JP3729896B2 - Rotating anode X-ray tube - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rotary anode type X-ray tube, and more particularly to an improvement in the shape of the disk-like anode target.
[0002]
[Prior art]
In a conventionally known rotary anode X-ray tube, as shown in FIGS. 4 and 5, a disk-like rotary anode target 11 is fixed to a cylindrical rotary body 13 via a shaft 12. The rotating body 13 is rotatably supported by the fixed body 15 via a bearing 14. A cathode 16 is disposed facing the anode target 11, and an electron beam e indicated by a dotted line is emitted from the filament cathode 17. A vacuum vessel 18 is provided so as to accommodate these anode target and cathode. In this vacuum vessel 18, a portion surrounding the anode target and the cathode is constituted by a metal vessel 18 a, and glass vessels 18 b (only one is shown) are joined to both ends thereof. An X-ray emission window 19 is hermetically joined at a predetermined position of the metal container 18a, that is, at a position facing the focal point F where the electron beam e on the anode target surface collides to generate X-rays.
[0003]
In operation, X-rays generated from the focal point F on the anode target surface that rotates at high speed are extracted and used in a direction substantially perpendicular to the tube axis through the radiation window 19. Note that an X-ray beam path used for purposes such as X-ray imaging is represented by a symbol X, and its central axis is represented by a symbol Xa. The anode target 11 is formed with a focal track surface 11f that apparently corresponds to the focal point F.
[0004]
[Problems to be solved by the invention]
By the way, some of the electrons that collided with the anode target surface are reflected by the target surface and draw a trajectory like symbol Re to reach the target surface again. For this reason, collisions of reflected electrons having a relatively high density occur around the focal point F, and undesired out-of-focus X-rays are generated. The out-of-focus X-ray generation region is schematically represented by the symbol Rf in FIG.
[0005]
Needless to say, if a lot of such out-of-focus X-rays are generated and mixed in the intended X-ray beam path, for example, the resolution of the X-ray image is deteriorated. As in the case of an X-ray CT scanner, the higher the electron beam acceleration voltage and current density of the X-ray tube, the more this generation of out-of-focus X-rays can be ignored.
[0006]
It is an object of the present invention to provide a rotating anode type X-ray tube that eliminates the above-mentioned inconveniences and can reduce the mixing of out-of-focus X-rays into the intended X-ray beam path with a relatively simple structure. And
[0007]
[Means for Solving the Problems]
In the present invention, recesses that cannot be seen from the central axis in the X-ray beam extraction direction are formed in at least an inner region and an outer region that are close to the X-ray focal track surface of the anode target, and the recesses in the outer region are outer peripheral edges. It is a rotating anode type X-ray tube which is gradually shallowly recessed toward .
[0008]
According to the present invention, the out-of-focus X-rays generated by the electrons reflected from the focal region on the anode target surface and reaching the adjacent recesses are blocked by the anode target itself, and are not passed to the intended X-ray beam path. Do not mix. Therefore, the out-of-focus X-ray emission is effectively reduced.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment will be described below with reference to the drawings. The same parts are denoted by the same reference numerals. In the embodiment shown in FIGS. 1 and 2, the inner peripheral recess 11m and the outer peripheral recess 11n are formed by removing the inner region and the immediate outer region of the focal track surface 11f of the anode target 11 in a tapered shape by cutting. is there.
[0010]
The center axis Xa of the intended X-ray beam path X is perpendicular to the rotation axis Z of the anode target in this embodiment, and the spread angle Qa with respect to the center axis Xa of the X-ray beam path X is about 16 degrees. is there. Further, the inclination angle Qb of the focal track surface 11f of the anode target with respect to the central axis Xa of the X-ray beam path is approximately 16 degrees.
[0011]
