JPH11258400A - Target for transition radiation x-ray generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a target for an X-ray generator that is easily fabricated and makes it possible to obtain X rays with intensity and good monochromatism. SOLUTION: A target has a structure where thin films 2, 4, 6, 8 and 10 made of substances that are highly efficient in transition radiation and those 3, 5, 7 and 9 made of substances that are high in the transmissivity of X rays are laminated alternately on a substrate 1. The thickness of the thin films 2, 4, 6, 8 and 10 made of the radioactive substances and the thin films 3, 5, 7 and 9 made of interstitial substances is set at the value where transitional radiation X rays with desired energy satisfy an interference condition. By filling with the space between the thin films made of the radioactive substances with the thin films made of interstitial substances, the former films are accurately arranged at equal intervals and interference is given to the transitional radiation X rays.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a target structure for an X-ray generator that generates transition radiation X-rays by irradiating an electron beam.

[0002]

2. Description of the Related Art Conventionally, as a target for an X-ray generator for generating transition radiation X-rays by electron beam irradiation, a multilayer thin film in which thin films made of a substance having high transition radiation generation efficiency are arranged at regular intervals. Target is known. FIG. 4 (a)
FIG. 4 is a plan view of a conventional target for a transition radiation X-ray generator, and FIG.
4B is a sectional view taken along line AA of FIG. 4A, and FIG. 4C is a plan view of a spacer described later. A conventional transition radiation target has a structure in which thin films 12, 14, 16, 18, and 20 made of a substance (radiation material) having high transition radiation generation efficiency are arranged at equal intervals, and a vacuum is applied between the thin films. Or it was a gap such as the atmosphere. Such targets are thin films 12,
A spacer 13 as shown in FIG. 4 (c) in which holes for providing the above gaps with the spacers 14, 16, 18, 20 are arranged at the center.
It is manufactured by mechanically laminating 15, 17, and 19 alternately.

[0003]

The thickness of the thin film used for the transition radiation target is usually about 0.1 to 10 μm, and the distance between the thin films, that is, the thickness of the spacer is also about the same.
Such a target in which very thin films are stacked at a small interval has a problem that it is difficult to manufacture. The reason is,
This is because, since the distance between the thin films is very small, the thin films are often deformed during the manufacturing process and come into contact with each other even if a spacer is present, and in severe cases, the thin films themselves are damaged. Further, X-rays obtained when such a target is irradiated with an electron beam have low intensity and poor monochromaticity (uniformity of wavelength). The reason is that if the variation in the thin film interval greatly exceeds the allowable error of several percent, the coherence of transition radiation X-rays emitted from each thin film is lost. In general, it is preferable that these targets be irradiated with an electron beam in a vacuum in order to prevent scattering of the electron beam and attenuation of generated X-rays, but it cannot be used in a vacuum with a conventional structure. There was a problem. The reason is that since air exists in the gap between the thin films, a large pressure is applied between the air layer and the vacuum in a vacuum, and the thin film is damaged.
The present invention has been made to solve the above problems,
An object of the present invention is to provide a target for a transition radiation type X-ray generator that can be easily manufactured, and that can obtain strong and good monochromatic transition radiation X-rays.

[0004]

SUMMARY OF THE INVENTION According to the present invention, there is provided an X-ray generator for generating transition radiation X-rays by irradiating an electron beam. A first thin film formed of a substance having a high X-ray transmittance, wherein the first thin film is filled with a second thin film made of a substance having a high X-ray transmittance; The thickness of the thin film is set to a value such that transition radiation X-rays of desired energy satisfy the interference condition. As described above, by filling the gap between the first thin films with the second thin film having a predetermined thickness made of a substance having a high X-ray transmittance, the first thin film made of a substance having a high transition radiation generation efficiency can be precisely formed. The transition radiation X-rays emitted from the first thin film can be given sufficient coherence. In the present invention, the first and second thin films are formed on a thin substrate made of a material having low X-ray generation efficiency.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] Next, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view of a target for a transition radiation X-ray generator according to a first embodiment of the present invention. The target of this embodiment is a thin film 2 made of a substance having a high transition radiation generation efficiency (hereinafter referred to as a radiation substance) on a substrate (membrane) 1.
4, 6, 8, 10 and substances having high X-ray transmittance (hereinafter, referred to as
This is a structure in which thin films 3, 5, 7, and 9 made of interstitial materials are alternately stacked.

[0006] X-rays generated from the substrate 1 at the time of electron beam irradiation disturb the interference effect of transition radiation X-rays generated from the thin films 2, 4, 6, 8 and 10. However, the substrate 1 is made of a material having a low electron density such as SiN or the like, that is, a material having a low generation efficiency of transition radiation or bremsstrahlung X-rays, and the influence of the generated X-rays is reduced.
If is sufficiently thin, the effect can be almost ignored. By using this substrate 1, the thin films 2, 4, 6,
The physical intensity of the target can be increased without affecting the transition radiation X-rays generated from 8,10.

