JP2002286657A - X-ray absorption fine-structure analyzer and x-ray ct apparatus using k absorption-end finite difference method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously measure the spectrum of two kinds of elements. SOLUTION: The X-ray absorption fine-structure analyzer is composed of a single crystal 2 which spectrally diffracts X-rays so as to be made monochromatic, a support part for a sample 7 which transmits the monochromatic X-rays 23 and an X-ray detector 8 which detects the X-rays transmitted through the sample 7. The first crystal 2 which is situated first from the incident side of the X-rays is a single crystal which divides the X-rays into two optical paths by their diffraction and their transmission.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray absorption fine structure (X-ray absorption fine structure) that measures an absorption spectrum using an X-ray as a probe and analyzes a local structure around the element from a spectrum on an absorption edge peculiar to the element. -ray Absorption Fine Structure: X
AFS) White X-ray with high parallelism as analyzer and X-ray source
The present invention relates to an X-ray CT (computer tomography) apparatus which obtains monochromatic X-rays from a single crystal or the like (e.g., synchrotron radiation) and obtains a high-contrast image of a specific element by a K-absorption edge difference method.

[0002]

2. Description of the Related Art An X-ray absorption fine structure spectrum can be obtained by irradiating a sample with monochromatic X-rays whose energy is continuously changed and measuring the absorption intensity of the X-ray transmitted through the sample. Depending on the type of the element, the position of the absorption energy unique to the element called the absorption edge differs. By analyzing the spectrum of the vibration structure placed on the absorption edge, the local structure around the specific element in the sample can be found. In recent years, many synchrotron radiation facilities have been constructed,
White (continuous) X-rays having an intensity as high as 06 times can be obtained. The conventional device consists of a crystal that converts white X-rays into a single color, a detector that detects the X-rays incident on the sample, a sample, and an X-ray detector that transmits the sample. The spectrum of the next element was measured by rotating it to an angle near the absorption edge of the element to be measured next.

[0003]

However, when measuring the spectra of a plurality of elements, there has been a problem that the measurement time is required for the number of the elements. This hindered the measurement “on the spot” where the measurement was performed while heating the sample or the like. The use of synchrotron radiation light sources has been widely used at present, but it requires a fee, and it is necessary to measure data of elements constituting many samples in a short time as possible.

Accordingly, an object of the present invention is to enable simultaneous measurement of the spectra of two types of elements.

Another object of the present invention is to enable a CT image to be obtained simultaneously with the energy values of two X-rays before and after the K absorption edge. It is another object of the present invention to obtain a CT image even at another absorption edge.

[0006]

In order to achieve the above object, the invention according to claim 1 comprises a single crystal that separates X-rays into monochromatic light and a sample supporting portion that transmits monochromatic X-rays. ,
An X-ray detector for detecting X-rays transmitted through the sample
In the X-ray absorption fine structure analyzer, the first crystal located first from the X-ray incidence side is a single crystal that divides the X-ray into two optical paths by diffraction and transmission.
It is a line absorption fine structure analyzer. According to a second aspect of the present invention, there is provided the X-ray absorption fine structure analyzer according to the first aspect, further comprising a second crystal for diffracting the X-ray divided into two optical paths by the first crystal. X-ray absorption fine structure analyzer. The invention of claim 3 is based on
A single crystal that disperses X-rays into monochromatic light, a support portion of a sample that transmits monochromatic X-rays, a single crystal that disperses X-rays transmitted through the sample, and an X-ray that detects the separated X-rays In the X-ray absorption fine structure analyzer comprising a detector, the first crystal located first from the incident side of the X-ray is a single crystal that divides the X-ray into two optical paths by diffraction and transmission. Having a second crystal that diffracts each of the X-rays divided into two, and having a third crystal that transmits one of the X-rays diffracted by the second crystal and diffracts the other. This is a characteristic X-ray absorption fine structure analyzer. According to a fourth aspect of the present invention, there is provided the X-ray absorption fine structure analyzer according to the third aspect, wherein the X-rays emitted from the third crystal are incident on the sample through a common optical path. It is a microstructure analyzer. According to a fifth aspect of the present invention, in the X-ray absorption fine structure analyzer according to the third aspect, an X-ray detector for irradiating the sample on the optical path of the second crystal and the third crystal is provided. This is a characteristic X-ray absorption fine structure analyzer. According to a sixth aspect of the present invention, there is provided a single crystal for dispersing an X-ray to monochromatic light, a subject supporting portion, a mechanism for moving a subject position, a control device for controlling a moving mechanism, and an X-ray detector. A X-ray CT apparatus using a K-absorption edge difference method comprising a control device for collecting signals from the X-ray detector and controlling the position of the single crystal, and a software and hardware for CT image reconstruction. The first crystal located first from the incident side of the X-ray is a single crystal that divides the X-ray into two optical paths by diffraction and transmission. is there. According to a seventh aspect of the present invention, there is provided an X-ray CT apparatus using the K-absorption edge difference method according to the sixth aspect, further comprising a light-condensing element that condenses the X-ray divided into two by the first crystal. An X-ray CT apparatus using the K-absorption edge difference method characterized by having According to an eighth aspect of the present invention, there is provided an X-ray CT using the K absorption edge difference method according to the seventh aspect.
In the device, the wavelength of the X-ray diffracted by the first crystal is λ ₂ ,
The wavelength of the X-ray that passes through the first crystal and is collected by the light-collecting element is λ
An X-ray CT apparatus using a K-absorption edge difference method, where _{1 is} assumed to be λ ₂ > λ ₁ . Claim 9
The invention of claim 7 uses X-absorption edge difference method according to claim 7.
In the X-ray CT apparatus, an X-ray absorption filter is provided between an optical path of the X-ray transmitted through the first crystal and the light-collecting element. .

