US2885582A

US2885582A - X-ray tube

Info

Publication number: US2885582A
Application number: US575908A
Authority: US
Inventors: Locklin S Bell
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1956-04-03
Filing date: 1956-04-03
Publication date: 1959-05-05
Anticipated expiration: 1976-05-05

Description

May 5, 1959 s. BELL X-RAY TUBE Filed April 5, 1956 L a m m E S V m W K Na 0 O j Y B m. R m 2 iv ATTORNE United X-RAY TUBE Application April 3, 1956, Serial No. 575,908

3 Claims. (Cl. 313-55) The present invention relates in general to electronics and has more particular reference to the production of X-rays, the invention pertaining especially to an improved X-ray generating tube.

X-ray generating tubes commonly comprise an electron emitting cathode, a cooperating anode forming an electron target, evacuated envelope means hermetically enclosing the anode and cathode, and supporting the same in spaced facing relationship. The envelop of an X-ray tube usually embodies portions of electrical insulating material, such as glass, disposed in position to mount the cathode in the envelope and to relatively insulate the anode and cathode, in order that electrical pressure, at substantial voltage, may be applied therebetween to drive cathode emitted electrons toward and cause the same to impinge upon the electron targetprovided at the anode for the generation of X-rays. Rays thus produced at the target may be emitted thence outwardly of the envelope, for any useful purpose, through a suitable ray transmitting window formed in the envelope adjacent the ray generating target.

An important object of the present invention is to provide for enclosing the cathode mounting end portions of an X-ray tube in a suitable, preferably grounded casing adapted to be filled with oil or other suitable insulating material, and to dispose a high voltage cable receptacle in such casing in position with an end of the receptacle extending within a re-entrant portion of the cathode carrying and insulating end portions of the tube envelope, whereby thus to reduce the overall dimension of the tube and receptacle; a further object being to provide a diaphragm member comprising a length of flexible rubber tubing within the casing, whereby to compensate for changes in volume of the insulating material with temperature, said length of rubber tubing having one end closed and the other end vented to atmosphere outwardly of the casing.

Briefly stated, the objects of the present invention may be realized through the provision of an X-ray generatingtube having an anode forming a target surface facing an electron emitting cathode element. The anode may form one end of an hermetic envelope enclosing the cathode, and formed at the anode remote end of the envelope with a re-entrant envelope portion comprising insulating material, such as glass, and disposed in position to support the cathode structure in the envelope in coaxial alinement with respect to the anode. A casing may be secured on the envelope in position enclosing the glass cathode carrying portions thereof, the casing being adapted to contain a fluid insulating medium in position to submerge the cathode carrying envelope portion together with a high voltage cable receptacle carried in the casing in position extending within a re-entrant portion of the cathode mounting portion of thetube envelope, a length of flexible tubin'g clo sed at one end and in open communication with circumambient atmosphere outwardly of the casing, being enclosed within the casing and subatnt merged in the fluid insulating medium to compensate for expansion and contraction thereof.

The foregoing and numerous other important objects, advantages and inherent functions of the invention will become apparent as the same is more fully understood from the following description, which, taken in connection with the accompanying drawings, disclosed a preferred embodiment of the invention.

Referring to the drawings:

Fig. 1 is a sectional view taken longitudinally through an X-ray generating tube embodying the present invention; and

Fig. 2 is a sectional view taken substantially along the line 22 in Fig. l.

To illustrate the invention, the drawings show an X-ray generator 11 comprising an anode 13, forming anelectron target surface, a cathode structure 15 embodying an elongated electron emission element and envelope means 17 enclosing the anode and cathode. In accordance with the present invention, the anode 13 may comprise a sleeve-like, preferably cylindrical element, the cathode being supported concentrically within the anode and adapted for electron emission in all directions radially of the longitudinal axis thereof toward the inwardly facing surfaces of the surrounding sleeve-like anode element. The arrangement results in the generation of X-rays in all portions of the cathode encircling target surface of the anode, thereby producing large amounts of radiation at relatively low electrical current density at the target surface, thereby minimizing heat generation at the anode. The resulting radiation may be emitted at an end of the anode as a high intensity X-ray beam.

