X-Ray converging mirror

Abstract: The present invention relates to an X-ray converging mirror (9) installed in the vicinity of an X-ray source (1) and reflecting X-ray beams emitted from the X-ray source (1) in the direction of the X-ray irradiating position. The cross-sectional profile of this mirror (9) is formed by a curve expressed by the following equation: x = ytan [1-ln (y/b)] wherein b denotes a point on the y-axis when dx/dy = 0.

Description: The present invention relates to an X-ray converging mirror located in the vicinity of the X-ray sources and for reflecting X-ray beams emitted from the X-ray sources in the X-ray irradiation position direction in the X-ray irradiation device such as X-ray analysis microscopes. In recent years, X-ray analysis microscopes have begun to be used in the analysis of biological tissues such as plants and small animals as well as minerals or in the field of various analysis and quality control of semiconductor packages and electronic parts. Now, in the X-ray analysis microscope, it is necessary to irradiate microscopic portion of specimens with fine X-ray beams which are important for analysis as a probe, but conventionally, fine X-ray beams are generated using a microfocus X-ray tube and at the same time, as an X-ray converging mirror for converging and focusing the fine X-ray beams at the X-ray irradiation position, for example, ellipsoid of revolution type reflecting mirrors as shown in Japanese Patent Publication No. Hei 4-6903, Hei 5-27840, and Hei 5-43080, etc. are used (cf. also EP-A-0 262 834). FIG. 3 schematically shows the ellipsoid of revolution type reflecting mirror, and in FIG. 3, numeral 31 is an X-ray source installed at the first focal point of the ellipsoid of revolution type reflecting mirror 30, and numeral 32 is a specimen installed at the second focal point of the mirror 30. Among the X-ray beams emitted from the X-ray source 31, those reflected on the reflecting surface of the mirror 30 are all converged to the specimen 32 surface. However, because X-ray beams impinging in the vicinity of the central portion of the mirror 30 as in the case of X-ray beams shown with numeral 33 have a small incidence angle α with respect to the reflecting surface tangent 34 when an ellipsoid of revolution type reflecting mirror 30 is used for an X-ray converging mirror, the reflectivity at the reflecting surface is high and the ratio of the X-ray impinging in the specimen 32 (X-ray efficiency) is high, but as in the case of the X-ray beams shown with numeral 35, because those impinging in the vicinity of the X-ray source 31 of the mirror 30 have a large incidence angle β with respect to the reflecting surface tangent 36, it has a problem in that the X-ray permeability at the reflection surface is high and the X-ray efficiency lowers. This invention has been made with the above-mentioned matter taken into account, and it is the main object of this invention to provide an X-ray converging mirror that can reflect X-ray beams satisfactorily in the X-ray irradiation position direction in the vicinity of the X-ray source. To solve this object, the present invention provides an X-ray converging mirror as specified in the claim. An X-ray converging mirror installed in the vicinity of an X-ray source and provided for reflecting X-ray beams emitted from the X-ray source in the X-ray irradiation position direction is characterized in that the cross-sectional profile of the mirror is a curve defined by the following expression: x=ytan[1-ln(y/b)] wherein  is set to the critical angle or less and b denotes a point on the y-axis when dx/dy = 0. In the X-ray converging mirror of the above configuration, the reflectivity of X-ray beams in the vicinity of the X-ray source becomes high and the X-ray intensity increases as much. Consequently, it is possible to obtain an X-ray converging mirror with an excellent X-ray efficiency. Further details, objects and advantages of the invention will be apparent from the following description when taken in conjunction with the drawings, wherein: Fig. 1 schematically shows a principal portion of the X-ray analysis microscope with the X-ray converging mirror according to this invention assembled; FIG. 2 is a diagram explaining the inner profile of the X-ray converging mirror; and FIG. 3 is a diagram explaining a conventional technique. Referring now to drawings, the embodiments of the X-ray converging mirror according to the invention will be described in detail. FIG. 1 shows the principal portion of the X-ray analysis microscope with the X-ray channel according to this invention assembled. In FIG. 1, numeral 1 is a microfocus X-ray tube as an X-ray source, which comprises a filament 4 generating electron 3 and an X-ray target 6 for generating desired X-ray beams 5 by allowing the electron 3 to collide against the target and is housed in a container 2 held to a specified high vacuum. Numeral 7 is an X-ray transmission window comprising beryllium that allows the X-ray beams 5 generated at the X-ray target 6 to pass to the X-ray channel 8 (later discussed) side. Numeral 8 is an X-ray channel that guides the X-ray beams emitted from the microfocus X-ray tube 1 to the X-ray irradiation position direction, and comprises the material with a small amount of zinc added to, for example, silica glass. The X-ray channel 8 comprises an X-ray converging mirror 9 in the