[0007] The radiating substance is preferably a simple substance or a compound of a medium heavy metal element having a high transition radiation generation efficiency, that is, a solid substance having a high electron density, and a material having no absorption edge around the generated X-ray wavelength. . As an example of a material that satisfies such conditions, nickel is promising in the case of targeting an X-ray region of 1 to 10 keV. As the interstitial material, a solid material having the highest possible X-ray transmittance, that is, the lowest possible electron density is preferable. For example,
Simple elements of light elements such as beryllium, carbon, and nitrogen or compounds thereof are preferable.

The thicknesses of the radiating material thin films 2, 4, 6, 8, and 10 and the interstitial material thin films 3, 5, 7, and 9 are set to values such that transition radiation X-rays of desired energy satisfy interference conditions. You. At this time, the above-mentioned interference condition is set to the radiation substance thin films 2, 4,
6, 8, 10 intervals, ie, interstitial material thin films 3, 5,
The energy of the transition radiation X-ray is determined by the film thickness of the radiation material thin films 2, 4, 6, 8, and 10, and the interval between them.

The above configuration is realized by alternately forming a radiating substance and an interstitial substance on the substrate 1 by an appropriate thin film forming method. As a method for forming a thin film, a vapor deposition method, a CV
D method, sputtering method, MBE method and the like can be used. Note that the number of layers of the thin film may be arbitrarily determined, but care must be taken since excessively increasing the number of layers absorbs transition radiation X-rays generated from the radiating substance.

FIG. 2 is a diagram showing energy spectra of transition radiation X-rays obtained by the target of the present embodiment and the conventional target. In FIG. 2, E1 is the energy spectrum of the transition radiation X-ray by the target of the present embodiment, and E2 is the energy spectrum of the transition radiation X-ray by the conventional target. As a target of the present embodiment, 0.
A 188 μm-thick nickel thin film and a 0.22 μm-thick carbon thin film were alternately deposited on each of 10 layers, and a conventional target was a 0.188 μm-thick nickel thin film deposited at 10 unequal intervals. (The thickness of the spacer between the nickel thin films is unequal).

FIG. 2 shows an X-ray spectrum obtained by irradiating these targets with electrons having an energy of 15 MeV and observing transition emission X-rays generated at this time at an angle of 34 mrad with respect to the traveling direction of the electron beam. Is shown. In a conventional target, the coherence of transition radiation X-rays is lost due to a large variation in the distance between the radioactive substance thin films. Therefore, as shown by E2 in FIG. 2, the X-ray obtained when a conventional target is irradiated with an electron beam has low intensity and poor monochromaticity. On the other hand, according to the target of the present embodiment, since sufficient coherence of transition radiation X-rays can be obtained, X-rays having strong and good monochromaticity can be obtained as shown by E1 in FIG. I understand.

[Embodiment 2] FIG. 3 is a sectional view of a target for a transition radiation type X-ray generator according to a second embodiment of the present invention. Is attached. The target of the present embodiment has a structure without the substrate 1 as compared with the target of the first embodiment. Such a structure can be realized by removing the target substrate 1 of FIG. 1 by various etching methods conventionally used in a semiconductor process or the like. Thus, the influence of the substrate 1 can be completely removed.

[0013]

According to the present invention, as described in claim 1, by filling the space between the first thin films with the second thin film, the first thin film made of a substance having high transition radiation generation efficiency can be formed. Since they can be arranged at equal intervals with high accuracy, it is possible to give sufficient coherence to the transition radiation X-rays emitted from the first thin film, and to obtain transition radiation X-rays that are strong and have good monochromaticity. . In addition, since the well-known thin film forming method can be used for forming the first and second thin films, the manufacturing can be facilitated and the mechanical manufacturing portion can be eliminated, thereby preventing the thin film from being damaged in the manufacturing process. be able to. Furthermore, since there is no air layer between the first thin films, it can be used even in a vacuum.

Further, the physical strength of the target can be increased by forming the first and second thin films on a thin substrate made of a material having a low X-ray generation efficiency. it can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a target for a transition radiation X-ray generator according to a first embodiment of the present invention.

FIG. 2 is a diagram showing energy spectra of transition radiation X-rays obtained by the target of FIG. 1 and a conventional target.

FIG. 3 is a cross-sectional view of a target for a transition radiation X-ray generator according to a second embodiment of the present invention.

FIG. 4 is a plan view and a sectional view of a conventional target for a transition radiation X-ray generator, and a plan view of a spacer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2, 4, 6, 8, 10 ... Radiation material thin film 3,
5, 7, 9 ... interstitial material thin film.

Claims (2)

[Claims] 1. A multi-layer thin film target for a X-ray generator for generating transition radiation X-rays by electron beam irradiation, wherein first thin films made of a substance having high transition radiation generation efficiency are arranged at regular intervals. A second film made of a substance having a high X-ray transmittance between the first thin films.
Wherein the thickness of the first and second thin films is set to a value such that transition radiation X-rays of desired energy satisfy interference conditions. For target. 2. The target for a transition radiation X-ray generator according to claim 1, wherein the first and second thin films are formed on a thin substrate made of a material having a low X-ray generation efficiency. A target for a transition radiation type X-ray generator.