[0007]

Embodiments of the present invention will be described below with reference to the drawings.
This will be described with reference to FIG. FIG. 1 shows a first embodiment according to the present invention.
FIG. 1 is a diagram showing a configuration of an X-ray absorption fine structure analyzer of FIG. This
Here, the absorption edge spectra of the two elements are
X-ray wavelength λ ₁And λ_TwoMeasured by the area containing
Assume that

As shown in FIG. 1, a white X-ray 21 extracted from a radiation light source 1 is incident on a first crystal 2 which is a single crystal made of silicon or the like and having a thickness of 10 μm to 1 mm, and is diffracted ( In FIG. 1, it is divided into those that are subjected to the Bragg condition) and those that are transmitted. X-rays diffracted by the first crystal 2 is monochromatic X-ray 23 with a wavelength lambda _2. Then, the light is further diffracted by the second crystal 5, passes through the sample irradiation X-ray measurement detector 6, and enters the sample.

On the other hand, X-rays transmitted through the first crystal 2 is incident to the second crystals 3, diffracted wherein the monochromatic X-ray 22 with a wavelength lambda _1, a sample X-ray measuring detector 4 Sample 7 transmitted
Incident on. In order to change the energy of the monochromaticized X-rays, the first crystal 2 and the second crystals 3, 5 rotate, and the second crystals 3, 5 have their axes moved by a driving unit (not shown), The optical path of the X-ray which is shifted from the sample with the rotation is corrected so as to be incident on the sample. Similarly, the positions of the sample irradiation X-ray measurement detectors 4 and 6 are controlled on the X-ray optical path. The X-rays transmitted through the sample 7 are respectively incident on the X-ray absorption measurement detectors 8 and 9 (the intensity thereof is denoted by I), and the corresponding sample irradiation X-ray measurement detectors 4 and 6 (this by the ratio of the intensity of each the I _0), two regions including wavelengths lambda ₁ and lambda _2, respectively,
That is, the X-ray absorption spectra of two elements (μ = ln
(I ₀ / I) is measured.

However, in this configuration, the energy resolution of the X-ray monochromatized to the wavelength λ ₁ is lower than that of the X-ray of the wavelength λ ₂ using two spectral crystals. Therefore, it is easy to provide a single crystal for performing spectroscopy between the sample and the detector (a) for X-ray absorption measurement.

Furthermore, in the configuration of the first embodiment, the test
The acquisition of X-rays from the source is based on the wavelength λ ₁And λ_TwoArea containing
Will vary. Therefore, the structure of the device shown in FIG.
It is possible.

FIG. 2 is a view showing a configuration of an X-ray absorption fine structure analyzer according to a second embodiment of the present invention. Note that FIG.
In this case, since the process from the emission of the second crystal to the passage of the second crystal and passing through the detector for measurement of sample irradiation is the same as that of the first embodiment, the description is omitted here.