vicinity of the microfocus X-ray tube 1 and an X-ray channel portion 10 on the X-ray irradiation position side connected thereto. The cross-sectional profile of the X-ray converging mirror 9 can be expressed by the equation of x = ytan  [1-ℓn (y/b)] (where, b is a point on the y-axis when dx/dy is 0.) The deducing process will be discussed later. The X-ray channel portion 10 is equipped with the profile similar to that on the second focal point side of the ellipsoid of revolution type reflecting mirror 30 and is joined to the open side of the X-ray converging mirror 9 expressed by the Eq. (I). Numeral 11 is an XY-axis scanning stage provided on the other end side of the X-ray channel 8, and this XY-axis scanning stage 11 is held in such a manner that the X-ray beam from the X-ray tube 1 side converges to the surface of the specimen 12 placed on this, and in this embodiment, it is arranged in such a manner that the surface coincides with the focal point position of the X-ray channel portion 10. Though not illustrated, a scintillation detector for detecting the X-ray permeating the semiconductor detector or specimen 12 for detecting fluorescent X-rays is installed in such a manner to command the XY-axis scanning stage 11. Referring now to FIG. 2, description is made on the internal profile of the X-ray converging mirror 9 installed in the vicinity of the microfocus X-ray tube 1. As shown in FIG. 2, on X and Y planes, let  denote the angle made by tangent 14 at point P (x, y) on curve 13 passing origin 0 and the line 15 connecting origin 0 and point P, and let  denote the angle made by tangent 14 and perpendicular 16 to the y-axis at point P. Then, we have (assuming tan, tan << 1) x = ytan + ytan Differentiate both sides of Eq. (1). This would result in: dx/dy = tan + tan + y • (1/cos 2 ) • d/dy And from the gradient of tangent 14, we have dx/dy = tan From Eq. (2) and Eq. (3), we obtain the equation as follows: tan = tan + tan + y • (1/cos 2 ) • d/dy Consequently, tan + y • (1/cos 2 )) • d/dy =0 ∴ d/cos 2  = -tan • dy/y Integrate both side of Eq. (5). This would result in: tan = -tan • ℓny + C And if dx/dy=0, that is, =0 and y=b, we have C = tan • ℓnb Consequently, Eq. (6) is reduced to the following equation. tan = -tans • ℓny + tan • ℓnb = -tan (ℓny - ℓnb) From Eq. (1) and Eq. (8), x = ytan [1-ℓn (y/b)] (where, b denotes a point on y-axis when dx/dy is 0.) The X-ray converging mirror 9 with a cross section given by Eq. ( I ) is arranged in such a manner that a microfocus X-ray tube 1 is located at the origin (position of reference symbol 0 in FIG. 2). In the X-ray analysis microscope of the above configuration, the X-ray beam 5 generated at the microfocus X-ray tube 1 becomes fine X-ray beam of high brightness with a diameter less than 10µm by passing the X-ray channel 8. This fine X-ray beam 5 is applied to a specimen 12 placed on the XY-axis scanning stage 11, and the fluorescent X-ray generated from it is detected by a semiconductor detector and the X-ray that penetrates the specimen 12 is detected by a scintillation detector simultaneously, respectively. And by returning signals of each detector into images using the XY axis scanning signals, it is possible to obtain a mapping image of surface elements by fluorescent X-ray and a mapping image of internal construction by penetrating X-rays. In this invention, because the cross-sectional profile of X-ray converging mirror 9 located in the vicinity of the microfocus X-ray channel 1 is a curve expressed by the ( I ), the reflectivity of X-ray beam 5 in the vicinity of the microfocus X-ray tube 1 becomes high, and the X-ray intensity increases as much. Consequently, the X-ray efficiency of the X-ray converging mirror 9 improves and the measuring accuracy of the X-ray analysis microscope improves. In addition, the X-ray converging mirror 9 is small as compared to the conventional X-ray converging mirror, and it is possible to make the X-ray analysis microscope compact. In the above-mentioned embodiment, an ellipsoid of revolution type reflecting mirror is used for the X-ray channel portion 10 joined to the X-ray converging mirror 9, but needless to say, it is allowed to adopt the mirror of a profile conventionally used such as a paraboloid of revolution, etc. The X-ray converging mirror 9 of this invention is naturally able to be applied to other X-ray irradiation equipment using X-ray tubes other than the X-ray analysis microscopes. As described above, because the X-ray converging mirror of this invention is a curve whose cross-sectional profile is expressed by the following equation, x = ytan [1-ℓn (y/b)] (where, b denotes a point on the y-axis when dx/dy is 0), it is possible to configure an X-ray irradiation equipment of high measuring accuracy with good X-ray efficiency and a compact optical system.

Claims: An X-ray converging mirror (9) installed in the vicinity of an X-ray source (1) and reflecting X-ray beams emitted from the X-ray source (1) in the direction of the X-ray irradiating position, characterized in that the cross-sectional profile of this mirror (9) is formed by a curve expressed by the following equation: x = ytan [1-ln (y/b)] wherein b denotes a point on the y-axis when dx/dy is 0.

Inventors: KASHIHARA KOZO, ONOGUCHI AKIRA, KASHIHARA, KOZO, ONOGUCHI, AKIRA
Applicants: HORIBA LTD, HORIBA, LTD.
Application year: 1998
Main classification: G21K1
IPC codes: G21K1