JPH0762720B2 - Double crystal X-ray spectrometer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a double crystal X-ray spectroscope, and more particularly to a double crystal X-ray spectroscope using a flat type dispersive crystal.

[Conventional technology]

In recent years, there has been a strong demand for establishment of a structural analysis technique for substances using X-rays. In this type of analysis, the X-ray transmittance is changed for each set wavelength by changing the X-ray wavelength within a certain range. , Fluorescent X-ray yield, secondary electron yield or diffracted X-ray intensity and the amount thereof are measured.

For this purpose, it is necessary to have a technique for spectrally analyzing only the X-ray component of a desired wavelength from continuous wavelength components obtained from an electron beam excitation type X-ray generator, a synchrotron radiation source, etc. To reduce systematic error, X
There is an urgent need to develop a spectroscopic optical system that has a high wavelength setting accuracy for lines and that allows easy adjustment of the optical axis for easy handling.

Here, the operation principle of the double crystal X-ray spectrometer using the flat dispersive crystal will be described with reference to FIG. In FIG. 2, an X-ray having a continuous wavelength emitted from the X-ray generation source 1 is diffracted by the first dispersive crystal 2 and goes to the second dispersive crystal 3. Since the X-ray diffraction by the crystal follows Bragg's law, the crystal plane spacing of the first dispersive crystal 2 is d, the incident angle of the X-rays with respect to the crystal plane of the first dispersive crystal 2 is θ, and the second spectroscopic crystal is If the wavelength of X-rays going to the crystal 3 is λ,
Bragg's law n λ = 2d sin θ (1) holds. Here, n is a natural number called the Bragg order.

In such a two-crystal X-ray spectroscope, when the second dispersive crystal 3 is not provided and there is only one dispersive crystal, a so-called single-crystal X-ray spectroscope is used. Crystal 2
The direction of the diffracted X-ray from is the wavelength of the diffracted X-ray, that is,
It changes each time the incident angle θ of the X-ray with respect to the first dispersive crystal 2 is changed, and restricts the structure of the measurement system. Further, in a single crystal X-ray spectrometer, generally, X-rays having a desired wavelength, that is, the first (1)
In addition to the case of n = 1 in the formula, harmonic X-rays, that is, n ≧ 2
In the case of, the X-ray is also included, which often causes an increase in systematic error in the measurement data.

The second dispersive crystal 3 is installed in order to eliminate such a drawback of the single crystal X-ray spectroscope, and when the incident angle of X-rays on the first dispersive crystal 2 is θ, the second dispersive crystal 3 is provided. The angle for the X-ray diffracted by the first dispersive crystal 2 is also set to the same θ. At the same time, the distance between the incident X-ray and the extension line of the diffraction X-ray by the second dispersive crystal 3 is set to L, and x = LCot from the intersection point of the perpendiculars drawn from the rotation center of the first dispersive crystal 2 to the extension line. (2θ) The second dispersive crystal 3 is moved to the position x that satisfies (2). Here, x> 0 is the opposite side of the X-ray generation source 1 when viewed from the above intersection, x
<0 is on the X-ray generation source 1 side when viewed from the above intersection. If the first dispersive crystal 2 and the second dispersive crystal 3 are arranged at positions satisfying the expression (2), the emission direction of the diffracted X-rays from the second dispersive crystal 3 remains unchanged.

Further, by utilizing the fact that the shorter the wavelength of the X-ray is, the narrower the half-value width of the diffracted X-ray intensity is, the set angle of the second dispersive crystal 3 is intentionally set to 1 to 10 angular seconds from the set angle θ of the first dispersive crystal 2. By shifting it, the intensity of the diffracted X-rays from the second dispersive crystal 3 becomes 40
Set it to be ~ 60%. As a result, 95% or more of high-order harmonic components can be removed.

This type of device is used by S. Khalid et al.
R.Emrich, R.Dujari J.Shultz, and JRKatzer), Laboratory EXAFS for Catalysis Research
spectrometer for catalyst studies), Review of Scientific Instruments (Rev.Sc
i.Instr.), 53 (1) (1982), PP22-33, JP-A-60-8645
No. 5, etc.