The envelope means 17 preferably comprises a plate or disc of steel 19, forming a frame having a central opening 21. A preferably cylindrical sleeve 23 of metal, such as, steel, is sealingly secured, at one end, to the plate 19, in position extending outwardly of the plate, on one side thereof, in coaxially alined communication with the opening 21, the anode being sealingly secured, at one end thereof, on and to the plate remote end of the sleeve 23, as by welding or brazing the parts together, the other end of the anode elementbeing closed by and carrying an X-ray transmitting window pane 27 forming a ray emitting Window in the envelope at the sleeve remote end of the anode element.

The side of the plate 19, remote from the sleeve 23, maybe formed with a shoulder 29 providing a circular seat, concentric with respect to the opening 21, for receiving one end of a mounting sleeve 31, which end may be welded or otherwise sealingly secured to the plate 19 at the shoulder 29. The sleeve preferably comprises steel containingappreciable quantities of nickel and providing a rim, remote from the seat 29 and adapted to form a seal 33 with a preferably glass cathode carrying envelope portion 35. The end of the said envelope portion 35, remote from the seal 33, preferably forms a reentrant sleeve portion 37 having an edge forming a glassto-metal seal 39 with the rim of a metallic end seal structure comprising a plate 41 and a mounting sleeve 43 sealingly secured, as by welding at one end, to the plate 41, said sleeve, at its other end, forming the glass-to-metal seal 39 with the terminal edge of the re-entrant sleeve portion 37.

The cathode structure 15 may comprise a body of metal, such as copper, forming a head 45 secured in and electrically connected with an end of a preferably copper sleeve 47. The other end of the sleeve may be secured on and electrically connected with a preferably copper collar 49 having a central opening, said collar 49 in turn being mechanically and electrically connected with one end of a tubular support 51. The other end of the support may be mechanically and electrically secured upon the plate 41 in coaxial alinement with a central opening 53 formed therethrough, said cathode structure being thus carried in position presenting the head 45 at the sleeve mounted end of the anode element.

An electron emitting element, preferably comprising a helical filament 57, is supported upon the head 45 in position extending coaxially within the cylindrical anode element. One end of the helical filament may be electrically connected with a conductor rod 59 supported on and electrically insulated from the head 45. The conductor rod may be electrically connected, as by means of a flexible conductor element 61, with a conducting stem 63 which extends coaxially within the collar 49, the tubular support 51 and the opening 53 of the mounting plate 41, and outwardly of said plate through a suitable envelope seal 65 into the space within the re-entrant sleeve portion 37 of the envelope. The other end of the helical electron emission filament 57 may be electrically connected with one end of an electrical conducting rod 67 which extends concentrically within the filament, the other end of said rod being mechanically and electrically secured upon the head 45. The stem 67 may also carry a metallic button 69 thereon at and outwardly of the stem connected end of the filament 57, said button extending between the filament and the overlying ray transmitting window pane 27, to thereby screen said pane from filament emitted electrons.

It will be seen from the foregoing that one end of the filament 57 is electrically connected, through the cathode structure, with the mounting plate 41, one side of which is exposed in the space within the re-entrant sleeve portion 37 of the envelope, the other end of the filament being connected with the stem 63 which has an end extending within said space. The filament 57, accordingly, may be excited for electron emission by a source of filament energizing power disposed outwardly of the envelope, by connecting said source with the mounting plate 41 and the stem 63. This may be conveniently accomplished by means of a suitable source connected cable and a cable connection receptacle 79 having cable'engaging contacts adapted to be electrically connected with the plate 41 and stem 63 within the re-entrant sleeve portion 37 of the envelope. To these ends, the glass envelope portions 35 and the mounting sleeve 31 may be enclosed within a preferably cylindrical metal casing 71 having a flanged end 73 adapted to be bolted, or otherwise detachably secured, upon the plate 19 outwardly of the mounting sleeve 31, suitable gasket means 75 being provided for sealing the flanged end of the casing 71 to the plate 19. The opposite end of the casing 71 may be fitted with a collar or gland 77 sealingly secured in any suitable or preferred fashion in the end of the casing. The gland 77 may form a seat defining a central opening through which the cable receptacle 79 may extend into the casing, means being provided for detachably securing the receptacle in the casing as by clamping a shouldered portion 81 of the receptacle upon the seat formed on said gland, a suitable sealing gasket 83 being provided to seal the receptacle in said gland.