As shown in FIG. 2, the X-rays 23 in the region including the wavelength λ ₂ have a thickness of 10 μm
The light passes through the 1 mm third crystal 10 and enters the sample 7. The X-rays 22 in the region including the wavelength λ ₁ are diffracted by the third crystal 10 (see FIG. 2).
Then, the light is incident on the sample 7. Thereby, the energy resolution is improved. The axis of the third crystal 10 is also controlled by a driving unit (not shown) so that the X-ray diffracted by the second crystal 5 and the optical path overlap with the rotation of the second crystals 3 and 5. The X-rays transmitted through the sample 7 are separated by the fourth crystal 11 into X-rays in a region including the wavelength λ ₁ and X-rays in a region including the wavelength λ ₂ , and the two X-ray absorption measurement detectors 8 and 9 are used. Then, the X-ray intensities of the two regions are measured simultaneously. The wavelength of X-rays detected by the X-ray absorption measurement detector 9 is preferably shorter than the X-ray wavelength detected by the X-ray absorption measurement detector 8. This is because a higher energy (short wavelength) X-ray is absorbed by the fourth crystal 11 at a smaller rate. It is also easy to arrange two spectral crystals after the sample 7 and to extract X-rays of each wavelength by diffraction. Also in that case, the absorption spectrum is extracted by rotating the axis of the spectral crystal and the detector in conjunction with the energy of the X-ray.

By setting the thickness of the first crystal to 10 μm to 1 mm, X-rays can be divided into two optical paths of diffraction and transmission.

The thickness of the third crystal is 10 μm to 1 mm.
Thus, two optical paths of X-rays can be made into one optical path by diffraction and transmission.

In addition, since the X-ray detector for irradiating the sample is arranged on the optical path of the second crystal and the third crystal, the absorption intensity of each wavelength can be measured accurately.

In the figures of the present embodiment, the Bragg condition is used for diffraction, but it is also possible to separate X-rays of two wavelengths before entering the sample even under Laue conditions. The position where the detector for X-ray measurement of the sample irradiation of X-ray incident on the sample is
The optical path immediately before the incident side with respect to the sample is good, but in the case of the configuration as shown in FIG. 2, the optical path immediately before the sample has the intensity of X-rays including two kinds of wavelengths. An optical path between the second and third crystals is desirable.

The K-absorption edge difference method uses X-ray absorption of energy peculiar to an element called an absorption edge which differs depending on the type of element. In combination with the CT method, the distribution state of elements inside a test object and The concentration of the element can be observed as an image. In recent years, many synchrotron radiation facilities have been constructed as X-ray sources, and white (continuous) X-rays having an intensity 106 times as high as those in the laboratory can be obtained. In the conventional apparatus, in order to perform the K-absorption edge difference method, it is necessary to obtain a CT image with two energy values before and after the absorption edge. Image data had to be measured. Hitherto, as a method for simultaneously obtaining images before and after the absorption edge, a method as described in JP-A-5-340893 has been proposed, but a large area is required for the first crystal. Also, as described in JP-A-5-340894,
In order to diffract X-rays having an energy width before and after the absorption edge by the first crystal, it was necessary to perform a special process of roughening the crystal surface. Japanese Patent Application Laid-Open No. HEI 5-5-267 discloses a method in which a minute divergent X-ray source is formed using X-ray focusing and reduction optical means, and X-ray CT is performed using divergent X-rays from this X-ray source.
No. 60702 is known, but here, no attempt has been made to simultaneously measure CT images before and after the absorption edge.

Therefore, an object of the following embodiment is to enable a CT image to be obtained with two X-ray energy values before and after the K absorption edge at the same time. It is another object of the present invention to obtain a CT image even at another absorption edge.