[Problems to be solved by the invention]

However, in the above-mentioned two-crystal X-ray spectroscope, in order to make the diffraction direction of the diffracted X-rays from the second dispersive crystal 3 constant regardless of the incident angle of the incident X-rays to the first dispersive crystal 2, Only when the arrangement of the second dispersive crystals 2 and 3 is ideally adjusted. That is, a vector perpendicular to the crystal plane of the first dispersive crystal 2, that is, a normal vector, and the second dispersive crystal 3
Both normal vectors of the
It must be included in the plane defined by the line segment connecting the centers of the dispersive crystals 3 and the X-ray axis incident on the first dispersive crystal 2.

If these adjustments are not sufficient, the diffraction direction of the diffracted X-rays by the second dispersive crystal 3 will not be constant, and the wavelength of the monochromatic X-ray obtained from the double-crystal X-ray spectroscope will not be the same. Since it deviates from the equation (1), the systematic error of the measurement data is increased.

The x-axis is the direction in which the X-rays emitted from the X-ray source travel, and the z-axis is the vertically upward direction. The y-axis is the direction orthogonal to the x-axis and z-axis in the horizontal plane and forming the right-handed coordinate system. When the center of rotation of the first dispersive crystal 2 is set as the origin of coordinates, the set angle of the first dispersive crystal 2 is −θ ₁ , and the normal vector of the crystal plane of the first dispersive crystal 2 is set as shown in FIG. The angle formed by and the xz plane (this is referred to as a tilt angle. The same applies to the case of the second dispersive crystal 3) is set to ₁ . Here, the angle is taken counterclockwise to be positive. Similarly, the set angle of the second dispersive crystal 3 is set to −.
Let θ _{2 be 2} and the angle between the normal vector of the crystal plane of the second dispersive crystal 3 and the xz plane. However, ₁ and ₂ are assumed to satisfy | ₁ | ≤ 0.01 rad, | ₂ | ≤ 0.01 rad (3).

At this time, the direction vector of the x-rays diffracted by the first analyzing crystal 2 ignores the ^{_{φ 1 2, (Cos2θ 1,}} -2 1 Sinθ 1, - (1- 1 2) Sin2θ 1)
(4) and the wavelength λ of the diffracted X-ray is Becomes To diffract the X-ray diffracted by the first dispersive crystal 2 by the second dispersive crystal 3, Must satisfy the diffraction conditions of. When the formula (6) is satisfied, the direction vector of the X-ray diffracted by the second dispersive crystal 3 ignores ₁ ² , _{1 2} and ₂ ² (1,2 ( ₂ , ₁ ) Sinθ ₁ , 0) … (7).

Therefore, the X-ray detector 4 at (l, 0, -L) in FIG.
, The X-ray position is in the y-axis direction. It just shifts. The wavelength λ set by λ = 2d Sin θ ₁
By Only X-rays with a short wavelength can be obtained.

Therefore, to ensure that X-rays can be incident on the X-ray detector 4 and to accurately determine the wavelength, the tilt angles ₁ and ₂
As small as possible (practically │ ₁ |, | ₂ ｜ <10 ^-3 r
ed).

However, the conventional apparatus has not been able to easily adjust the tilt angles ₁ and ₂ and requires skill and a lot of time.

That is, in the prior art, means for easily adjusting the tilt angle of the dispersive crystal is not provided, skill and a lot of time are required for adjusting the tilt angle, and it is difficult to adjust to the required accuracy. There is a drawback that an error occurs in the wavelength of the X-rays obtained by spectral separation and the systematic error of the acquired data cannot be reduced.

It is an object of the present invention to provide a double crystal X-ray spectroscope with an automatic optical axis adjusting mechanism that facilitates the adjustment of the tilt angle of the dispersive crystal and has a high X-ray wavelength setting accuracy.