The receptacle may be of any suitable, preferred or conventional construction providing terminal studs 84 at its inner or gland remote end, in position to be electrically connected, the one with the plate 41, as by means of a connecting terminal 85 on said plate, and the other with the exposed end of the conducting stem 63, said studs being electrically connected with contacts disposed in position within the receptacle for electrical connection with the corresponding terminals of the end structure of a conventional power supply cable.

The casing 71 is adapted to contain oil or other insulating substance in which the receptacle 79, as well as the

envelope portions

31 and 35, and the electrical connections between the receptacle studs and conductors, 63

and are immersed. In order to compensate for variations in volume of the insulating medium in the casing 71, in response to changes in the temperature thereof, a diaphragm device 87 may be provided immediately adjacent the gland 77. The diaphragm device may comprise a length of flexible tubing of rubber-like material that is resistant to deterioration when in contact with the insulating medium in the casing 71. The length of flex ible tubing may be disposed in position encircling the re= ceptacle 79 adjacent the gland 77, said tubing being sealingly closed at one end by any suitable sealing means, the other end of the diaphragm tube being connected to atmosphere outwardly of the casing, as through an elbow fitting 89 and an opening 91 formed on and in the gland 77 The anode element 13 preferably comprises a sleevelike, preferably cylindrical body of heat conducting metal, such as copper, having a layer of suitable electron tar get material coated or otherwise applied upon the inwardly facing surfaces of the cylindrical body, in order to provide an inwardly facing electron target surface. At its outer or Window carrying end, the anode element 13 may be formed with a peripheral window carrying rib 92 concentric with and of greater diameter than the inner face of the target layer 90. The window structure may comprise the outwardly bowed pane element 27, preferably of beryllium or other material highly translucent to X-rays, and a pane mounting frame 94 of Monel metal, cold rolled steel or other metal capable of being readily sealed to the edges of the pane element 27, as by brazing with a' copper-silver alloy. The frame 94 may be formed with an integral flange adapted to be sealingly secured on the rib 92, as by brazing. It will be seen that the rib 92, the frame element 94 and the peripheral frame sealed edges of the pane 27 may all be disposed outwardly of the ray generating anode target layer 90 and hencewill not be in the path of the useful X-ray beam emitted through the window.

The anode element may also be provided with preferably integral, radially outwardly extending heat dissipating fins 93 at the outwardly facing surfaces of the sleevelike body; and means may be provided for continuously circulating a fluid cooling medium, such as water, in heat exchange relation with respect'to the fins 93 during the operation of the X-ray generator. To this end, a jacket sleeve 95 may be sealed, at one end, to the plate 19, as by welding or brazing the end of the jacket sleeve to the plate, in position concentrically enclosing the sleeve portion 23 of the envelope. The end of the jacket sleeve 95, remote from the plate 19, may be disposed opposite the medial portions of the target member 13 and may be sized to snugly enclose and engage the outer edges of the heat dissipating fins 93.

The outer end portions of the anode member 13 may be enclosed by a hollow ring-like shell 97 of metal forming a circumferential chamber in communication with all of the spaces defined between the fins 93. One end of the shell 97 may be peripherally sealed to the anode embracing end of the jacket sleeve 95. The other end of the seal 97 may be peripherally sealed upon the anode element 13, as at the window frame element 94, in position enclosing the spaces defined between the fins 93 outwardly of the anode enclosing end of the jacket sleeve 95. A cooling fluid from any suitable source may be delivered, as through a conduit pipe 99, into the circumferential space defined by the shell 97, and may flow thence in the spaces defined between the radial fins 93, in heat exchange relationship with respect to said fins, and then through the cylindrical space defined within the jacket sleeve 95 and outwardly of the sleeve portion 23 of the envelope. The cooling fluid may thus absorb heat from the anode member 13 and the sleeve portion 23 of the envelope, and may be discharged from within the jacket sleeve 95 through an oil outlet conduit 101 connected with the jacket sleeve I adjacent the plate 19.

