possible to use a piezo element, but in the present invention, since an amount of change of about 0.6 mm is required, an actuator using a motor was used. Conventionally, a worm gear or the like has been used to perform similar slide control, but by using the actuator as shown here, it is possible to make the device smaller because no other mechanical portion is required. Further, in the present invention, two actuators are used to bend the second crystal, but it is also possible to do this with one actuator.

As an actuator using such a motor, it is easy to divide one rotation into about 500 by using a stepping motor or a motor with a rotary encoder. Further, it is easy to set the coupling between the inner shaft and the outer shaft with a screw to a module of about 0.25, whereby the relative resolution of linear movement is 0.5.
It can be set to about μm. The greatest feature of this actuator is that the stroke of linear movement can be about 10 mm at the maximum with a small modification of a 30 mm square stepping motor.

FIG. 8 shows a tandem shape of three different monochromatic wavelength bands in which all the X-ray paths of the monochromator are evacuated to a high vacuum from the X-ray source so that X-rays with long wavelengths can also be monochromatically extracted. 2 shows a broadband double crystal monochromator system located at. In this case, the X-ray source is assumed to be radiation emitted from the synchrotron. When the synchrotron radiation is used as an X-ray source, if the radiant light is directly incident on the first crystal, the heat load becomes very large, and even if the first crystal is cooled, the warpage of the crystal and the formation of the first and second crystals. Due to the difference in the lattice constant, etc., it is not possible to obtain a satisfactory monochromatic X-ray. Therefore, a thermal filter 40, which is composed of a filter, a total reflection mirror, etc. and has wavelength selectivity, is installed in front of the monochromator system. Although the X-rays that have passed through the heat filter enter the monochromator, the X-ray source, the heat filter and the monochromator are connected by a vacuum container (not shown), and the whole is kept in a high vacuum.

The three tandem-shaped monochromator units are attached to the vacuum chamber 41 via bellows, and can be independently linearly moved in a direction orthogonal to the X-ray path. is there. The same effect can be obtained by using a movable vacuum seal such as an O-ring instead of the bellows. Control of the monochromatic motor and actuator of each monochromator unit and selection of the monochromator unit are performed by the control device 42. By inputting the required wavelength to the control device, the diffraction angle of the monochromator etc. is automatically set. Parameter setting is performed, and wavelength selection and monochromatic X-ray focusing to the sample position are performed. In this embodiment, InSb (111),
Si (311) and Si (771) are monochromatic crystals, and the wavelength is 0.7 nm as a monochromator system.
It is possible to monochromatize X-rays from 0.0189 nm to X-rays to a sample position with a single system.

Further, in this system, a shutter 4 for blocking X-rays is provided on the sample position side of the monochromator system.
3 are installed. The shutter and the monochromator system are connected by a vacuum container (not shown).
This shutter is used for sample exchange, etc., but by installing it on the sample position side of the monochromator system, the crystal of the monochromator is irradiated with radiant light even when X-rays are blocked by the shutter. By doing this, the sample can be exchanged without breaking the thermal load between the monochromatic crystal due to the synchrotron radiation and the crystal cooling system (not shown), and the measurement can be stabilized immediately by opening the shutter. You can do it.

FIG. 9 shows a cross-sectional view of the joint portion of the vacuum container used in these systems. Since X-rays of synchrotron radiation have a very high intensity, it is necessary to devise them so that they pass through a metal container and then go out. Normally, this metal container is also used as a vacuum container, but the vacuum container has a thin welded joint,
-There are only rings, and X-rays may be emitted into the atmosphere without passing through a given metal thickness. In order to prevent such a situation, conventionally, measures such as covering the whole with a lead plate have been made. However, as shown in FIG. 9, as a fitting type structure, by joining, X-rays can always pass through a metal plate having a predetermined thickness. As a result, X-rays diffracted in a specific direction are emitted into the atmosphere with little attenuation, and it is possible to greatly reduce the number of accidents in which exposure occurs.