[Means for solving problems]

The structure of the present invention taken to solve the above-mentioned problems is a first flat-plate type dispersive crystal having a center of rotation on an X-ray beam emitted from an X-ray source and made parallel, and the first flat plate. The X-ray beam diffracted by the X-ray type dispersive crystal is incident, and the diffracted X-ray is emitted from the X-ray source and emitted in a direction parallel to the incident X-ray beam. A two-crystal X-ray spectroscope having a second flat-plate type dispersive crystal having a center of rotation on the diffracted X-ray beam, wherein each of the first and second flat-plate dispersive crystals is provided. Rotating means for setting the diffraction angle and tilting angle adjusting means for adjusting the tilting angle, and a dispersive crystal for setting the distance between the first flat-plate type dispersive crystal and the second flat-plate dispersive crystal. Interval setting means and X diffracted by the second flat dispersive crystal A position-sensitive X-ray detector provided on the axis, and the rotation means and the tilt angle of the first and second flat-plate type dispersive crystals using the detection results of the position-sensitive X-ray detector. An adjusting means and a means for controlling the dispersive crystal spacing setting means are provided.

As a dispersive crystal, depending on the X-ray wavelength band used, Bery
Although various crystal faces such as l, InSb, and Si having desired orientations are taken out and polished, a diffraction grating may be used depending on the case.

As a mechanism for rotating the dispersive crystal, there are a method using a gear, a method using a chain, a method using a friction wheel, and the like, but it is preferable to use the gear in terms of processing accuracy and reliability.

As a mechanism for adjusting the tilt angle of the crystal, there are a method of rotating a micrometer with a motor having a speed reduction mechanism and a method of using a piezo element.

As a position-sensitive X-ray detector, a method of using a photodiode with a small effective diameter, or a slit or the like is provided in an X-ray receiver such as an ion chamber, a scintillation counter, or a solid-state detector (SSD). The effective diameter may be reduced and used.

[Action]

In the double crystal X-ray spectrometer of the present invention, a slit for limiting the width of X-rays is arranged on the X-ray axis emitted from the X-ray generation source,
A first dispersive crystal having a rotation mechanism having a center of rotation on the X-ray axis of the X-rays passing through the slit and a tilt angle adjustment mechanism is disposed, and a second dispersive crystal on the X-ray axis of the X-rays diffracted by the first dispersive crystal.
An X-ray axis of the X-ray diffracted by the second dispersive crystal is provided by disposing a second dispersive crystal having a rotation mechanism and a tilt angle adjusting mechanism on a gantry having a moving mechanism that makes the diffracted X-ray from the dispersive crystal immobile. A position-sensitive X-ray detection device is arranged on the top.

Therefore, in order to adjust the tilt angle of the dispersive crystal with this double crystal X-ray spectroscope, first, the first dispersive crystal is set to an angle Θ ₁ close to 45 degrees, and the gantry is moved to use the first dispersive crystal. Diffraction X
The center of rotation of the second dispersive crystal is placed on the X-ray axis of the line. After that, the rotation angle and the tilt angle of the second dispersive crystal are adjusted so that the X-ray diffracted by the second dispersive crystal enters the position-sensitive X-ray detector. Next, the setting angle of the first dispersive crystal is set as low as possible Θ ₂ , and the gantry is moved so that the rotation center of the second dispersive crystal comes on the X-ray axis of the X-ray diffracted by the first dispersive crystal. To do. Subsequently, the rotation angle of the second dispersive crystal and the tilt angle of the first dispersive crystal are adjusted so that the X-rays diffracted by the second dispersive crystal enter the position-sensitive X-ray detector.

By repeating such a procedure, the deviation of the tilt angles of the first and second dispersive crystals gradually approaches 0, and by repeating about 25 times, it is possible to obtain about 10 ⁻³ rad.
Along with this, the relative error of the obtained X-ray wavelength is also suppressed to about 10 ^−6, so that the systematic error of the measurement data can be reduced.

〔Example〕

 Examples will be described below.

FIG. 1 is an explanatory view of one embodiment, the same parts as those in FIG. 2 are denoted by the same reference numerals, 5 is a spectrometer container having X-ray passages 5a and 5b, and 6 is provided in the X-ray passage 5a. The slit,
7, 8 and 9 are a micrometer for the first dispersive crystal 2, a diffraction angle setting motor, a tilt angle adjusting motor,
10 is a mount for the second dispersive crystal 3, 11 is a ball screw for driving the mount 10 by a mount moving motor 12, and 13, 14 and 15 are
A micrometer for the second dispersive crystal 3, a diffraction angle setting motor, a tilt angle adjustment motor, 16 is a magnetic fluid seal provided at the mounting portion of the spectroscope container 5 of the gantry moving motor 12, and 17 is a magnetic fluid seal. The slit 18 provided in the X-ray passage 5b has an input end connected to the X-ray detector 4 and an output end connected to the first end.
It is connected to the diffraction angle setting motor 8 for the dispersive crystal 2, the tilt angle adjusting motor 9, the diffraction angle setting motor 14, the tilt angle adjusting motor 15, and the gantry moving motor 12 for the second dispersive crystal 3. The control unit is shown.

