US2097002A

US2097002A - X-ray tube

Info

Publication number: US2097002A
Application number: US747103A
Authority: US
Inventors: Thaller Rudolf
Original assignee: Individual
Current assignee: Individual
Priority date: 1934-04-14
Filing date: 1934-10-05
Publication date: 1937-10-26
Anticipated expiration: 1954-10-26
Also published as: FR776420A; BE404912A; GB432154A; NL40068C

Description

Oct. 26, 1937. R. THALLER 2,097,002

X-RAY TUBE Filed Oct. 5, 1934 5 a /er- Patented Oct. 26, 1937 UNITED STATES PATENT. OFFICE 4 x-aAY TUBE Application October-5, 1934, Serial No. 747,103

In Germany-April '14, 1934' 3 ims. -1 F351 In all the known constructions of X-ray tubes the sharpness of the image at every point o'fthe image carrier (photographic plate, fluorescent screen and the like) depends onthe angle of inclination of the focal surface to the ray leading to said point. If, for example, the focal point is band-shaped there is found in the X-ray photograph a noticeable and often very detrimental falling off of sharpness from the middle towards the sides and especially from the part of the image turned towards the anode to the part fect if the focal surface makes an angle (gener--- ally between and 80) with the image plane.

Strictly speaking only a point focus or a spherical focal surface can give an astigmatic image. Cir-- cular or annular foci with surface parallel to the image plane would produce practically anastigmatic. images but they would have .to be. very small in viewof'the total sharpness which'de creases. with the size of focus. In order not to diminish too much the mean total sharpness of th'eimage linear foci have been used. Thiscon struction of tube however is very liable toastigmatism'... The present invention relates to an X-ray tube of high output which will take a much higher load than the ordinary linear focus tube and is not less satisfactory than the tubes with rotating anode for instantaneous exposures, but which operates without astigmatism. In this new tube the surface which emits the X-rays is the outer surface, which is uniformly bombarded with electrons, of a narrow cone made of a metal of high melting point, for example tungsten, having an apex angle of about 30 or less and having its axis at right angles to the image plane in use. With this arrangement the effective imageforming focal surface appears substantially as a circle from every point of the image plane.

The invention is illustrated by way of example in the accompanying drawing.

Fig. 1 shows the X-ray tube with parts broken away.

Fig. 2 explains the action of the conical anode.

Fig. 3 shows a detail on a large scale.

Fig. 4 is a section along line 4-4 of Fig. 3 on a smaller scale,

Figs. 5 and 6 show diagrammatically other possibilities of arranging auxiliary electrodes.

Figs. '7 to 9 show modified details.

According to Fig. 1 the conical anode a is secured to the anode support A which is fixed in the-glass bulb R of" the X-ray tube in sucha manner that the cone axis is at right angles to the tube axis. In order that the conical anode a may be uniformly bombarded with cathode rays (electrons) several glow cathodes n surrounding the anode a and preferably consisting of helically wound wire may be used which are arranged in a collecting device hprovided on the cathode support K.

an the diagrammatic explanatory Fig. 2, bis the edge ofrthe base of the effective part of the, anode cone, c is the cone axis, the extension of which inters'ects the image plane'g in the point e. The points in which the separate generating lines of the'cone a when produced beyond its apex, intersect the image planeg form a circle 1 on this plane. From all points lying within the circle* I the'b'asecircle b' of the anode cone a isncompletely visible. The effective image-formirlglfocal surface 'is always circular although the effectivelfocal surface is the conical surface seen from abov'et Since the base circle I) of the cone is parallel 'to' the image plane, the foreshorteni-ng of .thediame'ter d as" observed from a pointon thecir'cle ids-very small. If, for example, the

vertical. angle or of the cone is 22*, the greatest foresho'rtening of the diameterdof the base of the cone as seen from a point on the circle I is the cone as seen from a point on the circle is less than 0.12 mm. with a cone having a base of,

for example 6 mm. diameter. Consequently the sharpness of the image is practically uniform within the circle f. Furthermore the effective electron emitting anode area corresponding to the conical surface is more than five times the area of the base circle, thus procuring a relatively high radiating intensity as compared with the small apparent area of the focal spot, which ensures a most sharp image.

In practice the cone need not have a straight generating line; this may be somewhat curved, as shown in Fig. '7, so that the conical surface is for instance a hyperboloid of revolution.

The cone may be cooled by radiation or by conduction. In the latter case the cone may be embedded in a material of good conductivity, such as copper. If the cone a is made hollow it may be cooled by means of a medium circulating rapidly in its interior. This modification is I shown in Fig. 8, according to which the anode support A is also hollow and a tube q for supplying a cooling fluid is arranged within its hollow space p and introduced with its end into the hollow space r of the anode a, so that fluid may circulate as indicated by the arrows.

The collecting device illustrated consists of a drum-like metal casing h, the axis of which coincides with the axis of the cone. The plain wall 2 of the casing which faces the base of the done has an opening is for the conical anode a. The other end wall 7 of the casing has an opening m opposite the apex of the cone a for rays to pass out. The metal casing his given a potential opposite to that of the anode. The opening it is made so large that with a high vacuum no discharge can take place directly between the anode and the casing.

In the construction according to Figure 3 the axes of the helical wires n which are in a plane with the axis of the cone a are parallel to the axis of the cone. They may also be inclined to it so as to intersect each other; for example they may be parallel to the opposed generating lines of the conical surface, as shown in Fig. 9. Experiments have shown that when the drum-like collecting device is correctly dimensioned the axes may run parallel to the coneaxis without the bombardment of the conical surface becoming non-uniform, whether with a small emission (currents of a few mA) or with a, very high emission (currents'up to and over 1,000 mA).

The glow wires 11. are shown in Fig. 3 as being connected with the drum h of the supporting device at their left hand ends. In consequence thereof they are connected in series, if their free right hand ends are connected with the terminals of the source of heating current, and have the same potential as the collecting device. A connection in parallel may be obtained, either without changing anythingin Fig. 3, by connecting the free ends of the wires with one and the same terminal of the heating current source and the drum h. with the other terminal, or by passing the left hand ends of the wires n with proper insulation through the wall of the drum h and connecting both ends of each wire directly with the terminals of the current source. In this case of course the potential of the glow wiremay be different from that of the collecting device.

conical surface of the anode and more particularly to. obtain a more uniform bombardment of the cone surface.

When using only two diametrically opposite glow wires the drum h is preferably given, as shown in Fig. 4, an oval cross-section with the longer axis in the plane passing through the two glow wires. If more than two glow wires are used the drum is preferably made of circular cross-section. 1

I claim:

1. Riintgentube comprising an envelope, an

anode having a focal portion in the form of .a cone, said cone having an apex angle of not more than 30, a collecting device in the form of a metal casing surrounding said cone and having a radiation opening axially opposite'the apex of the cone, and a plurality of substantially equidistant glow cathode wires arranged within said metal casing and between its shell and said anode cone and extending longitudinally of said cone. 2.'R6ntgen tube as claimed in claim 1, comprising two glow cathode wires the axes of which lie approximately in a plane with the axis of the anode cone, and a plurality of auxiliary electrodes also arranged within said metal casing between its shell and the anode cone and also extending longitudinally of the cone.

3. Rontgen tube as claimed'in claim 1, comprising two glow cathode wires the axes of which a lie .approximately in a plane with the axis of the cone, said metal casing being of oval cross-sec tion with the longer axis coinciding approximately with the common plane of the cone axis and'the glow .wire axes.

' RUDOLF II-IAlL-LER.