US2720607A

US2720607A - Sealed off, fine focus, long life, flash x-ray tube

Info

Publication number: US2720607A
Application number: US295132A
Authority: US
Inventors: Edward L Criscuolo; Donald T O'connor
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-06-23
Filing date: 1952-06-23
Publication date: 1955-10-11
Anticipated expiration: 1972-10-11

Description

1955 E. L. CRISCUOLO ET AL ,7

SEALED OFF, FINE FOCUS, LONG LIFE, FLASH X-RAY TUBE Filed June 25, 1952 Dn W60 mwm EGO W6 IRQO C LT D %L A w O E D R. W ATTORNEYS United States Patent (SEALED OFF, Focus, LONG LIFE, FLASH X-RAY TUBE Edward L. Criscnolo, Silver Spring, and Donald T. OConnor, Laurel, Md., assignors to the United States of America as represented by the Secretary of the Navy The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to flash X-ra'y tubes and more particularly to a fine focus X ray tube of the sealed ofl, high vacuum type having a long tube life.

In the design of hash X-ray tubes, particularly those types which are used'in high speed radiography, it is desirable that the tube have a fine focal spot to produce a welldefined image, that the tube be of the high vacuum Sealed ofi type to obviate the necessity for an elaborate vacuum pumping system to evacuate the tube, and that the tube possess a longlife. The tubes of the prior art have failed to meet one or more of these requirements. There are presently available X-ray tubes which are sealed oil but which produce a large focal spot due to the type of anode'used, and which consequently result in the production of an image lacking the requisite sharpness necessary in high speed flash radiography. There have also been attempts to produce a fine focus flash tube, but in the past these tubes have' not been of the sealed off type and have thus required a vacuum pumping arrangement for continually evacuating the tube in order to remove vaporized tungsten which is emitted from the tungsten target at high temperatures to thereby prevent accumulation of a tungsten layer on'the inner surface of the X-ray tube. The deposit of tungsten on the window through which the X-rays are emitted reduces the intensity of the X-ray and thus shortens the life of the tube, and the deposit of large amounts of vaporized tungsten on the inner walls of the tube considerably decreases the internal resistance of the tube and may eventually result in a short circuit between the anode and Cathode through the deposited tungsten coating. The resent invention overcomes these difiiculties by providin a sealed off, high vacuum tube utilizing a target consisting of a tungsten cone for producing a fine focus. A cylindrical shie'ld on which the vaporized tungsten is collected is provided for the cathode to prevent the accumulation of a tungsten layer on the inner Walls of the tube and on the X-ray window.

Accordingly, it is an object ofthe present invention to provide a harsh X-ray'tube of the high vacuum sealed off type using a comically shaped target to produce a fine focus.

Another object is to provide a fine focus flash tube which requires no external evacuating equipment.

A further object is to provide a shield for preventing the deposit of a layer of vaporized target material on the inner walls of the tube to thus prevent internal shorting.

A still further object is to provide a shield which reduces the deposition of vaporized target material on the X-ray window to maintain a high X-ray intensity throughout the long life of the tube.

Further objects and many of the attendant advantages of this invention will be readily appreciated as the same 2,720,607 Patented Oct. 11, 1955 becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

Fig. 1 illustrates one embodiment of the X-ray tube showing a cross sectional view taken along a plane passed longitudinally through the tube;

Fig. 2 shows a transverse cross-sectional view of the tube taken along a line corresponding substantially with line 2-2 of Fig. l; and

Fig. 3 shows a transverse cross-sectional view of the tube taken along a line corresponding substantially with line 3-3 of Fig. 1.

Referring now to the drawing, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Fig. 1 (which illustrates a preferred embodiment) a glass envelope 10 for the X-ray tube which is provided with a re-entrant portion 11 at the rear thereof and an X-ray Window 12 at the front. Extending along the longitudinal axis of the tube and protruding beyond the rear portion is a conducting rod 13, which may be made of Kovar, Fernico, German silver, or the like, these materials being chosen since their temperature coefficient of expansion is substantially the same as that of glass to thus enable a seal to be maintained between the conducting rod and the reentrant portion 11 of the glass envelope with a change in temperature.