FIG. 4 is an explanatory view of the configuration of the tilt angle adjusting means, and 19 is a drive unit of the tilt angle adjusting means, to which the tilt angle adjusting motor 20 and the micrometer 21 are attached, and the worm wheel 2
2, 23 are used to operate the micrometer 21. Reference numeral 24 is a crystal holder to which a dispersive crystal 26 is fixed by a leaf spring 25. The crystal holder 24 is attached to the drive unit 19 by a spring 27, one end is held by a knife edge 28 and the other end is held by a micrometer 21, and a micrometer. The tilt angle can be adjusted by moving 21.

In this embodiment, X-rays having a continuous spectrum generated by the X-ray generation source 1 are incident on the first dispersive crystal 2 after passing through the slit 6 through the X-ray path 5a and a part of the incident X-rays, that is, , X-rays having a wavelength satisfying the Bragg condition are diffracted by the first dispersive crystal 2. The X-rays diffracted by the first dispersive crystal 2 are again diffracted by the second dispersive crystal 3 to produce X-rays.
X-ray detector 4 after being guided to the line path 5b and passing through the slit 17
Be led to.

In this case, the X-ray generation source 1, the first dispersive crystal 2 and the second dispersive crystal 3, and the first dispersive crystal 2, the second dispersive crystal 3 and the X-ray detector 4 each have a positional relationship satisfying the Bragg condition. It has become.

The diffraction angles θ ₁ and θ ₂ of the first dispersive crystal 2 and the second dispersive crystal 3 are respectively set through the speed reducing mechanism to the diffraction angle setting motor 8 for the first dispersive crystal 2 and the diffraction angle setting motor 14 for the second dispersive crystal 14. Set by.

The tilt angle _{1 of} the first dispersive crystal 2 and the second dispersive crystal 3 and
₂ is adjusted by rotating the micrometers 7 and 13 respectively by the tilt angle adjusting motor 9 of the first dispersive crystal 2 and the swing angle adjusting motor 15 of the second dispersive crystal 3.

The mount 10 on which the second dispersive crystal 3 is mounted is a double crystal X.
It is moved from a gantry moving motor 12 provided outside the container 5 of the line spectrometer through a magnetic fluid seal 16 and a ball screw 11 introduced into the container 5.

The controller 8 drives the diffraction angle setting motors 8 and 14, the tilt angle adjusting motors 9 and 15, and the gantry moving motor 12.
The controller 18 can also process the output signal from the X-ray detector 4.

Next, a method for adjusting the tilt angle of the dispersive crystal in this example will be described.

Let L be the rotation center of the first dispersive crystal 2 and the distance from this rotation center to the intersection of the perpendicular line drawn on the extension line of the diffraction X-ray by the second dispersive crystal 3, and let the diffraction X by the second dispersive crystal 3 from the intersection. The distance to the X-ray detector 4 arranged on the X-ray axis of the line is l. In this embodiment, L = 190 mm, l = 2,500
mm.

The width of the slit 6 for limiting the X-ray width is set to about 1 mm, and the effective diameter of the X-ray detector 4 installed at the X-ray source side position of the light-receiving surface of the X-ray detector 4 is narrowed down. Slit
The width of 17 is also about 1 mm.

To adjust the tilt angle ₂ of the first analyzing crystal 2 of tilt angle ₁ and the second analyzing crystal to about 10 ^-3 red is advanced by the following procedure.

(I) The diffraction angle of the first dispersive crystal 2 is set to an angle Θ ₁ close to 45 degrees (π / 4red). Move the gantry 10 to move the first dispersive crystal 1
The rotation center of the second dispersive crystal 3 is located on the X-ray axis of the diffracted X-ray. After that, the diffraction angle θ ₂ of the second dispersive crystal 3
The tilt angle ₂ is adjusted so that the X-ray diffracted by the second dispersive crystal 3 enters the X-ray detector 4. Then
₂ is It will be set to.

