US2345723A - X-ray tube - Google Patents

Description

API', 1944- z. J. ATLEE ETAL v 2,345,723

X-RAY TUBE Filed Aug. 17, 1942 INVENTORSM m@ @YQ/A mgm IIL.

@w mwgw@ www5@ QN mw @a @Q1 Sgm@ Patented Apr'. 4, 1944Y X-,nAv 'runs Zed J. Atlee, Elmhurst, and James C. Fiimer, Wheaton, Ill., assignors to General Electric X-Ray Corporation, Chicago, Ill., a corporation of New York Application august i7, i942, serial No. #l-aree (ci. 25e- 1428 2 Claims.

My invention relates in general to electronics and has more particular reference to an X-ray generator of improved construction and particularly well adapted for use in crystallography.

An important object of the present invention resides in providing an X-ray generator having an all metal envelope structure substantially immune to deterioration through X-ray and electrcstatic action thereon, thereby providing a generator particularly adapted for X-ray diffraction analysis where it is desired to obtain diffraction patterns at high speed with generator loadings of the order of one hundred milliarnperes at twenty-live kv. p. on a one millimeter target spot;

a further object being to provide a generator of f the character mentioned having a rotating anode whereby safely te accomplish loadings of the order mentioned without endangering the target.

Another important object is to form the envelope of the generator of tubular metallic stock having an electrode sealed within the envelope at one end thereof by means of a glass sealing member on which the electrode is supported, and to form the electrode to protect the glass seal against electron impingment.

Another important object is to provide a generator having a sealed metallic envelope containing opposed anode and cathode electrodes in facing relationship within and supported in the opposite ends of the envelope, one of the electrodes only being supported and sealed in place on a glass seal member forming a part of the envelope at one end thereof, the other end being supported on and electrically connected to the envelope.

A still further important object is to provide an envelope structure for an X-ray generator utilizing metallic material for the envelope zones exposed to the deleterious effects of X-rays and electronic action, and to provide means allowing for the egress of X-rays from the generator through the metallic envelope walls without appreciable absorption of the rays by the envelope material.

A further object is to provide an X-ray tube or generator for crystallography and adapted for high voltage operation whereby to allow X-ray diifraction patterns to be obtained at relatively high speed, the diiraction generator having an envelope comprising tubular metallic sleeve means enclosing a rotating anode in one end of the envelope, and an opposed cooperating cathode supported in the opposite end of the envelope; a further object being to support the rotating anode in suitable bearing means mounted on a stem sealed in, xed upon and electrically connected with the metallic envelope.

A further object is to provide for lubricating the bearings of the rotating anode by vaporizing and applying a suitable metallic lubricating medium upon the bearings from time to time during the service life of the generator.

Another important object is to provide for circulating a cooling uid, such as oil or water, directly upon and in Contact with the envelope portions which contain the anode.

Still another important object is to form the anode with an elongated skirt embracing the anode bearings and the stem carryingr the same, and to provide the skirt with black body coating both Within and outside of said skirt, in order to obtain maximum heat radiation from the anode skirt to cool the anode.

A further important object is to provide an X-ray generator of the character mentioned embodying a cathode and a rotating anode enclosed within a sleevelike metal envelope, and to provide for turning the anode by means of a motor mounted outwardly of the envelope in position to exert a magnetomotive turning force upon the anode through the metallic envelope walls; a further object being to utilize pole pieces set in the metallic walls of the envelope in a fashion magnetically insulated from the metallic walls, said pole pieces being mounted opposite the anode to deliver driving torque thereto through the pole pieces when the externally mounted motor is electrically energized.

Among the other important objects of the invention is to provide an unusually inexpensive yet rugged X-ray generator construction adapted for manufacture by mass production methods and embodying a substantially all metal construction, having the manufacturing advantages inherent in metal parts produced by machine tools, together with the low cost afforded by constructing the envelope from standard seamless metal tubing.

These and numerous other important objects,

r advantages, and inherent functions of the invention will be fully understood from the following description, which, taken in connection with the accompanying drawing, discloses a preferred embodiment of the invention.

