US3081413A

US3081413A - X-ray tube with gas gettering means

Info

Publication number: US3081413A
Application number: US52007A
Authority: US
Inventors: Harold R Cummings
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1952-07-19
Filing date: 1960-08-22
Publication date: 1963-03-12
Anticipated expiration: 1980-03-12

Description

March 12, 1963 H. R. cuMMlNGs x-RAY TUBE WITH @As GETTERING MEANS Original Filed July 19. 1952 United States Patent O July 19, 1952. This application Aug. 22, 1960, Ser. No. 52,607

8 Claims. (Cl. 313-60) The present invention relates in general to electronics, and has more particular reference to 'electron flow devices of the sort comprising an anode and a cooperating cathode enclosed within a sealed envelope, whereby electrons emitted at the cathode may be caused to travel toward and impinge upon the anode, the invention relating specifically to an improved electron ow device of the sort mentioned and constituted for operation as an X-ray generator. This application is a continuation of my application Serial No. 299,851, -led July 19, 1952, which is now abandoned.

An important object of the present invention resides in providing improved and simplified gettering means particularly well suited for use in X-ray generating tubes; a further object being to employ metal zirconium as a getter.

Another important object is to provide a body of suitable gettering material in the anode structure of an electron ilow device, such as an X-ray tube, in close heat exchange relation with the electron receiving or target portions of the anode.

Another important object is to provide an electron flow device, such as an X-ray tube, having a rotating anode element providing an electron target member and carrying a body of gettering material immediately adjacent, behind and in heat exchange relation with said target member; a further object being to form the rotating anode as a turnable shaft of metal, such as tantalum, having low thermal conductivity and high melting temperature, and carrying an electron target forming disk thereon, and a ring-like body of gettering material on the shaft immediately adjacent and in heat exchange relation with said disk; a still further object being to employ gettering means comprising a ring-like washer of zirconium supported mechanically upon a thin disk of tantalum or similar material adapted to retain strength and shape under high temperature conditions.

Another important object is to provide improved means for mounting gettering material in heat exchange relation with respect to the rotating anode of an electron flow device, such as an X-ray tube, a further object being to provide, in an anode comprising a turnable shaft carrying an y electron target forming disk thereon, a ring-like support washer seated in a peripheral groove formed in the shaft adjacent the target forming disk, said washer carrying a ring-like body of metallic gettering material on the turnable shaft immediately adjacent and in heat exchange relation with the target forming disk, the ring-like body of gettering material and its supporting disk being formed with registering slits extending in a direction non-radially of the shaft, said slits extending preferably tangentially of said shaft to facilitate the application of said body of gettering material and its supporting washer in groove mounted position on the shaft.

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, discloses preferred embodiments of the invention. Referring to the drawings:

FIG. i1 is a sectional view taken through an electron ow device embodying the present invention;

n austin Patented Mar. 12, 1963 lCe FIG. 2 is an end view of the device shown in FIG. 1;

FIG. 3 is an enlarged sectional view taken substantially along the line 343 in FIG. l; and

FIGS. 4 and 5 are perspective views of parts shown in FIGS. 1 and 3;

To illustrate the invention the drawings show an electron flow device comprising an X-ray generating tube 111 embodying anode and cathode structures ,112 and 1.3 mounted in spaced apart relationship, in position to cooperate to cause the anode to function as a source of X-rays in response to impingement thereon of electrons emitted by the cathode structure. The anode and cathode structures are supported on and enclosed by a sealed and evacuated envelope 14, preferably comprising glass, the anode structure providing an electron target 19 in position to receive electrons emitted by electron emission means comprising a portion of the cathode structure.