(II) The diffraction angle of the first dispersive crystal ₂ is set to the lowest angle Θ ₂ in the usable range. Move the gantry 10 to move the first dispersive crystal 2
The rotation center of the second dispersive crystal 3 is located on the X-ray axis of the diffracted X-ray. After this, the diffraction angle θ ₂ of the second dispersive crystal 3
The tilt angle ₁ of the first dispersive crystal 2 is adjusted so that the X-ray diffracted by the second dispersive crystal 3 enters the X-ray detector 4. Then, the tilt angle ₁ of the first dispersive crystal is It will be set to.

FIG. 5 is a flow chart showing these adjustments (I) and (II).

In this example, l = 190 mm, L = 2,500 mm Θ ₁ = 45 degrees, Θ
₂ = 10 degrees and the since the operation (I) and (II) a tilt angle ₂ of the first analyzing crystal 3 of tilt angle ₁ and the second analyzing crystal 4 each performed once decreased both by 9.1%. Therefore, if operations (I) and (II) are repeated 25 times, ₁ and ₂ will be about 1/10 of the initial setting value, and the accuracy required for practical use | ₁ |, |
₂ | <10 ^-3 red will be obtained.

According to the double crystal X-ray spectrometer of this embodiment, the tilt angle of the dispersive crystal can be adjusted without depending on experience.
This has the effect of shortening the time required to adjust the tilt angle of the double crystal X-ray spectrometer.

In addition, since the tilt angle can be adjusted to about 10 ^-3 rad, the setting error of the X-ray wavelength due to the misalignment of the tilt angle can be suppressed to a relative error of 10 ^-6. If it can be reduced, it will have an effect.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY The present invention makes it possible to easily adjust the tilt angle of the dispersive crystal and to provide a double crystal X-ray spectroscope with an automatic optical axis adjustment mechanism with high X-ray wavelength setting accuracy, which has a great industrial effect. It will be.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of a double crystal X-ray spectroscope of the present invention, FIG. 2 is an explanatory view schematically showing the principle of the double crystal X-ray spectroscope, and FIG. 3 is a tilt angle of the dispersive crystal. 4 is an explanatory view schematically showing the adjusting method of FIG. 4, FIG. 4 is an explanatory view of the configuration of the tilt angle adjusting means in FIG. 1, and FIG. 5 is a flow chart for adjusting the tilt angle of the dispersive crystal in the embodiment of FIG. is there. 1 ... X-ray source, 2 ... first dispersive crystal, 3 ... second dispersive crystal, 4 ... X-ray detector, 7,13 ... micrometer,
8,14 …… Diffraction angle setting motor, 9,15 …… Flying angle adjusting motor, 10 …… Mounting base, 11 …… Ball screw, 12 …… Mounting base moving motor, 18 …… Control device.

Claims (2)

[Claims] 1. A first flat-type dispersive crystal having a center of rotation on an X-ray beam emitted from an X-ray source and being parallel, and the first flat-type dispersive crystal.
The X-ray beam diffracted by the flat plate-type dispersive crystal is incident, and the diffracted X-ray is emitted from the X-ray source and emitted in a direction parallel to the incident X-ray beam, The second having the center of rotation on the X-ray beam diffracted by the crystal
In the two-crystal X-ray spectroscope having the flat-plate type dispersive crystal, the rotating means and the tilting means for setting the diffraction angles respectively provided in the first and second flat-plate dispersive crystals. A tilt angle adjusting means for adjusting an angle, a dispersive crystal spacing setting means for setting an interval between the first flat-plate type dispersive crystal and the second flat-plate dispersive crystal, and the second flat-plate dispersive crystal. Position-sensitive X-ray detector provided on the X-ray axis diffracted by and the rotation means of the first and second flat-plate type dispersive crystals using the detection result of the position-sensitive X-ray detector. And a means for controlling the tilt angle adjusting means and the spectroscopic crystal spacing setting means, and a double crystal X-ray spectrometer. 2. The double crystal X according to claim 1, wherein the second flat-plate type dispersive crystal is movable in a direction parallel to an incident X-ray beam emitted from the X-ray source and made parallel. Line spectrometer.