US3668454A

US3668454A - Fine focus x-ray tube

Info

Publication number: US3668454A
Application number: US17571A
Authority: US
Inventors: Yoshihiro Shimura
Original assignee: Rigaku Denki Co Ltd
Current assignee: Rigaku Denki Co Ltd
Priority date: 1969-08-05
Filing date: 1970-03-09
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06

Abstract

The present invention provides a fine focus X-ray tube with improved directivity wherein extremely intensive X-rays are generated from a fine focus and the position of the focus can be moved finely.

Description

United States Patent Shimura June 6, 1972 54] FINE FOCUS X-RAY TUBE [56] References Cited [72] inventor: YOSl'lihilO Shimura, Tokyo, Japan UNITED STATES PATENTS [731 Assignee Rigak Denki Limited Chiyoda' 2,168,780 8/1939 Olshevksy ..313/59 x Japan 2,866,113 12/1958 Cosslett [22] Filed: Mar. 9, 1970 2,046,808 7/1936 BOuwetS et a] ..3 1 3/57 [2]] Appl' 17571 Primary Examiner-Robert Sega! [30] Foreign Application Priority Data Assistant Examiner-Darwin R. Hostetter Aug. 5, 1969 Japan ..44/6l44l Bremer NOV. 17,1969 Japan ...44/9l454 ABSTRACT [52] U.S. Cl. ..3l3/57, 250/99, 250/65 R. The present invention provides a fine focus X-ray tube with 313/330 improved directivity wherein extremely intensive X-rays are [51 1 Int. Cl. generated from a fine focus and the position 0f the focus can of Search ..3 l 59, 60, 55, be moved fine]y 3 Claims, 8 Drawing Figures SHEET 10F 2 PATENTEDJUN 6 I972 FIG. I

FIG. 2

PATENTEUJUN 6 I972

sum

2 or 2 FIG. 5

FIG. 8

'FIG. 7

FINE FOCUS X-RAY TUBE The present invention relates to a fine focus X-ray tube.

X-ray microscopes and other measuring or observing apparatuses require a source of X-rays having an extremely small focus, for instance, of not more than dozens of microns. Especially in case of X-ray microscopes, it is necessary to arrange the specimen near the focus, so that X-rays must be taken out from the reverse side of a foil target. For this purpose, a fine focus X-ray tube wherein a thin foil target is arranged between thick metal bases which have a conical hole has been presented. A construction comprising a metal base with a truncated conical hole and a foil target stuck on the inside surface of said metal base is also known. Since the foil target is cooled quite well in this way, the density of electron rays can be increased and so intensive X-rays can be generated. However, the specimen cannot be brought enough close to the focus of X-rays, for a thick metal base is arranged outside the foil target. Further, as the X-rays used are only those from the foil target, there is a limit to the intensity of generated X-rays.

An object of the present invention is to provide a fine focus X-ray tube wherein the intensity of X-rays is increased by using the X-rays not only from a foil target but also from a metal base and at the same time the directivity characteristic is improved, and wherein the distance between focus and specimen can be extremely lessened.

Another object of the present invention is to provide a fine focus X-ray tube capable of generating intensive X-rays and at the same time enabling the observing position to be moved easily and highly accurately at a high speed by including an electron ray deflecting means for adjusting the position of incidence of the electron rays.

In the accompanying drawing:

FIG. I is a longitudinal section of an embodiment of the X- ray tube according to the present invention;

FIG. 2 is an enlarged view of the target in the X-ray tube of FIG. 1;

FIG. 3 is an illustrative view showing the X-ray generating part of the target of FIG. 2 and the X-ray radiated area;

FIG. 4 is a diagram illustrating the directivity characteristic of the radiated X-rays with be target of FIG. 2;

FIG. 5 is a longitudinal section of another embodiment of the present invention;

FIG. 6 is a sectional view along the line VI-VI in FIG. 5;

FIG. 7 is a sectional view along the line VII-VII in FIG. 5; and

FIG. 8 is an enlarged sectional view of part of FIG. 5.

