US1685928A

US1685928A - X-ray tube

Info

Publication number: US1685928A
Application number: US476155A
Authority: US
Inventors: Morrison Montford
Original assignee: Individual
Current assignee: Individual
Priority date: 1921-06-09
Filing date: 1921-06-09
Publication date: 1928-10-02
Anticipated expiration: 1945-10-02

Description

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. of tgen or lf-rays.

aanname ana .vaat a, raar. in tratta Vllhe present invention relates to vacuum devices and more particularly to certain irnprovements in apparatus for the generation dn object of the invention herein described is the provision of a more powerful lf-ray apparatus.

Another object of the present invention is the provision of an X-ray device which will afford safety bot-h to an operator of the device and to a patient exposed to the action of the same.

Another object of the present invention is the revision of andi-ray device which will pro uce clear definition in a radiograph.

it further object of this invention is the pro vision of a more durable X-ray tube.

Other objects of this invention will be apparent from the following description.

ln the continuous advance of the lf-ray art it is desirable to construct increasingly more powerful X-ray generating units. Previous X-ray devices have been limited in voltage by reason of the excessive stresses set up by electrostatic fields resulting from the very high voltages required in modern high powered X- ray tubes. 'lhese stresses result in strains which finally end in a uncturing of the enclosing envelope and t ereby terminate the usefulness of the device. 'lhe failure of an lli-ray tube in such manner is not only uneconoinical but ina prove injurious to persons in the vicinity o the tube.

ln the past, accidents of a serious and even fatal nature have resulted from an improper constructionl of X-ray tubes. 'lliis applies particularly to patients in the process of being subjected to X-rays. ln the use of a tube of the present invention, such dangers are materially reduced.

lli-ray tubes of the prior art have been objectionable, especially for therapeutic p-urposes, in that the X-radiation therefrom has been heterogeneous. lt is known that radiation from an X-ray tube contains rays of different hardness, that is to say, rays of varying penetrative power. For certain purposes, the hard rays alone are necessary and desirable; in such cases it is highly desirable to eliminate the soft rays. An instance of such a require ment may be cited as being existant in the therapeutic use of X-rays where it is desirable to treat deep-seated tissue, in which case hard rays are necessary; however, a simultaneous gene-ration of the softer rays reachI the more supercial layers of tissue and it. is

the same.

lt will, therefore, at once be appreciated that these softer rays should be eliminated and 1t will be apparent from the following description that l lhave devised means for preventin the preyudicial action of the same. 'lhis d other novel features and benefits of my invention will be explained in connection with the description of the accompanying drawing, the single figbureof which is a sectional side elevation of an X-ray tube embodying my invention.

Referring to the drawing, the X-ray tube shown is provided with an evacuated sealed envelope l consisting, for example, of glass suitable both from the mechanical stand oint and for the transmission o-f X-rays a-nifinto whlch are scaled a high-tension electrode 2 and a cathode 3 having their vertical axes coincident ivith the corresponding axis of the envelope. 'lhe form of the envelope provided for the X-ray tube of the present invention is a novel feature in X-ray devices, and valuable results are obtained by the use of such an envelope.. 'lhe bulb is of such configuration that its surfaces substantially conform to the lines of force representing the electric eld in which it is disposed and, by possessing properly proportioned radii of curvature and beino' symmetrical with respect to the vertical axis and to the electrodes (as shown) ,it avoids the concentration of suoli lield at a point and the consequent liability of the glass to puncture. When made in such manner, higher voltages may be used, whereby more powerful lf-rays may be generated than in prior devices. Further, a smaller bulb may be used for an X-ray tube of given input and this affords advantages and econonues over devices of the prior art.

lt will be app-arent that the fo-rm of the bulb, preferably being substantially that of an ovoid, with all outer surfaces convex and its axis in line with the electrodes, will vary somewhat with different conditions of use and it is to'be understood that the exact form of the bulb is not confined to the outline shown in the drawing, which is illustrative only.