FIG. 3 is a diagram showing a configuration of an X-ray CT apparatus using a K-absorption edge difference method according to a third embodiment of the present invention.
Here, the energy value of the X-rays in the absorption edge before and after a certain element E2 and E1, it is assumed that the wavelength of X-rays corresponding thereto are each lambda ₂ and lambda _1. When this wavelength is determined, the angle of the first crystal 2 and the conditions of light collection by the light-collecting elements 32 and 34 (in FIG. 3, the angle of the reflection mirror which is the X-ray light-collecting element)
Are determined, these values are calculated by a computer or the like not shown in the figure, and the axis of each element is rotated based on the calculated values. Also, in consideration of the size of the sample 36 and the size of the image projected on the X-ray detectors 37 and 38,
The distance between the first crystal 2 and the X-ray condensing elements 35 and 34, the position of the sample 36, and the positions of the X-ray detectors 37 and 38 are calculated, and driven so that they are appropriately arranged. The high-brightness, high-parallelness white X-ray 21 extracted from the synchrotron radiation light source 1 has a thickness of 10 μm to 1 m made of silicon or the like.
The incident light is incident on the first crystal 2, which is a single crystal of m, and is divided into those that are diffracted (Bragg condition in FIG. 3) and those that are transmitted. X-rays diffracted by the first crystal 2 is monochromatic X-ray 23 with a wavelength lambda _2. Then, the X-rays incident on the X-ray condensing elements 32 and 34 are condensed, pass through the slits 33 and 35 provided at the converging point, and irradiate the sample 36 as divergent light. Since the position where light is collected changes depending on the wavelength of X-rays,
An operation for taking this into account is performed, and the X-ray focusing element 3
The positions of the slits 2 and 34 and the slits 33 and 35 are set by a drive system (not shown). The X-ray transmitted through the sample 36 is projected on the X-ray detectors 37 and 38 as an enlarged image. Examples of the X-ray detectors 37 and 38 include a photodiode array, a CCD, and an element typified by a position reading microchannel plate. Sample 36
The sample stage that supports is rotated by a pulse motor, and data is acquired from the X-ray detectors 37 and 38 at each angular step.
These data are stored in a storage device such as a memory, and these data are subjected to a necessary mathematical operation of a known mathematical conversion for converting a projection image into a cross-sectional image, thereby obtaining a CT image of the sample 36. For example, conversion is performed using a well-known method of converting a projected image at each angle into a cross-sectional image, for example, a Fourier transform method, a convolution method, or the like. At this time, the X-ray detector 37 obtains a CT image containing the X-ray of the wavelength λ ₁ after the absorption edge, and the X-ray detector 38 obtains a CT image of the wavelength λ ₂ before the absorption edge. By performing image processing, an image showing the distribution and concentration of the specific element can be obtained. In this optical system, the optical path between the first crystal 2 and X-ray focusing device 32, putting the X-ray absorbing filter 31, blocking is carried out X-ray having a wavelength shorter than the wavelength lambda ₁ .

FIG. 4 shows K absorption of a fourth embodiment according to the present invention.
It is a figure showing the composition of the X-ray CT device using the edge difference method.
X-rays are transmitted and diffracted through the first crystal 2 and split into two optical paths.
Until this is the same as in the third embodiment, it is described here.
Is omitted. As shown in FIG.
Wavelength λ diffracted by 4,3_TwoAnd λ ₁A monochromatic X-ray
You. The rotation axis of the second crystals 4 and 3 is based on the wavelength of the X-ray used.
Each λ_TwoAnd λ₁If you set
Computed by a computer, etc.
It is set to a sharp angle. Also, the first crystal 2 and the X-ray focusing element
Distance between the probes 41 and 43, the position of the sample 36 and the X-ray detector
The positions of the samples 37 and 38 are also the same as those of the third embodiment.
Considering the size and the projection magnification to the X-ray detectors 37 and 38
Thus, it is set by a drive system not shown in the figure. This
In the configuration of the above, the light was transmitted through the first crystal 2 by the second crystal 3
X-rays are also monochromatic. This wavelength λ₁Of monochromatic X-ray
Energy resolution is wavelength λ using two spectral crystals._Two
Lower than the X-ray of
I have.

As shown in FIG. 5, the absorption edge of an element rises at a certain energy value specific to the element, and the absorption intensity gradually decreases as the energy increases, and this characteristic further decreases. It is on the background. Therefore, since the absorption spectrum has a tail after the absorption edge rises, energy resolution is not required more than before the absorption edge. The X-ray of wavelength λ ₂ is monochromatic by two single crystals, and the X-ray of wavelength λ ₁ is monochromatic by one single crystal. Alternatively, since the optical system composed of apertures is also monochromatic, we used other absorption edges that do not have a sharp rise such as K absorption, and differences in the absorption edge structure caused by differences in the electronic state of the same element. CT
Images are also measured under certain conditions.