Referring to the drawing:

Figure l is a longitudinal section taken through an X-ray tube structure embodying the present invention;

Figure 2 is a sectional view taken substantially along the line 2 2 in Figure l; and l Figure 3 is a fragmentary perspective view of a part of the anode mounting stem forming a part of the device shown in Figure 1.

To illustrate our invention, we have shown in the drawing an X-ray generator II comprising an anode structure I2 embodying a target face i3, a cathode structure I4 embodying an electron source comprising a filament I5, and an envelope structure I6 enclosing the anode and cathode.

The generator illustrated is particularly well adapted for crystallography, that is to say, the examination of materials by observation of the diffraction characteristics thereof when exposed to X-rays. Such analysis of materials may be accomplishedV by exposing the same to X-rays and recording the X-ray diiraction characteristics of the material being examined, as by photographing the same upon sensitized film.

X-rays, of course, are generated at the target I3 by impingement thereon of electrons emitted by the filament I5, and the radiation from an X- ray generator consists of a continuous or white spectrum, the wave length and intensitydistribution of which depends largely upon the electrical potentials at which the generator is'operated. Each target material also imparts its own individual spectral characteristics in rays produced thereby, and each spectrum comprises a relatively few lines, each having a specic wave length which depends only on the type of target material employed. The X-ray spectra of the various target materials are entirely independent of operating potential of the generator above a minimum voltage which minimum voltage also is characteristic of the target material. Any suitable target material may, of course, be employed for X-ray diffraction analysis, provided that the material of the target, and hence its line spectr'um be known, otherwise, the spectral lines caused by the target material in the spectrograph of a sample being examined may be mistaken for lines supposedly caused by the test sample.

Electrons are emitted by the filament when the same is electrically energized, as by the iiow of electrical current therethrough under the influence of electrical potential applied at the opposite ends of the filament; and electrons emitted by the filament are caused to impinge upon the target I3 under the inuence of electrical potential applied between the anode and the lament of the cathode.

The target I3 may comprise any preferred target material, such as tungsten, molybdenum, copper, nickel, cobalt, iron, chromium or other desired target material. 'Ihe choice of a suitable target material for X-ray diffraction analysis depends upon the type of specimen to be eX- amined, the particular technique employed and the sort of information sought, the X-ray spectrum of the rays produced by a generator depending upon the type of target material employed in producing the rays.

Since the spectra of target materials do not vary with the operating potential of the generator, it is desirable, in the interests of speedy diffraction analysis, to provide a heavy duty generator and to operate the generator under a heavy load; and our present invention resides in the provision of a practical, heavy duty generator for X-ray diffraction analysis adapted for operation under a load of the order of one hundred milliamperes and twenty-live kv. p. on al focal spot one millimeter wide. Obviously sucha loading generates destructive quantities of heat at the target, and in order to accommodate the same,

we have provided a tube structure embodying a rotating anode and facilities for rapidly removing from the anode such heat as may be applied thereto during the operation of the generator under heavy load.

We also employ an inexpensive generator envelope structure preferably comprising seamless metal tubing, in which the anode and cathode of the generator are enclosed and supported in operating position, the metal envelope structure being substantially immune to the action of electronic impingement and electrostatic effects, to which the envelope is subjected when operating at the relatively high voltage for which the generator of our present invention is designed.

As shown in the drawing, the envelope I6 preferably comprises a Seamless steel tube I7, of size to receive the anode snugly therein, while permitting the anode to turn freely within the tube Il. The envelope also comprises a cathode receiving portion I B comprising a seamless steel tube, preferably of somewhat larger diametral size than the anode receiving portion Il of the envelope. The envelope portions I1 and I8 may be sealed together at their abutting ends by a joining ring I9, to which the abutting ends of the tubes I1 and i8 are welded or otherwise sealingly secured in grooves formed in the ring i9. The tubes extend, respectively, on opposite sides of the ring to provide an integral tubular envelope having an elongated anode enclosing portion Il which is preferably of smaller diametral dimension than the preferably somewhat shorter cathode receiving envelope portion I3.