The. position of the anti-cathode 2, which is preferably a hollow cylinder of refractory material, such as tungsten or molybdenum, and which is sealed into the envelope l by means of the press fl, is a feature of the present K-ray tube; being directed awafrom the object of the X-rays, there is litt e dandit dll

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ger of personal injury resulting from contact with a high-potential electrode. The anti-cathode 2 is further characterized by the novel form of its lower end 6 which forms a target Where X-rays are generated. The form of target provided in a tube o f the present invention and hereinafter described, overcomes a defect in previous X-ra-y targets by which a portion thereof was in danger of melting when the X-ray tube was run at an over load. This liab-ility of fusion occurred particularly at the thin edge of the anti-cathode which resulted from truncation of this member at an angle to its longitudinal axis. The surface of the target 6, from which X-rays originate, is given, according to thel present invention, a convex surface which may be hemispherical. That is to say, the surface connecting the body of the anticathode with its target is preferably continuous so as to be free from sharp angles. Integrally affixed to the target 6 is a body0 of refractory metal 7, such as tungsten, which constitutes the focal spot or point of origin of the major portion of X-ra-ys. Preferably, the focal body 7 is inset so that its surface forms part of the hemispherical surface of the target.

As stated above, the electrode 2 may be a hollow cylinder, and it is so formed for the purpose of cooling the target which may b ecome excessively hot when the tube is in operation. Cooling of the target may be effected by means of a. circulation of water or a fluid such as a gas or a. vapor contained in the cylinder, whereby heat 1s dissipated from the target by convection currents of the fluid. As one form of such heat-dissipating means, I may introduce into the cylinder a quantity of mercury 8, vapor from which ascends to the portion of the electrode which is outside the bulb and is condensed in a. radiator 11. The radiator has suilicient surface to remain, during the opera-tion of the X-ray tube, at a temperature sufficiently low to condensel the vaporized mercury, which, after condensation, falls back into the pool of liquid mercury 8.

Opposite the target 6 and having its axis coincident with the vertical axis of the X- ray tube, is a filamentary electron-emitting element 3 adapted tt be heated electrically and consisting, in this case, of a helix (3) of tungsten, tantalum or other material. It is connected to lead-in

wires

12 and 14, either one of which may be grounded, and which are sealed respectively into the envelope 1 at 16 and 17. The

wires

12 and 14 are connected to a source of current such as a battery or a transformer.

Interposed between the target 6 and the cathode 3 is a focusing cup 18 disposed with its concave surface facing the electrode 2 and provided with an aperture 9, the center of which is in alignment with theaxis of the helical cathode 3 to permit the free passage of X-rays emanating from the focal spot 7. The focusing cup may be supported in any desirable manner obvious to those skilled in the art. In t-he present embodiment of this invention, the perimeter of the opening 9 is less than the inner circumference of the helix 3. The position and size of the opening are such that only the rays originating in thc focal spot pass through, while rays generated in other portions of the target are substantially intercepted by the focusing cup. This elimination of the rays comin from parts of the target other than the ocal spot is a highly desirable improvement .in'lthat clearer images are secured of the object radiographed. The focusing cup 18, as a secondary function, also serves as a shield to prevent metallic particles which are emitted from the target 6 from beine' thrown against the glass envelope to cause tlie possible puncture of the same. The focusing device 18, which may be of molybdenum, may assume various forms and the particular form shown, naine-ly a hemispherical shell, is illustrative only, and it may or may not be electrically connected to the cathode 3 in addition,` the focusing device intercepts stray electrons emanating from the anti-cathode.

As above explained, it is frequently desirable to secure X-radiations of uniform intensity and this may be attained by absorl ing the softer rays before they reach the object of such rays. To this end I place in the path a screen capable of eliminating the undesirable rays. Such screen is shown at 19 and it may consist of a metallic plate of a material such as aluminum and may be supported in any practical manner such, for example, as by supporting means 20. The ray screen or filter 19 serves an additional function in preventing sputtered metallic particles from coming into contact with the glass envelope to the possible damage of the latter.

Interposed between the high-tension electrode 2 and the object of the X-rays, and preferably attached to the lower portion of envelope l, is a metallic shield or coating 21 shown as a dished plate, preferably conforming substantially to the envelope, in this embodiment, being shown substantially heinispherical and having an opening 22 to .permit a free passage of the X-radiation coming from the focal spot. The shield is electrically grounded and performs the function of a protective device for personal safety. And it has further utility in that the tube may be mechanically associated with its auxiliary apparatus by means of attachment to said shield, thus avoid-ing the previous rather Idangerous method of supporting the tube from a high-potential electrode by which the electrostatic lines of force were diverted and thereby caused excessive strains in the envelope. The present method of supporting lul) at, i

the device is such that the lines of force are not interfered with and the liabilit of the tube to puncture is thus materially essened.