Secured to the front portion of the conducting rod 13 is a conieally shaped target 14 in which the axis of the cone extends along the longitudinal axis of the tube and the base of the cone abuts the front portion of the conducting rod. The cone may be secured to the rod by means of a weld of stainless steel, nickel, or the like, or may be attached in other suitable manner. It is contemplated that the target he made of tungsten. However, other materials having a high melting point and a high atomic number which provide a substantial quantity of X-rays when bombarded with electrons, may be used.

Extending through the front face of the tube are a pair of conducting lead wires 16 and 17 which may be made of Kovar, German silver, or other materials having properties similar to those of the conducting rod 13 so as to maintain a seal between the glass envelope and the lead wires upon change in temperature. The lead wire 17 is connected to an annular plate cathode 18 which is positioned perpendicular to the longitudinal axis of the tube so that this axis passes through the center of the aperture in the plate and the apex of the conical target 14 is positioned at approximately the center of the aperture in the plate. The lead Wire 16 is connected to a cathode disc 19 having a flared portion 20 and a central opening through the flared portion of approximately the same diameter as the aperture in the annular plate 18. The disc 19 is positioned parallel to the plate 18 so that the central opening of the flared portion and the aperture in the plate are alined and so that a small space exists between the edge of the flared portion 20 and the plate 18. This spaced relationship is maintained by a plurality of insulating glass beads which are secured to the lead wires 16 and 17 and which are positioned in spaced relationship around the plate 18 and the disc 19 within the tube. A cylindrical sleeve 22 is secured to the outer edge of the plate 18 in any suitable manner, such as by welding the tabs 21 to the plate, whereby the sleeve extends rearwardly from the plate so as to encircle the conical target 14 and a portion of the conducting rod 13. A hollow shield 24 is affixed to the disc 19 in any suitable manner, such as by welding the tabs 23' to the disc, so that the shield extends forwardly from the disc to a position near the X-ray window 12.

A positive high voltage of approximately kilovolts is impressed on the target 14 from a suitable source, for

' electrons emanated from the cathode.

instance, from a charged capacitor system well known in the prior art and disclosed in United States Patent 2,311,705 to C. M. Slack. In a manner similar to that shown by Slack, the leads 16 and 17 of the present tube may be connected to a pulse transformer whereby a pulse is applied across the cathode gap between the plate 18 and the flared portion 20 at a predetermined instant.

The charged capacitor may then. discharge along the conducting rod' 13, the target anode. 14, and through the tube to the cathode at groundpotential. The spark across the cathode gap developed between the plate 18 and the flared portion 20 causes the cathode, which may be made of tantalum, stainless steel, brass, or other such materials which do not evolve gasses under bombardment and which consequently are serviceable in a vacuum, toemit electrons which are directed towards the target 14; The target 14, the temperature of which has beencouside'rably raised by the high voltage discharge focal point will'result, whereas if the target is moved.

rearwardly of the plate 18 eventually a point is reached in which the spacing between the target and the cathode is too great and an insuificient supply of'X-rays is produced. Therefore,'the positioning of the target with respect to' the cathode. will be determined by the size of the focal spot desired and by the maximum spacing which may occur between the target and the cathode to attain the requisite X-ray intensity.

' .The bombardment'of the apex of the target 14 by electrons from the cathode plate 18 and the cathode disc '19 causes X-rays to be emitted from theapex of the cone which are directed along the longitudinal axis of the tube toward the X-ray window. During the high voltage discharge from the target to the cathode, the tungsten target is heated above its melting point, vaporizing a portion of the tungsten. Were it not for the presence of the sleeve 22 and the shield 24 this vaporized tungsten would 'be deposited on the inner walls of the envelope and f'the re-entrant portion 11 to eventually cause a short of these shields and thus prevents the accumulation of a tungsten deposit on the'inner surface of the envelope 10. The'shield 24 also aids in preventing the deposition of vaporized tungsten on the inner surface of the X-ray window 12. If a tungsten layer is deposited on the X- ray window, the X-ray intensity of the tube will be considerably diminished inasmuch'as tungsten is a very dense material which inhibits the passage of X-rays therethrough. The shield 24,'however, collects a large portionof the vaporized tungsten which would otherwise be'deposited on the X-ray window. Due to the high pocenter point of'the aperture of the secondplate is also.

