1. Technical Field
The invention relates to a nondestructive analysis method, a nondestructive analysis device, and a specific object by analyzed the method/device.
2. Background Art
With conventional transmission X-rays, the contrast of a resulting image depends on the magnitude of absorption of the X-rays by the object. Namely, if there is a region where the elements, structures, and densities of substances with high X-ray absorptance are dense, that portion exhibits a low transmittance and can be caught as a dark shadow in an image.
There is also a recently known method of capturing the state of refraction of X-rays dependent on the elements, structures, and densities of substances, not the absorption of X-rays. Monochromatic parallel X-rays have a wave front (X-rays are plane waves) which varies with a phase shift caused by the object. Since the phase shift is equivalent to the amount of change of the wave front form, detecting the phase shift corresponds to detecting the wave front form.
Here, a transmission-type or reflection-type analyzer crystal is used to determine the wave front form. A bend of the wave front of X-rays may be considered as the X-rays being refracted to a different direction of propagation. The propagation direction varies slightly according to the gradient of the wave front.
Considering the situation where an angle of incidence is set so that the transmission-type or reflection-type analyzer crystal satisfies a diffraction condition with respect to the monochromatic parallel X-rays, the transmission-type or reflection-type analyzer crystal's function is to detect a certain gradient part of the wave front. The refraction angle of the X-ray beam is known as a mode for examining the phase shift caused by the object, i.e., the refraction angle of the image, and a phase distribution is determined from the distribution of refraction angles obtained.
To take a specific example of a technology for analyzing the internal structure of an object nondestructively, there have already been various techniques proposed as ways of obtaining an image inside an object by using X-rays, including Japanese Patent No. 2694049.
Here, the object is irradiated with monochromatic X-rays (in reality, the monochromatic X-rays in use refer to X-rays having a distribution on the order of approximately one ten-thousandth in terms of the ratio Δλ/λ, where Δλ is the accompanying distribution of the wavelength λ of the monochromatic X-rays), X-rays from the object are introduced to an analyzer crystal (also referred to as crystal analysis plate, crystal analysis device, etc.), and a transmission beam and a diffraction beam emitted from the transmission-type analyzer crystal (technically, based on the case called Laue case) are used to obtain the image inside the object. This utilizes the fact that the analyzer crystal has an angular-analysis capability. The image obtained by the angular-analysis is paired with a similar image having different contrast between the transmission beam and diffraction beam (a reverse image of opposite signs; specifically, a white-and-black image if the other image is black-and-white).
Japanese Patent No. 2694049 describes monochromatic parallel X-rays used with the transmission-type analyzer crystal passing through an object without causing reaction with the object, and the monochromatic parallel X-rays and the refraction X-rays from the object are obtained as a transmission beam and a diffraction beam with mutual superimposition. In this case, an X-ray bright-field image is obtained.
Here, the X-ray bright-field image refers to an image in which signals from the object are superimposed on an illuminated background. In contrast, an X-ray dark-field image refers to an image which consists chiefly of signals from the object with no or a scarcely illuminated background. (Millions of stars in the sky may be taken as an illustration of an X-ray dark-field image.)
Among other examples is U.S. Pat. No. 5,850,425, in which an object is irradiated with monochromatic X-rays, and the refraction X-rays from the object are introduced to an analyzer crystal to utilize reflection X-rays through the Bragg reflection emitted from the analyzer crystal as the reflection-type analyzer crystal (technically, based on the case called the Bragg case). U.S. Pat. No. 5,850,425 describes the monochromatic parallel X-rays used with the reflection-type analyzer crystal passing through an object without causing interaction of the object, and the monochromatic parallel X-rays and the refraction X-rays from the object are reflected with mutual superimposition. This also results in an X-ray bright-field image.
Another technique has also been proposed in which an object is irradiated with monochromatic X-rays, and refraction X-rays from the object are introduced to a pair of reflection-type asymmetric analyzer crystals for double reflection, so that an image distorted by the first reflection is corrected into an undistorted one by the second reflection.
Nevertheless, these conventional nondestructive analysis methods have demonstrated the following problems.
That is, any of the foregoing nondestructive analysis techniques can only obtain poor-contrast, hard-to-recognize images due to the configuration that is chiefly intended to obtain an X-ray bright-field image, or an X-ray image or information on an object, in which the monochromatic X-rays in use pass through the object without causing reaction with the object, and the monochromatic X-rays are superimposed with the refraction X-rays and the like from the object, i.e. superimposed with X-rays affected by the intensity of the X-rays incident directly in the X-ray bright-field image. It has thus been impossible to obtain nothing other than poor-contrast, hard-to-recognize images.
Furthermore, none of the aforementioned describes a method for obtaining an X-ray dark-field image from the resulting X-ray bright-field image.
Moreover, the nondestructive analysis technique of Japanese Patent No. 2694049 has the problem that when the angular-analysis capability of the transmission-type analyzer crystal is utilized, the effect of the wavelength distribution of the monochromatic X-rays remains, or equivalently, an achromatic condition (condition for simultaneous diffraction in all the wavelengths including the accompanying wavelength distribution Δλ of the wavelength λ of the monochromatic X-rays) fails to be satisfied since no consideration is given to parallelization between the atomic lattice planes of the monochromator for generating the monochromatic X-rays and the atomic lattice planes of the analyzer crystal. Furthermore, there is the problem of requiring complicated operations for storing a white-and-black image and a black-and-white image with successive rotations of the transmission-type analyzer crystal and forming a high contrast image through a computer since no consideration is given to forming the transmission-type analyzer crystal of a certain thickness. It is thus impossible to obtain the desired image of the object at one time.
The invention of this application has been achieved in view of the foregoing. Thus, an object of the invention is to solve the problems of the conventional art and provide a new nondestructive analysis method and nondestructive analysis device, as well as a specific object analyzed by the nondestructive analysis method and device, which can realize a configuration chiefly intended to obtain an X-ray dark-field image in particular, or an X-ray image or object information by X-rays, unaffected by the intensities of the directly incident X-rays and the monochromatic X-rays in use, with an elimination or a reduction of an unnecessary illuminated background of X-rays, and can obtain a high-contrast image from inside an object at one time with ease.
Here, the X-ray dark-field image differs from the X-ray bright-field image in that the X-ray dark-field image is made of an object image alone with no or a fractionally scarcely illuminated background, being characterized in that the imaging is possible even with weak object signals alone.