The anode i2 preferably comprises a head 2i! of copper or other suitable target material providing an annular target surface I3; and for the purposes of diffraction analysis, itis desirable that the anode head 29 be composed of essentially pure target material for the reasons stated in the co-pending application of Zed J. Atlee for X-ray tube, Serial No. 440,516, iiled April 25, 1942, upon which United States Letters Patent No. 2,329,320, issued September 14, 1943; and, of course, the means for and method of providing a target surface of pure target material, as taught in said co-pending application, may be incorporated in the device herein described.

The head 20 is secured in the end of a sleevelike anode skirt 2i, which preferably comprises a cylindrical copper tube in which the head is secured in any suitable fashion, as by brazing,

" in order to provide for the rapid transfer of heat from the head to the' skirt.

Means is provided for attaching the anode upon a rotating carrier frame 22, as by fastening the frame within the skirt and immediately behind the head Z by means of fastening screws 23. The carrier frame, in turn, is secured on the head 24 at one end of a spindle 25 carrying spaced apart roller bearings 26. These roller bearings are secured in spaced position on the spindle by means of a spacing tube 27 and clamp nuts 29 which hold the inner races of the roller bearings 25 upon the stem 25 in spaced position thereon. The outer races of the bearings 26 are clampingly secured in spaced relationship in a cavity 30 formed in a mounting stem 3i by means of a spacing tube 32 extending within the cavity between the outer races of the bearings, and a clamp gland 33 tted and secured in the stem 3i at the open end of the cavity 39. The stem 3|, near its end remote from the open end of the cavity 39, is provided with a shoulder 34 for receiving a metal sealing disc 35, which is sealed on the stem 3l at the shoulder 34, as by brazing or welding,

The anode, having rst been mounted and assembled on the stem to provide an assembly unit, may then be mounted in operating position in the envelope simply by sealing the peripheral edges of the disc 35 in the open end or the envelope portion Vl. The disc 35 is preferably formed with a groove for receiving the end of the envelope portion il whereby to align the anode assembly unit in position in the envelope. When mounted, the head 2t of the anode projects into the end of 'the envelope portion i8 adjacent the connecting ring i9. The cathode i4 comprises a plate-like head 35 formed with a pocket 37 in which the electron emitting filament l5 is mounted in position to emit electrons in the direction of the target S3 when the device is in operation. The filament, at its opposed ends, is mounted on, electrically connected to and supported by conductor stems which extend through openings in the head it and which are mounted in insulated brackets behind the head. The iliament supporting stems are electrically connected with conductors 3S which pass through openings in a metallic mounting disc or plate 39 forming a part of the cathode structure. These openings are suitably sealed around the conductors 38 as by means of glass beads hermetically sealing the openings and insulating the conductors from the metal mounting plate S9. The cathode head 36 is supported on the mounting disc 39 by means of a tubular metal skirt lill.

Suitable means for mounting the cathode structure in the envelope portion i3 is provided. To this end, the mounting plate 39 is provided with a marginal groove and an annular sealing member 4l, comprising metal having a relatively high proportion of nickel, is sealed on said mounting plate 39 in said groove. The other end of the member il is formed with a tapered annular edge which makes a glass-to-inetal seal with one end of a glass sleeve 43, the cathode skirt All being extended and having marginal portions enclosing the glass sleeve 43, including the annular glass-to-metal seal and the sealing member 4l. The other end of the glass sleeve 43 forms a glassto-metal seal #lo with the tapered annular edge of another seal ring 45. The ring 45 comprises metal having a relatively high proportion of nickel, and is brazed, soldered or otherwise sealed in a mounting collar lll. This collar 4'! has an annular groove sized to snugly receive the end of the envelope portion 58. The cathode structure, having rst been assembled on its mounting .Y

