US2046808A

US2046808A - X-ray tube

Info

Publication number: US2046808A
Application number: US741838A
Authority: US
Inventors: Bouwers Albert; Halberstadt Heinrich
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1933-09-06
Filing date: 1934-08-28
Publication date: 1936-07-07
Anticipated expiration: 1953-07-07
Also published as: BE404933A; FR423567A; GB423567A; FR776893A

Description

Patented July 7, 1936 'i UNITED STATES PATENT CFFICE x-RAY TUBE Application August 28, 1934, Serial No. 741,838

f In Germany September 6, 1933 8 Claims.

The present invention relates to X-ray tubes having perforated anodes, and more particularly to a novel arrangement and .shape of the electrodes of such tubes to obtain a sharp focal spot.

We are aware that it has already been proposed to provide X-ray tubes with perforated anodes, from which the X-ray beam emerges. Such hollow anodes have been used in connection with two constructions. In one such construction the cathode was disposed Within the hollow of the anti-cathode. Such a construction has various drawbacks. Y

For example a sharp focus cannot be obtained by this construction, because the conical target must be relatively wide. The construction is of use for therapeutic X-ray tubes only, for which a small lfocus is not required. l

According to the other construction the anode has two excavations arranged side by side, one enclosing the cathode filament `and the other containing the target.

The cathode rays inthis construction pass through an aperture in the .partition between the two excavations. This construction permits of making a sharp focus, but theV cathode rays can only strike a section of the inner Wall of the target excavation.

In each of the constructions referred to the beam of X-rays used like in tubes of the conventional type, forms an angle of about 90with the cathode rays.

Itis one object of the present invention to make an X-ray tube in which there is only a slight difference between the Adirection of the useful X- rays and the cathode rays producing them.

Another object of the invention is to increase the output of an X-ray tube.

A further object of the invention is to improve the sharpness of X-ray photographs by decreasing the size of the focus projection. i

Another object of the invention ls to avoid optical distortion of the focal spot.

Our invention is particularly adapted for X- ray tubes operating at high voltages, of about 100 kilovolts and more.

According to the invention, the anode is provided with a passageway, preferably with a conical or funnel-shaped passageway; the conical inner surface of the' passageway acting as the target of the tube. The electron-emitting cathode is disposed outside of the anode and opposite the smaller end of the passageway, and the electron beam or cathode rays emitted by the cathode are directed through the smaller end of the passageway toward the target surface of the an- (Cl. Z50-35) ode, to strike same at a Very acute angle. Thereby the X-rays leave the tube substantially in the same direction at which the cathode rays leave the cathode and at the same time a very sharp focal spot is obtained.

According to a particular embodiment of our invention the cathode rays are so directed toward the passageway of the anode, the passageway having the shape of a truncated cone, that the cathode rays converge and cross each other in l0 the vicinity of the entrance of the conical passageway.

The invention, however, is not limited to a construction in which the cathode rays converge after leaving the cathode.

Such an arrangement, in which the X-ray beam has substantially the same direction as the converging cathode rays, results in a very simple and compact construction. Any desired convergence of the cathode rays can be obtained, even in the case of extremely high voltages, by suitable shapes and relative disposal of the cathode and anode structures. The opposing surfaces of the cathode and anode structures are preferably parallel and the anode is provided with an opening, preferably with an annular opening, for the passage of the cathode ray beam.

The cathode structure is preferably such as to form a narrow annular source of cathode rays. For this purpose a flamentary cathode forming an annulus may be used, the lament being disposed in a concentric narrow annular groove formed in a portion of the cathode structure, which portion acts as the focussing device.

Y With a conical surface of the focussing device and with a corresponding conical anode surface opposing same, the direction of the electric field existing between these two surfaces and thus the initial direction and convergence of the cathode rays, dependsV on the slope of these conical surfaces.

By varying the convergence of the cathode ray beam a concentrated or diffused impact of the cathode rays on the target can be obtained. By meansof such convergence of the cathode rays it is possible to obtain a sharp focal spot of the X-rays, in a very eiiicient and advantageous manner.

A very high efficiency is obtained by so directing the cathode ray beam toward the target as to impinge thereupon at a very acute angle.