'lhe lead 1'2 to the cathode 3 is shown passing through an aperture in the shield 2l and being insulated therefrom by a suitable bushing. 'lhe lead 14: to the' cathode may be grounded in some other way, but preferably passes through the shield 21 in electrical contact therewith, as shown.

While ll have herein illustrated and described one embodiment of'my invention, 1t is apparent that many modifications thereof may be devised Without the exercise of the inventive faculty and such modifications are to be considered as part of this invention, as set forth in the appended claims.

. 1What is claimed is:

1. An X-ray device comprising an envelope of ovoidal configuration, an anti-cathode sealed in the small portion ofsaid envelope and a cathode and focusing device disposed in the larger portion of said envelope, the shape of said envelope conformingsubstantially to the lines of force representing 'the electrical field between the cathode, focusing device and anti-cathode.

2. X-ray device comprising an evacuated envelope enclosing a. cathode and a target, common means adording personal protection and support for the envelope which consists of a grounded electro-conductive shield associated as a coating on the envelope and electrically connected to the cathode.

3. An X-ray device comprising an envelope, a target formed with a convex surface, a cooperating electronsemitting cathode, means for focusing' the electron stream, means for absorbing undesirable portions of the X-radiation and a grounded electro-conductive shield conforming to the shape of the bulbous portion of the envelope.

4. An X-ray device comprising an envelope having such radii of curvature that excessive electrostatic strains are avoided, an electronemitting cathode, an anode for emitting X- rays, means for focusing the electron stream between the cathode and the anode, means for absorbing undesirable X-rays and a grounded electro-comluctive shieldy conforming to the shape of the bulbous portion of 'the envelope and serving to afford personal protection and to support the device.

5. An X-ray device comprising an envelope, an electron-emitting cathode, an X-rayemitting target provided with a convex working surface, a heat conductive stem in one end of which said target is secured, the exposed surface of said target and the end of said stem merging to form a rounded surface, means for focusing the electron stream and means for absorbing undesirable Xsrays, and both disposed in the pat-h of the useful X-rays.

t3. An X-ray device comprising an envelope enclosing a cathode andan anode, an

f-ray target mounted in one end of said anode, said anode end and the exposed surface of said target merging and being rounded.

7. An X-ray device comprising Ian envelope, a thermionic electron-emittin cathode and a cooperating anti-cathode, a su stantially hemispherical focusin device for the electrons, said focusing 'evice being positioned with respect to said anticathode as to extend to each side thereof to such a distance as to prevent sputtered particles from the anticathode striking the envelope.

8. An X-ray device comprising an envelope, an electron-emitting cathode formed as a helix having an opening of substantial size therethrough and a cooperating X-ray-emitting anode, generating useful X-rays which pass through the electron-emitting cathode, substantially along the axis thereof.

9. An lX-ray device comprising a substantially ovoid envelope enclosing electrodes and conforming to the electrical field between said electrodes, the longitudinal axes of which substantially coincide with the axis of the l envelope, one of said electrodes serving to emit X-rays, and a substantially hemispherical focusing device located between the electrodes and extending beyond the sides of the X-ray emittingelectrode to such an extent as to prevent sputtered material therefrom striking the walls of the envelope.

10. an X-ray device comprising an envelope in'substantially the form of an ovoid with its axis vertical, a substantially helical electron-emitting cathode, the axis of which substantially coincides with the axis of the envelope, a target mounted opposite the cathode and presenting a convex surface toward the cathode and a focusing device so disposed with respect to said target as to shield the envelope from sputtered electrode material.

ll. An X-ray device comprising an evacuated envelope ovoid in shape, an electroneinitting cathode formed as a helix, an X-ray emitting target located alon' the axis of the cathode and discharging use 'ul X-rays along said axis and through the cathode, a curved shield between the anode and cathode serving to focus the electron stream and a curved shield conforming in shape to the envelope, closely embracing the lower portion thereof, serving as a support therefor and provided wi th an opening in its lower portion for allowing useful X-rays to pass therethrough.