As shown in FIG. 4, X-rays diffracted by the second crystals 3 and 4 are condensed by X-ray condensing elements 41 and 43. A phase modulation type zone plate can be used as the light condensing element. In a zone plate using a transparent and opaque ring, a phase modulation type zone plate that condenses light using a transparent and semi-transparent ring is desirable because a ring-shaped intensity unevenness occurs in diffused light. Aperture 4 at focusing position
2,44 are installed. This aperture 42, 4
4 is driven variably. By reducing the hole diameter, the light becomes divergent from a minute light source, so that the spatial resolution of the projected image is increased. Further, similarly to the above, since the focused position changes depending on the wavelength of the X-ray, an operation taking this into consideration is performed, and the distance between the X-ray focusing elements 41 and 43 and the apertures 42 and 44 varies depending on the drive system. I do.

The X-ray diverging from the slit spreads in a cone and irradiates the sample, and is obtained as a two-dimensional projected image by the detector. As in the third embodiment, after this image is recorded, arithmetic processing is performed to obtain a three-dimensional CT image before and after the absorption edge at a time. Thereafter, by performing arithmetic processing of both images, an image showing the three-dimensional distribution and concentration of the specific element can be obtained.

Further, by providing a drive system for appropriately moving the position of the subject on the optical path of the X-ray emitted from the two light-collecting elements, the wavelength of the X-ray and an arbitrary projection magnification can be selected.

The thickness of the first crystal is 10 μm to 1 mm
In the energy region where the K absorption edge of the main element exists, X-rays can be separated by diffraction and transmission.

Also, a slit or aperture is provided on the emission side of the light-collecting element, and a driving system for changing the arrangement of the slit or aperture and the light-collecting element is provided. And irradiating X-rays diverging from the focusing position can be obtained.

In addition, by using a crystal and a phase-type Fresnel zone plate as the light condensing element, it is possible to converge, bend the X-ray optical path in the direction of the sample, and monochromatic X-rays.

Further, by providing a mechanism in which the slit interval or the diameter of the aperture hole is made variable, an X-ray irradiation system that diverges from a smaller point can be created, and the projected image measured by the detector can be obtained. Spatial resolution can be increased.

In the figures of the present embodiment, the Bragg condition is used for the diffraction of the crystal element. However, even under the Laue condition, an optical system that divides into two X-rays before entering the sample is possible. In the third and fourth embodiments, the light condensing means having the two functions of changing the optical path and condensing light is constituted by an X-ray reflection mirror in the third embodiment, and in the fourth example, a crystal and a zone are used. And a plate.

The present invention is not limited to the above embodiment. That is, various modifications can be made without departing from the gist of the present invention.

[0032]

As described above, according to the first aspect of the present invention, the X-ray is divided into two optical paths by diffraction and transmission by the first crystal located first from the X-ray incident side. X-rays can be divided into X-rays having a monochromatic wavelength and continuous X-rays other than the wavelength. According to the second aspect of the present invention, each of the X-rays divided into two by the first crystal is made incident on two second crystals for diffracting, thereby obtaining two types of monochromatic wavelengths to be extracted. You can get a line. According to the third aspect of the present invention, by having a third crystal that transmits one of the X-rays reflected by the two second crystals and diffracts the other X-ray, two types of energy resolutions that are substantially equal are provided. X-rays having a monochromatic wavelength can be incident on the sample. According to the fourth aspect of the present invention, the X-rays emitted from the third crystal are made incident on the sample in one optical path, whereby the absorption spectrum at the same position on the sample can be measured. Further, according to the fifth aspect of the invention, by using the X-ray reflection mirror as the light-collecting element of the second aspect, it is possible to collect light and bend the X-ray optical path toward the sample at a time. According to the sixth aspect of the present invention, the X-ray is divided into two optical paths by diffraction and transmission in the first crystal positioned first from the X-ray incidence side, thereby irradiating the sample with two systems. A system can be formed. According to the seventh aspect of the present invention, the sample is irradiated with X-rays diverging from the light-converging point by having two light-condensing elements that respectively condense the X-rays divided into two by the first crystal. Thus, an enlarged projected image can be obtained. According to the invention of claim 8, according to claim 6,
Assuming that the wavelength of the X-ray diffracted in the first crystal is λ ₂ , and the wavelength of the X-ray condensed in the condensing element of claim 2 is λ ₁ , by satisfying λ ₂ > λ ₁ ,
The energy resolution of X-rays of wavelength λ ₂ is improved, and data suitable for the shape of the absorption intensity at the absorption edge can be obtained. According to the ninth aspect of the present invention, an X-ray absorption filter is provided between the optical path of the X-ray transmitted through the first crystal of the sixth aspect and the light-collecting element of the second aspect. It is possible to remove X-rays having a wavelength that becomes a noise upon incidence.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an X-ray absorption fine structure analyzer according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an X-ray absorption fine structure analyzer according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of an X-ray CT apparatus using a K-absorption edge difference method according to a third embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of an X-ray CT apparatus using a K-absorption edge difference method according to a fourth embodiment of the present invention.