Now referring to the drawing, FIG. 1 shows a fine focus X- ray tube as an embodiment of the present invention. A slender cylindrical gas-tight tube 3 is fixed at one end to a cylindrical gas-tight housing 2 containing an electron gun I and a target base 4 is arranged at the other end of said tube 3. Arranged around the gas-tight tube 3 is an electron ray converging coil 5, which converges the electron rays 2 emitted from the electron gun I as shown by dotted lines so as to allow them to fall upon the base 4. The base 4 has a truncated conical hole 6, as shown enlarged in FIG. 2, across the vertex of which a thin foil target 7 is applied from the outside of the gas-tight tube 3, thereby to keep the tube 3 and housing 2 gas-tight. The target 7 can be also formed by plating the base 4. The target 7 and base 4 are made of the same metal, for instance, copper. The electron rays e are projected on the bottom side of the conical hole 6 to fall upon the inside surface thereof and the exposed part of the target 7, so that X-rays are generated from the inside surface of the hole 6 and the foil target 7. As the latter is made sufficiently thin to be permeated by X-rays relatively with ease, part of the generated X-rays go there through into the atmosphere, as shown by broken lines x. Since any base or the like is not provide outside the target 7, a specimen 8 can be set enough close to the target 7, when it is to be photographed in X-ray microphotography. Thus, an enlarged shadow image of the specimen 8 can be obtained with very great magnifications by the merrneating X-rays x.

FIG. 3 shows a relation between the distribution of the X- rays which mermeate through the target 7 to the outside and the source thereof. The X-rays generated at the foil target 7 are radiated from the reverse side thereof directly into the atmosphare. They cover, therefore, an area hatched with vertical lines, i.e. the whole area on the right of the target 7. The X- rays generated at the inside surface of the truncated conical hole 6 provided in the base 4 permeate through only the exposed part of the target 7 at the vertex of said hole to go out into the atmosphare, so that they cover an area hatched by right or left inclined lines. The directivity curves of the generated X-rays are shown in FIG. 4. The X-rays generated at the target 7 and projected from the reverse side thereof into the atmosphare are considered to have substantially a directivity shown by a courve 9, for they are more and more absorbed with decreasing angles thereof against the surface of the target. On the other hand, the X-rays generated at the inside surface of the hole 6 and projected through the exposed part of the target 7 into the atmosphare possess a directivity shown by a curve 10 or 11. Derived from the curves 9, l0 and 11 is a total directivity curve 12, which has a very wide angle of divergence. Besides, the X-rays are projected with substantially equal intensities in all directions. While explanations here have been made on the assumption that the X-rays generated at the inside surface of the hole 6 permeate through the target without scattering, a considerably great amount of scattered X-rays results, in practice, in the target. These scattered X-rays possess a directivity substantially equal to the curve 9, so that the intensity of the X-rays perpendicular to the surface of the target 7, Le. in the axial direction of the gastight tube 3, is additionally increased, which was confirmed also in experiments.

A known X-ray tube so constructed that electron rays are projected onto the target 7 of FIG. 2 from the right side thereof to take X-rays from the hole 6 has no possibility of generating X-rays at the inside surface of the hole to make use of them. In another known X-ray tube, a base is arranged where oblique lines are drawn on the right side of the target in FIG. 3. Hence, the X-rays generated at the inside surface of the hole 6 and having directivities as shown by the curves l0 and 11 in FIG. 4 are cut off and so their effective use is impossible.

In the X-ray tube according to the present invention, a truncated conical hole 6 is formed in a target base 4 and a thin foil target 7 is arranged at the vertex of the hole 6. In addition, at least the inside wall of the hole 6 is made of the same material as the target. Electron rays are projected onto the base on the bottom side of the hole 6. Thus, the X-rays generated at the inside surface of the hole 6 and permeating through the target 7 can be effectively made use of. Hence, extremely intensive X- rays can be generated and emitted directly into the atmosphare from a very fine focus corresponding in size to the dimensions of the vertex of the hole 6. The directivity characteristic is also improved to permit projection of X-rays equal in intensity in all directions. Further, since no target base is provided on the atmosphare side of the focus of X-rays, the distance between specimen and focus can be made extremely small.