X-ray generating tubes operate for the production of X-rays in response to the impingement at high velocity on the anode target of electrons produced by the excitation of the cathode, as by means of electrical energy supplied thereto, through a suitable power supply cable 67 having connection terminals 68. X-rays thus generated at the target may be directed thence as a useful beam '70 p'rojected outwardly of the enclosing envelope, as through a window 71 formed in the envelope. Electron impingement upon the target results in the generation of relatively large quantities of heat therein, such heat being dissipated through and outwardly' of the enclosing envelope. When in operation, the temperature of the target portion of the anode structure may be of the order of 1300 C., it being usual, in the interests of eiiiciency, to operate the genera- `move all gas from within the envelope, including' any gas that may be occluded in the anode and cathode structures and in the material of the envelope itself. Means may also be provided within the envelope for performing a gettering operation to absorb, and hence render inert and innocuous, any trace of gaseous matter which may remain in the envelope after evacuation, or which may be produced within the envelope during the operation of the device; and the present invention contempiates the provision of improved gettering means for electron flow devices, especially those adapted for the production of X-rays. i f

As shown, the envelope 14 may comprise a sleeve-like, preferably cylindrical section 1S sized to relatively closely enclose the anode structure 12, at one end of the envelope, a medial section` 16 of hollow, preferably cylindrical configuration joined integrally with the sleeve portion 15 at one end thereof, as at '1S-J, said medial portion having substantially greater sectional size than the portion 15 and being coaxial therewith, and a sleeve-like, generally cylindrical section 17 integrally joined and connected with the medial section 116 at the end thereof remote from the section 15, as at 17-J, said section 17 having a longitudinal axis eccentrically offset with respect to the common central axis of the sections 1'5 and 16. The section 17 is sized to relatively closely enclose the cathode structure 13.

The envelope 14 may be formed with

re-entrant mounting portions

15 and 17 at the opposite ends of the envelope, that is to say, at the ends of the sections 15' and 1'7, respectively, which are remote from the medial portion 16, the anode and

cathode structures

12 and 13 respectively being mounted on and sealingly connected with the re-entrant portions 15 and (17'.

The anode structure 12 comprises support means 18 forming a cylindrical mounting structure adapted for assembly within the envelope portion 15, the support means being mounted at one end upon the re-entrant envelope portion 15', and extending at its other end to the junction of the

envelope portions

15 and 16. The anode structure 12 also comprises electron target means 19, preferably turnably mounted on the support means 1S and carried thereby within the enlarged medial envelope portion 16 adjacent the junction thereof with the portion 15, said target means 19 comprising a preferably circular member having peripheral edge portions comprising an annular electron target, in position for rotary movement about the central axis of the

envelope portions

15 and 16, to thereby travel the annular target continuously in alignment with the axis of the offset envelope portion 17.

While the support means 18 may embody any suitable or convenient structure for turnably supporting the target means 19 within the envelope, it preferably comprises a metal stem 20, as of steel, sealingly secured as by welding the same on preferably cup-shaped metal mounting and sealing means 2,1, by means of which the stem is mounted on the re-entrant portion 15' in position extending in coaxial alignment with the axis of the

envelope portions

15 and 16. As shown, the mounting means 21 comprises a cylindrical metal shell 21 having an edge making an annular glass-to-metal seal 22 with the inner end of the re-entrant portion 15', the opposite end of the cylindrical shell 21' being sealed, as by brazing the same to the peripheral edges of a disk 23. The disk 23 may be formed with a central opening through which the stem 2t) extends, the stem and disk being sealingly secured, as by brazing the same together around the edges defining the central opening of the disk. The stem 2) thus has a portion extending within the re-entrant envelope portion 15 and hence exposed outwardly of the envelope, and a portion extending within the envelope in the envelope portion 15.

The shaft portion 26 carries suitable bearing means for turnably supporting the target means `-19 on the stern, said bearing means preferably comprising roller bearings 24 mounted in spaced relation on the stern portion 20'. To this end, the bearings 24 may each comprise inner race means secured on the stern portion Z0', and an outer race 25. The inner race means of one of said bearings may be clampingly secured against a shoulder 26 on the stem by means of a clamping nut 27 threaded on the stern portion 20' and a clamping sleeve 28. The inner race means of the other lbearing may be clampingly secured on the stem portion 21)' between clamping nuts 29 threaded thereon.

The outer race elements of the bearings may support a sleeve-like support member 30, of metal such as steel, turnably on the stem portion 20'.