We are aware that is has been already proposed to direct cathode rays at an'acute angle toward the target. This, however, has been for the purpose of obtaining a narrow elongated focal spot. However, a flat or narrow elongated focal spot has the drawback of optical distortion; i. e. when viewed from different portions of the image, its dimensions do not appear the same.

This drawback does not exist with a circular focal spot, as obtained in arrangements in accordance with the invention, which provides not only for a very high eiciency and highly satisfactory heat distribution over the target, but also insures an unusually high quality of definition.

As stated, in accordance with a preferred embodiment of our invention, the cathode rays may be caused to converge and after crossing each other impinge at a highly acute angle on the inner wall of the passageway, which forms the target and which as stated, may have the shape of a truncated cone. By proper selection of the slope of the opposing cathode and anode surfaces, the diameter of the passageway may be made quite small so that the optically operative area of the focal spot is of the same order of magnitude as that of a band shaped focus. At the same time the load is distributed over the entire surface of the target. This permits a very high loading of the tube, and because ofthe acute angle of incidence of the cathode rays, the effect of the Y-rays is about 30% higher than can be obtained in the case of vertically incident rays. Y

Our invention may have various constructonal executions. Accor-ding to one simple embodiment of our invention, the X-ray tube is given a cylindrical shape with the X-rays emerging at one end of the tube in the axial direction thereof. The target surface, formed as a truncated cone, may consist of tungsten or similar refractory metal, which is embedded in a solid metal block of good heat conductivity for instance, copper.

On its face opposite to the cathode, the anode block may be provided with a surface which is so shaped, for instance sloped or curved, as to provide for a converging field. Furthermore, the anode block may be in intimate heat-trans'- ferring relationship with a metal portion of the X-ray tube envelope so that the heat developed in the target can be suitably and efficiently carried away to the outside. To promote heat dissipation the above referred to metal envelope portion may be provided with cooling fins 0r other suitable cooling means. In a tube of the type just described, the metal portion and the anode are preferably grounded.

According to another embodiment of our invention, the X-rays are caused to emerge from the tube in a lateral direction, thus perpendicularly to the axis of the tube. In such an arrangement the anode may comprise a large volume body disposed coaxially with the tube and provided with an extending portion, opposing the cathode, which extension carries the hollow target. The cathode thereby is not coaxial with the tube. In such a tube the voltage between the electrodes may be suitably subdivided by providing around the discharge space of the tube a metal waist section or by providing this portion of the tube with a conductive coating.

The invention will be more clearly understood by reference to the accompanying drawing, which represents by way of example some embodiments of our invention, and in which Figure l is a sectionized side view of an anode and cathode structure illustrating the principle of our invention, p

Fig. 2 is a sectionized side Yview of an Xray tube embodying the invention in whichthe X` rays emerge at the anode end of the tube in an axial direction,

Fig. 3 is a sectionized side view of an X-ray tube showing another embodiment of the invention, in which the X-rays emerge laterally from the central portion of the tube.

Referring to Fig l, an anode body 2 consisting of a metal of high heat conductivity, for example of copper, is provided with a truncated cone-shaped passageway I5, the inner surface l of which is formed of a refractory metal, for instance of tungsten or other suitable refractory material and acts as the target 6. The upper face I3 of the anode body is conically shaped. The anode body 2 is provided in its upper por- 1 tion with a cavity 32. Provided in the face I3 of the anode body 2 is an aperture 5, forming a substantially continuous annular opening connecting the cavity 32 to the discharge space and providing a passage for the cathode rays.

A cathode body I is arranged opposite the conical surface I3 of the anode body 2 and is provided with a conical surface 36, substantially parallel to the opposing anode surface I3. Arranged in the cathode body is a cavity 4 within whichis disposed an incandescent lament 3, which emits the electrons forming the cathode rays, and a metal body 31, the conical surface 38 of which corresponds with the surface 36 of the body I. Glass parts 39 and 40 are hermeti- 3 cally sealed to the anode and cathode bodies and form the usual insulating connection of the electrodes.