It will be seen from the foregoing that the outwardly dished or bowed window pane 27 improves window strength and reduces window pane thickness required to resist atmospheric pressure. The shape of the window pane also provides adequate clearance for the cathode structure, permitting the filament to be supported in position adjacent the Windowed end of the anode.

The electron target area of the sleeve-like anode is large as compared with the target area of conventional tubes, thereby permitting relatively large ray generating current flow in the anode at relatively low current density. The electron target surface is disposed closely adjacent the Window pane 27, thereby allowing an X-ray exposure object to be disposed closely adjacent the ray source. It will be noted that the diameter of the cylindrical target area is substantially less than the diameter of the Window pane 27, to aid in obtaining short target-irradiation object distance, and also to assure against radition cutofl by the window edge seal or by the window frame member at the marginal edge of the pane.

The disc 69, at the end of the filament, not only assists in focusing electrons upon the desired target area, but also serves to protect the window pane from stray electron impact. The shape of the cathode structure, particularly the enlargement afforded by the head, sleeve and collar 45, 47 and 49, in conjunction with the restricted opening 21 comprising the waist portion of the envelope between the anode and the cathode supporting and insulating portions 35 of the envelope, serves to screen said glass envelope portions from deleterious bombardment by electrons during the operation of the device as an X-ray generator.

The tube is designed for operation with the anode connected to ground and cooled by a fluid medium, such as water. The arrangements for circulating the cooling fluid are preferably such that, when the device is in operation with the ray emitting window facing downwardly, the cooling fluid is required to travel upwardly along and in close contact with the finned portions of the anode.

The cathode supporting end of the envelope is enclosed in a grounded metal casing filled with a suitable insulating medium, the casing containing and supporting a cable plug receptacle having an end partially extending within the re-entrant portion of the tube envelope, whereby to reduce the overall length of the device.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit and scope of the invention, or sacrificing any of its atendant advantages, the forms herein disclosed being a preferred embodiment for the the invention.

The invention is hereby claimed as follows:

1. An X-ray generator comprising an anode of sleevelike configuration providing a circumferentially disposed inwardly facing target surface, an electron emission element disposed within said anode in position to emit electrons for ray generating impingement upon said circumferentially disposed target surface, and a sealed envelope enclosing said emission element and target surface, said envelope comprising a sleeve structure embodying said anode, at one end thereof, and a re-entrant envelope portion at the anode remote end of said structure, cathode means mounted on said re-entrant envelope portion and extending thence in said sleeve structure to support the emission element within said anode, a casing secured on said envelope in position enclosing said re-entrant portion, said casing being adapted to contain a fluid insulating medium in position to submerge the anode remote end portons of said envelope, including said re-entrant portions, in said insulating fluid, and a length of flexible tubing enclosed in said casing to compensate for expansion and contraction of the insulating medium, said length of tubing being sealingly closed at one end and in open communication with circumambient atmosphere outwardly of said casing.

2. An X-ray generator comprising an anode, a cooperating cathode, and a sealed envelope enclosing said anode and cathode, said envelope comprising a glass cathode carrying portion at an end thereof, a casing secured on said envelope in position enclosing said glass cathode carrying portion and adapted to contain a fluid insulating medium in position to submerge said cathode carrying envelope portion in said fluid, and a length of flexible tubing enclosed in said casing to compensate for expansion and contraction of the insulating medium, said length of tubing being sealingly closed at one end and being in open communication with circumambient atmosphere outwardly of said casing.

3. An X-ray generator as set forth in claim 2, wherein the cathode carrying portion is formed with a re-entrant end forming a chamber, and a cable receptacle is mounted on the casing in position extending within said chamber and submerged in said fluid insulating medium.

purpose of illustrating References Cited in the file of this patent UNITED STATES PATENTS 1,624,451 Weinhart Apr. 12, 1927 2,148,000 Verhoefi Feb. 21, 1939 2,346,929 Litton Apr. 18, 1944 2,472,745 Frevel June 7, 1949