The support member 30 in turn may carry a sleevelike sheath 31, of material such as copper, snugly embracing and surrounding the support member 30 and firmly secured thereto, as by rivets 32. The sheath 31 projects outwardly of the opposite ends of the support member 30 to provide a skirt 33 in position surrounding and enclosing the mounting means 211 and its glass-to-metal seal with the re-entrant portion 15', at one end of the support member 30. The projecting end of the sheath 31, remote from the skirt 33, may be fitted with a closure cap 34, of metal such as copper, sealed on the end of the sheath 31, as by Welding or brazing, to enclose the bearings 24 Within the turnable structure comprising the

members

30, 31 and 34. The closure cap 34 preferably carries a stub shaft 35, of metal such as tantalum, having low thermal conductivity and a relatively high melting temperature, the shaft having an end portion extending through a central opening in the cap 34.- and peened over or riveted, as at 36, upon the inner face of the cap to secure the stub shaft thereon in coaxial alignment with the stem 2t), the target member 19 being secured on the cap remote end 38 of the stub shaft,

said end 38 being preferably of reduced diameter. Since the shaft 35 comprises metal of low thermal conductivity, it serves to thermally insulate the turnable support structure 13 from the target means `19, thereby tending to prevent heat generated at the target means 19 from reaching the bearings 24 in the support structure.

rlfhe target member 19 may have any suitable form or construction, and may comprise any preferred target material. As shown, the member 19 comprises a rearwardly dished disk of tungsten, formed with a central opening for snugly receiving the end portion 33 of the stub shaft, which may be riveted or peened over upon the front face of the disk to hold the same securely on the end portion 38.

The present invention contemplates the provision of gettering means within the envelope 14, such gettering means comprising a body of zirconium, the same being well adapted for the absorption of gas, especially when the gettering material is at an elevated temperature. The present invention, accordingly, provides for the heating of the zirconium gettering means as the result of the operation of the X-ray generating tube. To that end, the gettering material is mounted in the anode structure in heat exchange relation with respect to the target member 119, whereby the gettering material may be highly heated through the heating of the target member as the result of electron impingement thereon during the operation of the device as an X-ray generator. As shown in the drawings, the gettering means may comprise a disk-like body or washer 39 of zirconium metal, suitably mounted on the tantalum shaft 35 behind the target member 19. Since zirconium tends to soften, and hence to lose its strength and shape, at the high temperatures which prevail at and adjacent the target member 19, during operation of the device for X-ray generating purposes, the zirconium washer may be secured, as by spot Welding it, upon a backing washer 4h of metal, such as tantalum, capable of retaining its strength and shape under the temperatures prevailing at the anode during the operation of the device.

The supporting washer 4t) may be secured in position in any preferred or convenient fashion. As shown, however, the shaft 35 is formed with a circumferential, outwardly opening groove 37 of width equal to the thickness of the washer 40, and the washers 39 and 46 are provided with aligned slits 41 and 41' extending from the central :washer openings to the peripheral edges of the washers, preferably in non-radial manner. The diameter of the central opening of the washer 39 is preferably larger than the diameter of the shaft 35, While the central yopening of the Washer 4h is sized to snugly fit the bottom of the groove 37. Accordingly, by bending the

stacked washers

39 and 40 to relatively offset the facing edges thereof at the slits 41 and 41', the washer 40, carrying the washer 39 securely fastened thereon, may be applied to the shaft 35 in the groove 37 by disposing one of the bent ends thereof in the groove 37, and thereafter advancing said end circumferentially in the groove 37, by turning the washer with respect to the stem 35, until the washer has been completely seated in the groove. Such arrangement is relatively inexpensive to make and assemble, and allows the washers 39 and y40 to be easily applied at any stage in the assembly of the `anode structure, vand also facilitates the removal and replacement of the

washers

39 and 40 at any time.

By virtue of the zirconium gettering washer 39 being spaced from the target 19 by the tantalum stem 35, a substantial part of the heat transferred from the target 19 to getter 39 is due to thermal radiation rather than thermal conduction, since tantalum is a metal of low thermal conductivity. In this way the getter may be heated to its optimum operating temperature rather than to an excessive temperature (and therefore ineiiicient operation); the latter situation is the case when additional thermal conduction is provided by a stem of higher thermal conductivity as, for example, molybdenum, which is commonly used in the art for this purpose.