The direction of the cathode rays is determined by the electric field, whereby the lines of force are perpendicular to the cathode and anode surfaces. The cathode rays converge in the vicinity of the upper end of the passageway I5, after which they diverge and impinge upon the target 5 at a small angle with the surface thereof. The X-rays generated atthe target 6 emerge through the larger end of the passageway I5 and pass through a window 'I provided for the exit of the X-rays.

In Fig. 2 the X-ray tube comprises an envelope 8 of vitreous material to one end of which is hermetically sealed a metallic ring 9, made for instance of chrome iron. The ring 9 is cast in a copper body 4I serving as an anode and forming the bottom end of the tube.

Supported by a re-entrant portion of the envelope 8, is a cathode body I2, provided with a conical'cavity 42. Arranged in the cavity 42 is an annular groove 33 Within which is disposed an incandescent filament II, which emits the electrons forming the cathode rays. Passing through and hermetically sealed in a pinch I0 are lead wires 30 and 3I, which are electrically connected to the two ends of the incandescent filament and may also act as supports of the cathode body. The lead 3I is insulated from the cathode body whereas in the arrangement s hown the lead 30 is electrically connected therewith.

The anode body 4I has, similarly to the body 2 shown in Figure 1, a conical surface portion I3 substantially parallel to the opposing surface of the cathode body and has an annular aperture for the passage of the cathode rays, as well as a conical passageway I5 comprising the target 6. The cathode rays converge in the vicinity of the upper end of the'passageway I5', after which they impinge at an acute angle upon the surface of the target 6 'Ihe Xarays generated on the target emerge through the large end of the passageway and Vleave the-tube through 'the window I6. I

To readily dissipate the heat producedy inthe target, the anode body 4l is provided with a plurality of cooling ns 34. l

Fig. 3 shows an X-ray tube in which the X-ray beam has a direction substantially perpendicular to the axis of the X-ray tube. The X-ray tube has an envelope comprising two re-entrant glass portions Il-I'L Between the glass portions l'I-I 1 and hernietically sealed to the edges thereof, is a substantially central metallic wall sleeve I8, made for instance, of chrome iron, in which is hermetically sealed a ray-emitting window I9 for the exit of the` X-rays. v

By means of a metal tubular member 46 the cathode body 22 is supported from a pinch 26 carried by the re-entrant part of one of the glass portions I1 and two lead-in wires 43 and 44 sealed in the pinch 20, serve as electrical connections to the cathode. The connection of the leads to the cathode and the filament 2l are similar to those shown in Fig. 2 and do not require further description.

From the other end of the tube is supported an anode body 23 consisting of a block or rod of good heat-conducting metal, for instance of copper, which may be welded, preferably by the intermediary of a chrome iron member 45, to the corresponding rie-entrant part of the glass portion Il. The body 23 extends with a projection 24 towards the cathode, the projection 24 having substantially the same form as the anode structure shown in Fig. 2.

It should be well understood that in the drawing the X-ray tubes are shown more or less schematically, the emphasis being laid on such details only as are necessary to clearly understand the principle underlying the present invention.

While we have described our invention in connectie-n with a specific application and with regard to specific embodiments, we do not wish to be limited thereto, but desire the appen-ded claims to be construed as broadly as permissible in view of the prior act.

What we claim is:

l. An X-ray tube comprising a cylindrical envelope, an anode structure and a cathode structure disposed adjacent to each other and forming a discharge space, said cathode structure having a concave conical surface opposing the anode structure, and said anode structure having a conical surface opposing the cathode structure, said cathode structure having a cavity with a substantially ring-shaped opening, a ring-shaped electron-emitting filament disposed in said cavity, said anode structure having an inner cavity connected to the discharge space by an annular opening in the conical surface of the anode structure, and a truncated conical passageway connected with said inner cavity and forming a target for the anode, the cathode rays passing from the electron-emitting filament to the target through the ring-shaped opening, the annular opening and the inner cavity of the anode, and intercepting each other in the vicinity of the cathode end of the conical passageway, and the X-ray beam emerging from the anode end of the tube in a direction substantially corr-esponding to the axis of the tube.