sleeve 43, including the seal member 45 and the collar l'l as an assembly unit, the cathode may be assembled in operating position in the envelope merely by applying the collar 4'! to the end of the envelope portion i3 and sealing the same in place, as by brazing or soldering From the foregoing it will be seen that the envelope may be fabricated at minimum cost from standard tubular stock. The anode and cathode, including their respective mountings, may be constructed as subeassembly units. Thereafter the tube may be built merely by applying the anode and cathode structures in the opposite ends of envelope, evacuating the same and soldering the discs 255 and :il in the opposite ends of the envelope. The evacuation and soldering may be accomplished by brazing the assembled device in a vacuum chamber in order to evacuate the envelope, and after the same has been exhausted to a desired degree, the sealing of the disc 35 and of the collar 4l in the opposite ends of the envelope may be accomplished by induction heating means while the device remains in the vacuum chamber. Of course, the envelope may be assembled and sealed up prior to evacuation, in which case the sealed envelope may be connected with an exhaust pump by a connection formed in the glass cathode mount 43, which connection may be sealed olf, as at 48, after the envelope has been exhausted by the pump to a desired extent.

We prefer also to provide means in the anode sub-assembly for lubricating the bearings 26. To this end, we provide openings 4S forming chambers in the walls of the Stem 3l, each chamber being in open communication with one of the roller bearings 2. In each chamber 49 we dispose carrier means for a suitable lubricating medium, such as barium. In the illustrated embodiment the carrier means comprises a loop of hollow wire 5t containing the lubricating medium and having a weakened wall portion facing the bearing to be lubricated. The wire loop at one end is electrically connected, as at 5l, on the Stem 3| at one end of the opening 49. The other end of the loop is electrically connected to an insulated conductor 52 which extends preferably in a longitudinal groove 53 formed in the stein 3l and extending from the opening 4B to a point adjacent the seal disc 35. Each conductor adjacent said seal disc, is electrically connected, asat 54, with a corresponding conductor E5 extending through openings in the disc 35. Each conductor 55 extends through an opening which is hermetically sealed around the conductor, as oy a glass bead, to thereby insulate the conductors 55 from the metal sealing disc.

By applying electrical potential between the conductors 55 and the stem 3l outwardly of the envelope H, the lubricating medium contained in the hollow wire forming the loops 5t may be electrically heated and vaporized. The lubricating medium so vaporized will escape through the weakened wall portion of the loop and will bie projected upon the working surfaces of the bearings 26 to thereby dispose a nlm of inert metallic lubricating medium on the working surfaces of such bearings.

It will be understood, of course, that when an X-ray generator is in operation, X-rays are generated at the target I3 as a result of impingement thereon of electrons emitted by the cathode I5. Such electronic impingement results in the generation oi relatively large quantities of heat at the target surface, and this heat is dissipated through the body of the anode, including the anode skirt 2l, and into the interior oi the casing, escaping eventually through the walls of the envelope. During the operation of the generator. as such, the anode l2 is desirably rotated in order to minimize the danger of overheating and burning the target itself. Rotation of the anode is preferably accomplished by induction motor means, including a stator 55 mounted around the envelope portion I'.' opposite the anode which acts as a rotor in conjunction with the stator 55. Since the sleeve l? preferably comprises a steel tube, we provide for developing torque in the anode sleeve by inserting preferably four stationary pole pieces 5T in suitable openings formed in the sleeve ll, said openings being sealed around the pole pieces to preserve the vacuumtight condition of the envelope. The pole pieces 51 preferably comprise plugs of iron or other magnetic material, and if desired, may be magmeans of copper collars.

To aid in the rapid dissipation of heat from the head 2&1, we apply a black body coating upon the internal and external surfaces of the anode skirt 2 I, in order to increase radiation from the anode skirt as much as possible. We also apply a black body coating upon the interior of the envelope portion I1, in order to provide maximum heat absorption, it being understood that a black body at relatively high temperature radiates heat rapidly, while a black body at a low temperature absorbs heat rapidly.