FIG. 5 is a diagram showing an X-ray absorption spectrum.

[Explanation of symbols]

Reference Signs List 1 light source (emitted light) 2 first crystal 3 second crystal 4 sample irradiation X-ray measurement detector 5 second crystal 6 sample irradiation X-ray measurement detector 7 sample 8 X-ray absorption measurement detector 9 X-ray absorption Detector for measurement 10 Third crystal 11 Fourth crystal 21 White X-ray 22 X-ray with wavelength λ ₁ 23 X-ray with wavelength λ ₂ 31 X-ray absorption filter 32 X-ray condenser 33 Slit 34 X-ray condenser 35 Slit 36 Sample (subject) 37 X-ray detector 38 X-ray detector 41 X-ray condenser 42 aperture 43 X-ray condenser 44 aperture

Claims (9)

[Claims] 1. An X-ray crystal comprising: a single crystal that separates X-rays into monochromatic light, a sample supporting portion that transmits monochromatic X-rays, and an X-ray detector that detects X-rays transmitted through the sample. In the X-ray absorption fine structure analyzer, the first crystal located first from the X-ray incidence side is a single crystal that divides the X-ray into two optical paths by diffraction and transmission. Structural analyzer. 2. The X-ray absorption fine structure analyzer according to claim 1, further comprising a second crystal for diffracting the X-ray divided into two optical paths by the first crystal. Absorption fine structure analyzer. 3. A single crystal that separates X-rays into monochromatic light, a supporting portion of a sample that transmits monochromatic X-rays, a single crystal that separates X-rays transmitted through the sample, and a spectroscopic X-ray. In the X-ray absorption fine structure analyzer comprising an X-ray detector for detecting X-rays, the first crystal located first from the X-ray incident side is:
A single crystal that divides an X-ray into two optical paths by diffraction and transmission, has a second crystal that diffracts each of the X-rays divided into two by a first crystal, and is each diffracted by a second crystal. An X-ray absorption fine structure analyzer comprising a third crystal that transmits one of the X-rays and diffracts the other. 4. The X-ray absorption fine structure analyzer according to claim 3, wherein the X-rays emitted from the third crystal are incident on the sample through a common optical path. . 5. The X-ray absorption fine structure analyzer according to claim 3, wherein an X-ray detector for irradiating the sample is arranged on the optical path of the second crystal and the third crystal. X-ray absorption fine structure analyzer. 6. A single crystal that separates X-rays into monochromatic light by dispersing the X-rays, a subject supporting portion, a mechanism for moving a subject position, a control device for controlling a moving mechanism, an X-ray detector, and an X-ray detector. A controller for collecting detector signals and controlling the position of the single crystal;
In an X-ray CT apparatus using a K-absorption edge difference method composed of software and hardware for T image reconstruction, a first crystal located first from the incident side of X-rays converts X-rays by diffraction and transmission. An X-ray CT apparatus using a K-absorption edge difference method, which is a single crystal split into two optical paths. 7. The X-ray CT apparatus using the K-absorption edge difference method according to claim 6, further comprising a light-condensing element that condenses each of the X-rays divided into two by the first crystal. An X-ray CT apparatus using the K-edge difference method. 8. An X-ray CT apparatus using the K-edge difference method according to claim 7, wherein the wavelength of the X-ray diffracted by the first crystal is λ ₂ , An X-ray CT apparatus using the K-absorption edge difference method, wherein λ ₂ > λ ₁ where λ ₁ is the wavelength of the focused X-ray. 9. An X-ray CT apparatus according to claim 7, wherein an X-ray absorption filter is provided between an optical path of the X-ray transmitted through the first crystal and the light-collecting element. An X-ray CT apparatus using the K-absorption edge difference method.