In order to rotate the target member 19, the sleevelike member 31 comprises the rotor of a mot-or, the stator of which may comprise an annular electromagnetic structure mounted in position outwardly of and encircling the envelope extension 17. By energizing such stator from a suitable source of electrical power externally of the envelope, the rotor comprising the structure turnably mounted on the spindle portion Ztl', within the envelope, may be driven `at desired rotational speed by electromagnetic action between the rotor and stator through the material of the envelope extension 17.

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 or scope of the invention, or sacrificing any of its attendant advantages, the forms herein disclosed being preferred embodiments for the purpose'of illustrating the invention.

The invention is hereby claimed as follows:

1. An X-ray tube comprising: an anode target, a getter mounted in said tube and spaced from said anode target, and spacing means connected to said anode target and to said getter for spacing said getter from said anode target, said Aspacing means comprising material having lower thermal conductivity than molybdenum, whereby a substantial portion of the heat which heats said getter is derived from heat radiated from said anode target.

2. An X-ray tube as recited in claim 1 wherein said spacing means comprises material having a melting point higher than the melting point of said getter.

3. An X-ray tube comprising: a rotatable anode target, a zirconium getter, a tantalum mounting means, one

portion of which is secured to said rotatable anode target and -another portion of which is secured to said zirconium getter for spacing said getter from said anode target, whereby a substantial portion of the heat which heats said getter is due to heat radiated from said anode target.

4. An X-ray tube comprising: a rotatable anode target, a zirconium getter, a mounting means intermediate said anode target and said getter for maintaining said getter in spaced relation to said anode target, said mounting means comprising a material having lower thermal conductivity than molybdenum,

5. An X-ray tube as recited in claim 4 wherein said mounting means comprises material having a higher melting point than said zirconium getter.

6. An X-ray tube having a sealed envelope, anode and cathode electrodes mounted within the envelope, said anode electrode having a rotary portion providing a stem of tantalum turnably mounted within the envelope, an electron target on the stem, said stem being formed with an `outwardly 'opening circumferential groove adjacent said target, a mounting disk of tantalum secured in said groove, :and a ring-like body of gettering material secured on said tantalum disk outwardly of said tantalum stem.

7. An X-ray tube having a sealed envelope, anode and cathode electrodes mounted within the envelope, said anode electrode having a rotary portion comprising a tantalum stem turnably mounted within the envelope, an electron target plate on the stem, said stem being formed with an outwardly opening circumferential groove adjacent and behind said target plate, a ring-like washer having an inner edge secured in said groove, said washer having a severance slit therein extending from said inner edge to the peripheral edge thereof, and a body of zirconium gettering material secured on said washer outwardly of said stem, adjacent and spaced from said target plate.

8. An X-ray tube comprising: an anode target; a getter mounting means having one portion thereof physically connected to said anode target; a getter; said getter being physically secured to said mounting means in a region spaced from said one portion, whereby said getter is physically spaced from said anode target through the intermedi ary of said getter mounting means; said getter mounting means having lower thermal conductivity than molybdenum and a higher melting point than said getter, whereby a substantial portion of the heat from said anode target which heats said getter is due to thermal radiation.

References Cited in the tile of this patent UNITED STATES PATENTS 2,274,865 Machlett Mar. 3, 1942 2,430,800l v Atlee Nov. 11, 1947 2,438,181 Morehead et al Mar. 23, 1948 2,469,626 Beers May 10, 1949 2,477,110 Atlee et al. July 26, 1949 2,502,070 Atlee et al. Mar. 28, 1950

Claims

4. AN X-RAY TUBE COMPRISING: A ROTATABLE ANODE TARGET, A ZIRCONIUM GETTER, A MOUNTING MEANS INTERMEDIATE SAID ANODE TARGET AND SAID GETTER FOR MAINTAINING SAID GETTER IN SPACED RELATION TO SAID ANODE TARGET, SAID MOUNTING MEANS COMPRISING A MATERIAL HAVING LOWER THERMAL CONDUCTIVITY THAN MOLYBDENUM.