Referring now to FIGS. 5 8 showing another embodiment of the present invention, the arrangement of this apparatus differs from that of FIGS. 1 4 in the fact that an electron ray deflecting coil 13 is provided around the gas-tight tube 3 together with the electron ray converging coil 5 and that an inwardly opened V-shaped groove 14 is formed in the target base 4 in such a way that a narrow slit 15 is formed at the vertex of said groove.

Electron rays e are projected from an electron gun (not shown) in parallel to the axis of the gas-tight tube 3 and converged by the coil 5 to plate-like electron rays e.

However, the electron rays 2 are deflected by the deflecting coil 13 in the direction of the groove 14, so that they can fall upon the target at different points, as shown by dotted lines 2,, e, and e when current through the coil 13 is adjusted. In this way, the electron rays e fall upon the exposed part of the target 7 only at one point p and this point of incidence p travels as shown by arrows in FIG. 7 when current through the deflecting coil 13 varies. Hence, when a specimen 8 is arranged behind the target, as shown by a dash-and-dot line in FIGS. 5, 6 and 8 and an X-ray film 16' is arranged further therebehind, the X-rays generated from the point p permeate through the specimen 8 to enter the film 16, thus causing an enlarged shadow image of the specimen to be photographed.

When the width of the slit at the vertex of the groove 14 is made, for example, several microns and the electron rays e are converged to the form of a plate of several microns in thickness, a fine focus of substantially several microns in diameter can be formed and also X-ray microphotographs having an extremely high resolution can be taken.

By adjusting the current through the deflecting coil 13 to move the position of focus p, any portion of the specimen can be selected for observation in the direction of the groove 14.

' As described before, this positioning is carried out by varying the coil current, so that it is extremely fine, smooth and safe. in addition, if necessary, alternating current may be applied to the deflecting coil 13, thereby to reciprocate the focus of X- rays p at a high speed. Since the foil target 7 is attached to a thick metal base 2 of high thermal conductivity and the edge of the focus is in direct contact with the base, the heat generated from the focus dissipates quite well, so that the current density of electron rays e can be made extremely high. Further, the electron rays e fall also upon the inside walls of the V-shaped groove 14 to produce X-rays therefrom. Part of the X-rays are emitted through the target 7 attached across the slit 15 at the vertex of the V-shaped groove 14. Namely, the X-rays generated at the target itself and those generated at the inside walls of the groove 14 and passing through the slit 15 enter the specimen 8. Hence, extremely intensive X-rays can be obtained in co-operation with the possibility of increasing the density of electron current.

In this way, the X-ray tube according to the present invention is not only capable of generating extremely intensive X- rays from a fine focus, but also permits the position of focus to be adjusted finely and smoothly and, if necessary, to be moved at a high speed. Hence, no large and highly accurate equipment for travelling the specimen mechanically is necessary.

What is claimed is:

1. A fine focus x-ray tube comprising a cylindrical gas-tight tube, a target base arranged at one end of said gas-tight tube and having an opening containing a vertex, a target covering the vertex of said opening and being sufficiently thin to be permeated by X-rays, the inside wall of said opening being made of the same material as said target, an electron gun generating electron rays to be projected from the inward side of said opening onto the inside surface of said opening and the exposed part of said target at said vertex, and a specimen being spaced beyond said target, said specimen being photographed in x-ray microphotography by the X-rays generated at the inside surface of said opening and projected into the atmosphere through said target from the reverse side thereof.

2. The fine focus X-ray tube of claim 1 wherein said opening containing a vertex is a truncated conical hole.

3. The fine focus X-rays tube of claim 1 wherein said target base arranged at said one end of said gas-tight tube possesses as said opening an inwardly opening V-shaped groove with a narrow slit at the vertex thereof, and wherein an electron ray deflecting means is provided outside said gas-tight tube for adjusting the position of incidence of electron rays upon said target by deflecting said electron rays in the direction of said groove.