In order to further improve the heat dissipating characteristics of the generator, we provide `for jacketing the envelope portions il and 35 for the circulation therearound of a cooling fluid, such as water. To this end, the envelope portion I1, adjacent the pole pieces i, is provided with an outwardly extending ange 53 to which may be fastened, as by screws, a collar 59 secured to one end of a jacketing sleeve 6b which encircles the envelope portion II and which has an end 6I extending beyond the anode support disc 35, said end 6I of the jacket being closed by an end plate S2. The jacket means may be additionally secured upon the envelope of the generator by means of a screw 63 in the end plate B2, said screw threading into the projecting end of the anode support stem 3i. A pipe or conduit 64, extending through and sealed in the end plate 62, may be provided for delivering a cooling fluid into the jacket adjacent the collar 59, the cooling uid passing thence through the jacket and around the enclosed envelope portion I1, the disc 35 and the projecting end of the anode stem 3I, and escaping from the jacket through an outlet conduit 65 formed in the end plate 62. It will be noted that the jacket, being of metal and being electrically connected with the tube I'I and with the anode stern 3|, is grounded and forms an electrical connection with the anode itself. Cathode energizing potential may be applied between the conductors 38, while generator operating potential may be applied between one of the conductors 38 and any convenient part of the metal envelope.

The steel envelope is preferably formed with a window opening 5B opposite the target I 3, said opening being preferably formed in the envelope portion I8. A pane of material El which is substantially transparent to X-rays is sealed on the envelope at said opening, and we prefer to utilize beryllium as a window pane material, since beryllium has an extremely low X-ray absorbing characteristic. The beryllium pane may be applied by soldering it in a ring 68 of Monel metal or other metal containing a relatively large propor tion of nickel, the beryllium pane being soldered in the ring 6B by means of a brazing alloy which may comprise equal parts of silver and copper. The soldering or brazing operation may be accomplished in a hydrogen furnace with calcium chloride or other halogen solder as a flux. The copper-silver alloy has the property of wetting the beryllium, but does not go fully into solution therewith before a satisfactory hermetic joint is formed, so that the beryllium window pane remains substantially uncontaminated by copper or silver in solid solution therein after the soldering operation. The ring 68 may be sealed upon the envelope sleeve I8 by means of an eutectic alloy netically insulated from the steel envelope by of silver and copper comprising substantially ,seventy-two percent silver and twenty-eight percent copper, which affords a satisfactory solder kfor joining the nickel alloy ring 68 with the steel tube I B,

Substantially all of the parts of the generator herein illustrated and described are metal parts and consequently can be fabricated to precise size. The only non-metal portions of the generator are the mounting sleeve i3 and the preferably glass seals through which the conductors 38 and 55 extend in the plates 35 and 39. The substantially all metal structure thus affords considerable manufacturing economy, both in the fabrication of parts and in the assembly operations. The herein disclosed construction, furthermore, results in the provision of an extremely sturdy and serviceable X-ray generator, in which the facilities for cooling the anode permit operation of the generator under relatively heavy load for the production of intense X-ray spectrographs, by means of which diffraction analysis may be accomplished with great rapidity.

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 form herein disclosed being a preferred embodiment for the purpose cf illustrating the invention.

The invention is hereby claimed as follows:

l. A device of the class described comprising a tubular metallic envelope, opposed electrodes comprising an anode and cathode supported within said envelope, said anode being electrically connected with said envelope at an end thereof and rotatable in relation to said envelope and said cathode being supported on and insulated from said envelope at the other end thereof, said envelope comprising a tubular anode enclosing portion closely embracing said anode while permitting rotation thereof, said envelope including a cathode enclosing portion of sectional dimension larger than that of the anode enclosing portion, said anode and cathode enclosing portions comprising metallic tube sections in co-axia1 alignment and havingV abutting ends mutually sealed upon a connecting ring, and pole pieces sealed in openings formed in the anode enclosing portion adjacent said ring.

2. A device of the class described comprising a tubular metallic envelope, opposed electrodes comprising an anode and cathode supported -within said envelope, said anode being electrically connected with said envelope at an end thereof and rotatable in relation to said envelope and said cathode being supported on and insulated from said envelope at the other end thereof, said envelope comprising a tubular anode enclosing portion closely embracing said anode while permitting rotation thereof, said envelope including a cathode enclosing portion of sectional dimension larger than that of the anode enclosing portion, and pole pieces sealed in the openings formed in the anode enclosing portion adjacent said cathode enclosing portion.

ZED J. ATLEE. JAMES C. FILMER.

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