2. An X-ray tube comprising an envelope, an anode structure and a cathode structure adjacently disposed therein, the cathode structure having a concave conical surface opposing the anode structure, and the anode structure having a corneal surface substantially parallel to the surface of said cathode structure, said cathode structure having a groove in its surface, an electronemitting filament disposed therein, said anode structure having a truncated conical passageway therein with its smaller end opposing the cathode structure, the surface of said passageway forming a target, the cathode rays passing from'the cathode structure to the target through the smaller end of said passageway, and the X-ray beam emerging from the larger end of said passageway. .Y r

3. An X-rayr tube comprising an envelope, an anode structure and a cathode structure adjacently disposed therein, the cathode structure having a concave conical surface opposing the anode structure and the anode structure having a conical surface substantially parallel to the surface of the cathode structure, said cathode structure having a circular opening in its surface, a ring-shaped electron-emitting filament disposed in said cathode structure, said anode structure having a truncated conical passageway therein with its smaller end opposing the cathode structure, the surface of said passageway forming a target, the cathode-rays being convergent to intersect in the vicinity of the smaller end of said passageway and subsequently being divergent to impinge at an acute angle upon the target.

4. An X-ray tube comprising an envelope, an anode structure having a portion coaxially disposed in said envelope and a projecting portion forming the active portion of the anode structure, a cathode structure disposed adjacent to said active anode portion to form therewith a discharge space, said cathode structure having a concave surface and the active anode portion having a surface opposing and substantially parallel to said concave surface, said active anode portion having a cavity connected to the discharge space by an opening and having a truncated conical passageway connected by said cavity to said opening, the surface of said passageway forming a target for the anode, the cathode rays passing from the cathode to the target through said opening and cavity, and the X-ray beam emerging from the tube in a direction which is substantially perpendicular to the axis of the tube.

5. An X-ray tube comprising an envelope, an anode structure having an interrupted convex surface and a hollow target portion, and a cathode structure disposed outside said anode structure and having an interrupted concave surface,

said surfaces having a common axis and beingv substantially parallel to each other with their interruptions in line to form a discharge gap,

said cathode structure comprising an electronemitting element disposed to emit electrons passing through the interruptions in said surfaces and striking the hollow target at an acute angle to generate thereon X-rays which emerge from the tube in substantially the direction of the common axis of said surfaces and away from the cathode structure.

6. An X-ray tube comprising an envelope, an anode structure having a truncated-conical passageway whose inner surface forms a target, a cathode structure comprising means to generate a beam of primary electrons, said cathode structure being disposed outside the anode structure and spaced therefrom to form a discharge gap defined by parallel conical surfaces, said surfaces being disposed coaxially with said passageway and having mutually-corresponding apertures, the electrons emitted by said means passing through said apertures and entering said passageway through its end opposing said cathode structure to generate on said target X-rays which pass through the opposite end of said passageway.

'7. An X-ray tube comprising an envelope having a vitreous portion, an anode structure forming a, portion of said envelope and having external cooling means connected thereto, a cathode structure comprising a hollow metal member and an electron-emitting element disposed therein, said member having a concave surface opposing said anode structure, said anode structure having a conical surface opposing said cathode structure and being provided with a cavity having a truncated conical target portion coaxial with said conical surface with its smaller end adjacent the cathode structure, the opposing surfaces of said anode and cathode structures being provided with mutually-corresponding apertures through which the cathode rays emitted by said element pass from the cathode structure to said target portion.

8. An X-ray tube comprising an envelope, an anode structure provided With a cavity having a truncated-conical target portion, and a cathode structure disposed outside of said anode structure, said cathode structure having a cavity and an electron-emitting element disposed therein, said structures having substantially parallel opposing surfaces, the surface of the cathode structure opposing the anode structure being concave and the surface of the anode structure opposing the cathode structure being convex, said surfaces being provided with mutually-corresponding apertures communicating with said cavities, the cathode rays emitted by said element passing through said apertures to impinge at an acute angle upon the Wall of said truncated-conical portion and to generate thereon X-rays having substantially the same direction as the axis of said truncatedconical portion.

ALBERT BOUWERS.

HEINRICH HALBERSTADT.