12. An X-ray device comprising an evacu ated envelope, an electron-emitting cathode, an X-ray-emitting target located along the axis of the cathode and sending useful X-rays along said axis and through an aperture in the cathode and a shield between the anode and cathode serving to focus the electron stream from the cathode and a shield conforming substantially in shape to the envelope at the lower portion thereof and serving as a support therefor. t

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lltitlt lill 13. X-ray device comprising an evacuated envelo e, an electron-emitting cathode formed wit an aperture therethrough, an X-ray-emittino tar et located so that it will discharge usefhul -rays along the line between said cathode and target, a shield between the anode and cathode resenting a concave surface toward the ano e and electrically-connected to the cathode so that it serves to focus the electron stream and a curved shield closely embracing the lower-portion of the envelope when in a normal position and provided with 'an opening at its lower portion for allowing useful X-rays to pass there` through, said shield being grounded for the protection of persons using the device.

14. An X-ray device comprising an evacuated envelope substantially symmetrical in shape with respect to its longitudinal axis and with all surfaces of large radii of curvature, en electronemlttmg cathode therem, en X- rey emitting cathode therein located on the longitudinal axis of the envelope, an X-rayemitting target located on said axis and emitting the bulk of the X-rays generated along said axis 'so that they pass through the cathode, a focusing shield between the anode and cathode presenting a concave surface toward the anode and adapted to protect the envelope from sputtered material and a grounded shield substantially conforming inshape to the lower part of said envelope on the exterior' thereof and serving as a support for the same, said shield being provided with an aperture 1n line with the longitudinal axis of the tube for allowing useful X-rays to pass therethrough.

tar cathode being substantially circular in form and having an opening in the center of suicient size and disposed with respect to said anode in such manner as to permit a solid beam of X-rays to pass therethrough.

16. An X-ray device comprising an envelope, and X-ray emitting anode and a filamentary electron-emitting cathode therein, said cathode being-composed of at least one turnof wire and so arranged with respect to said anode as to permit a solid beam of X- rays to pass therethrough.

17. An X-ray device comprising `an envelope, an X-ray emitting anode and an electron-emitting cathode, said cathode com rising a plurality of turns of wire in the orm of a helix having an opening between the turns thereof through which a solid beam of X-rays is permitted to pass.

18. An X-ray device com rising an envelope, an X-ray emitting ano e anda filamentary electron-emitting cathode, the longitudinal axis of said anode and cathode being coincident, said cathode being substantially circular in form and having an openin of suiiicient size to permit a solid. beam o X- rays to pass/therethrough.

19. In an X-ray tube, an anti-cathode comprising a body of metal and a target of good X-ray emitting material in the end thereof, the end of the anticathode being rounded and the exposed surface of the target formmg a part of said rounded end.

In an X-ra tube, an anti-cathode comprlsing a body o metal and a target of good X-ray emitting material inset in the end thereof, the surface of said target being convex and merging with the surface of said body so as to form a continuous unbroken surface. 21. In an X-rajyitube, an electron-emittin cathode and an -ray emittiner anode saiil anode being lcomposed of a body of suitable target matorral embedded 111 11 second body of material of higher heat conductivity :1nd

sold second body having a form free from sharp angles, whereby the tendenc of said second body to soften in restricte parts is reduced.

22. An X-ray device comprising an envelope, means for generating X-rays including electrodes, means for absorbing undesirable portions of the X-rays and a grounded electro-conductive curved shield mechanically and conductively connected with one of said electrodes so as to be at the same potential thereof, said shield being fitted around and in close proximity to that portion of the envelope containing the electrode to which said shield is connected.

23. An X-ray device having a cooperating cathode and anode producing an ovoidal field, comprising an envelope shaped substantially as an ovoid, the major axis of which substantially coincides With the axis of the electrodes. i'

24. An X-ray device comprising an envelope, a thermionic cathode, a cooperating anticathode, and a substantially hemispherical shell-like focussing device, said focussing device being of large diameter and extending beyond the sides of said anti-cathode to such an extent as to prevent stray electron bombardment of the walls of the envelope.

25. An X-ray device comprising an envelope having a shape conforming substantially to the shape of the electrical field therein, an electron-emitting cathode, a target generating X-rays by cooperation with said electron-emitting cathode, which cathode encircles the useful X-rays generated and means for focusing the electron stream comprising an annular 'member between the target and the cathode.

In testimony whereof, I have hereunto subscribed my name June 7, 1921.

MONTFORD MORRISON.