Therefore, the tapered inner peripheral recess 11m adjacent to the inner peripheral edge of the focal track surface 11f is at an angle Qm of about 18 degrees with respect to the central axis Xa of the X-ray beam path and from above the central axis Xa of the X-ray beam path. It is gradually recessed toward the shaft 12 so that it cannot be seen. Further, the outer peripheral recess 11n adjacent to the outer peripheral edge of the focal track surface 11f is cut off from the region where the electron beam e collides along the traveling direction of the electron beam and cannot be seen from above the central axis Xa of the X-ray beam path. Thus, the taper is gradually recessed shallowly toward the outer peripheral edge of the target. The outer peripheral recess 11n is formed at an angle Qn of approximately 18 degrees with respect to the central axis Xa of the X-ray beam path.
[0012]
According to this embodiment, even if electrons reflected from the focal track surface reach the concave portions on the inner peripheral side and the outer peripheral side of the focal track surface and generate out-of-focus X-rays, It is blocked by itself and is not radiated in the direction of the intended X-ray beam path X. Therefore, the out-of-focus X-ray emission can be substantially reduced.
[0013]
In the above embodiment, the bottom surfaces of the inner recess 11m and the outer recess 11n are recessed so that they cannot be seen from the center axis Xa of the X-ray beam path. The bottom surface of each concave portion cannot be seen from anywhere in the range of the X-ray beam path X.
[0014]
In the embodiment shown in FIG. 3, the outer peripheral recess 11n is formed by notching a relatively long target region along the tube axis direction from the outer peripheral edge of the focal track surface 11f. The upper surface 16a of the focusing electrode of the cathode 16 and the upper surface of the filament cathode 17 are opened at an angle Qk of about 5 degrees so as to open outward with respect to the surface H perpendicular to the rotation axis Z and the center axis Xa of the X-ray beam path. It is tilted and fixed.
Thereby, the electron beam e emitted from the cathode travels slightly away from the rotation axis Z and enters the focal track surface 11f of the anode target. Therefore, a relatively large amount of electrons reflected by the focal track surface 11f are reflected and returned to the outside. Since the outer periphery from the outer peripheral edge of the focal track surface is a notched recess, the out-of-focus X-ray generated from the recess is not emitted in the direction of the intended X-ray beam path X.
[0015]
In the above embodiment, the concave portion is formed by notching the outer side of the focal track surface so as to have a step. However, the present invention is not limited to this, and the outer peripheral edge of the focal track surface is configured to coincide with the outer peripheral edge of the anode target. May be.
[0016]
In addition, the vacuum vessel is not limited to the portion surrounding the anode target and the cathode made of a metal vessel, and the present invention can be applied to a case where almost the whole is made of an insulator such as glass or ceramics. . Furthermore, the present invention is also suitable for the anode target having a base portion made of graphite.
[0017]
【The invention's effect】
As described above, according to the present invention, mixing of out-of-focus X-rays into the X-ray beam path intended for use can be reduced with a relatively simple structure.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an essential part showing an embodiment of the present invention.
FIG. 2 is an enlarged half sectional view of the main part of FIG.
FIG. 3 is an enlarged half sectional view of a main part showing another embodiment of the present invention.
FIG. 4 is a longitudinal sectional view of a main part showing a conventional structure.
FIG. 5 is a top view of a part of FIG. 4;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Anode target 11f ... X-ray focal track surface e ... Electron beam 16, 17 ... Cathode 18 ... Vacuum container 18a ... Metal container part 11m, 11n ... Recessed part

Claims (2)

An X-ray focal point on the anode target, comprising: a disc-shaped anode target arranged in a vacuum vessel; and a cathode arranged to emit an electron beam toward the X-ray focal plane of the anode target. In a rotary anode type X-ray tube having a configuration for taking out an X-ray beam generated from a predetermined direction for the purpose of use,
Said anode target, at least the inner and outer regions adjacent to the X-ray focal track surface, the recess does not foresee from the central axis of the take-out direction of the X-ray beam has been formed, the concave portion of the outer region outside A rotating anode X-ray tube characterized by being gradually shallowly recessed toward the periphery . 2. The rotary anode X-ray tube according to claim 1 , wherein the anode target is cut out along the direction of the rotation axis from a position corresponding to the outer peripheral edge of the X-ray focal track surface.

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