[0037]

As described above, the present invention has two advantages.
Compared with a crystal monochromator, X-rays with a wider wavelength band can be monochromated, and the thermal load due to radiant light and the thermal balance of the cooling system can be maintained at all times. Even if the change is made, it is possible to use X-rays for measurement and the like without performing the adjustment requiring a long time. Further, according to the present invention, by curving the second crystal, X-rays can be focused on the sample position in all wavelength regions that can be monochromatic, and a large X-ray intensity per unit area at the sample position can be obtained. It is possible to perform highly accurate measurement. Furthermore, after making the vacuum container of the present invention a fitting type,
Since a vacuum seal such as welding is applied, the amount of X-ray leakage into the atmosphere can be reduced, and the structure is safe with a low probability of accidents due to radiation such as exposure.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a small two-crystal monochromator according to the present invention.

FIG. 2 is a conceptual diagram of position control in which a distance between an incident X-ray beam and an outgoing X-ray beam is constant.

FIG. 3 is an explanatory diagram of a position control method in which a distance between an incident X-ray beam and an outgoing X-ray beam is constant.

FIG. 4 is an explanatory diagram of a high-order light removal method by a detune method.

FIG. 5 is an explanatory diagram of the principle of X-ray focusing by bending the second crystal.

FIG. 6 is an explanatory diagram of a mechanism for bending the second crystal.

FIG. 7 is an explanatory diagram of an actuator according to the present invention.

FIG. 8 is an explanatory diagram of a tandem wide band double crystal monochromator system.

FIG. 9 is a cross-sectional view of a fitting type vacuum container joint.

[Explanation of symbols]

 1 ... Incident X-ray beam, 2 ... First flat plate crystal, 3 ... Second flat plate crystal, 4 ... Monochromatic X-ray beam, 5 ... Diffraction angle setting motor, 6 ... Diffraction angle setting worm gear, 7 ... Rotation Table, 8 ... Second plate crystal installation table, 9 ... Second plate crystal fine rotation motor, 10 ... Linear movement table, 11 ... Movement amount setting motor, 12 ... First plate crystal installation table, 13 ... Incident X X-ray source, 21 ... Sample position, 22 ... Virtual X-ray source, 30 and 31 ... Actuator, 32 ... Second crystal tooth part, 33 ... Stator, 34 ... Rotor, 35 ... 2 Outer shaft of heavy rotation shaft, 36 ... Bearing, 37 ... Inner shaft of double rotation shaft, 38 ... Screw part, 39 ... Motor housing, 40 ... Heat filter, 41 ... Vacuum container, 42 ... Control device, 43 ... X-ray shutter.

Claims (5)

[Claims] 1. An X-ray is diffracted on the surface of one flat plate crystal,
At the same time as the other plate crystal is curved to make the X-ray monochromatic,
In a two-crystal monochromator that converges an X-ray beam at a sample position where a monochromatic X-ray is irradiated, the linear movement of a motor having a double axis is used as a mechanism for adjusting the amount of bending and a minute angle. A 2-crystal X-ray monochromator. 2. A monochromatic wavelength band provided with a moving mechanism capable of inserting and retracting in an X-ray path in a two-crystal monochromator which diffracts X-rays on the surfaces of two crystals and monochromates the X-rays. A two-crystal X-ray monochromator characterized in that a plurality of sets of monochromators of different types are provided in a single vacuum layer. 3. The two-crystal X-ray monochromator according to claim 1 or 2, wherein the path of the X-ray beam is installed in a vacuum container, the diffraction angle of the flat plate crystals, the vertical distance between the diffraction planes of the two flat plate crystals, A two-crystal X-ray monochromator having a mechanism capable of controlling a minute deviation angle from parallel, a bending amount, and a moving mechanism from the outside of the vacuum container. 4. The double crystal X according to any one of claims 1 to 3, wherein an X-ray beam blocking mechanism is provided on a monochromatic X-ray emission side of the double-crystal X-ray monochromator. Line monochromator. 5. The double crystal X-ray monochromator according to claim 1, wherein the vacuum layer of the double crystal X-ray monochromator is fitted with a joint portion and then vacuum-sealed. .