Use of the sleeve 22 and the shield 24 causes V,

V 4 angles may be used, since a smaller angle cone produces an even finer focus and a larger angle cone yields a somewhat larger focal spot.

Obviously many modifications and variations of. the

present invention are possible in the light of the'above teachings. It is therefore to be understood that within the. scope of the appended claims the invention may be practiced otherwise than as described.

What is claimed is: i

1. In combination, a high vacuum sealed off X-ray tube, a conducting member extending longitudinally of the tube, a conically shaped target secured to said conducting member, a first apertured cathode plate positioned so that the apex of the cone is located at approximately the center of the aperture in the plane of said first plate, and a second apertured cathode plate positioned parallel to said first plate so that the apertures in the first and second plates are alined whereby X-rays are produced from the target through the alined apertures to a fine focal point when the. target is bombarded by electrons from the cathode. j

2. In combination, a high vacuum' sealed off. X-ray tube, a conducting member extending longitudinally of the tube, a conically shaped target secured to saidcon point of the aperture is'located on the longitudinal axis of the tube and the plate is positioned near the apex of the cone, and a second apertured cathode plate'in par-- allel spaced position from the first plate so that the located on the longitudinal axis 'of. the tube whereby X-rays are emitted from the target directed along the longitudinal axis of the tube to a fine focal point when the target is bombarded by electrons from the cathode.

3. A fine focus flash X-ray tube comprising, a high vacuum sealed 'ofi envelope, a pair of spaced circular apertured cathode plates, ,a pointed conically shaped target for producing X-rays having .a fine focal point when bombarded by electrons from the cathode, the apertures of said cathode plates and the axis of said target being aligned along the longitudinal axis of said tube, and means for collecting vaporized target material:to prevent deposition of the target material on the inner walls of the envelope to thereby provide ta long life X-ray tube.

4. A fine focus flash X-ray tube comprising,.a high vacuum sealed off envelope, a pair of spaced circular apertured cathode plates, a pointed conically shaped of said cathode plates and the axis of said target being" aligned along the longitudinal axis of said tube, means surrounding the target and extending rearwardly thereof .for collecting vaporized target material and prevent its tential gradient which exists between the cathode and the target at the instantthe tube is flashed and for a short period thereafter, the vaporized tungsten which is produced at the target is directed towards the cathode and the cathode shield. Therefore, nearly all of the vaporized deposition on the inner walls of the envelope, and means extending forwardly of the target in'the direction of X-ray emission for preventing deposition of vaporized target material on the surface "of the envelope through which the X-rays are emitted. V I a r 5. A fine focus flash X-ray tube comprising a high vacuum sealed off envelope, an X-ray window in the envelopes surface, an apertured cathode plate, a pointed conically shaped target having the apex thereof positioned substantially at the center of the cathode aperture for i producing X-rays having a fine focal spot when bombarded'by electrons from the cathode, the center of the aperture of said cathode and the axis'of said target being aligned along the longitudinal 'axis of said tube, and a hollow shield extending forwardly of the cathode toward the X-ray window in the direction of emission of X-rays from the target so as to prevent the accumulation of vaporized target material on the X-ray window to thereby produce a' tube having a long life and high X-r'ay intensity.

6. A fine focus flash X-ray tube comprising a high vacuum sealed off envelope, an Xn'ay window in the envelope surface, an apertured cathode plate, a pointed conically shaped target having the apex positioned substantially at the center of the cathode aperture for producing X-rays having a fine focal spot when bombarded by electrons from the cathode, the center of the aperture of said cathode and the axis of said target being aligned along the longitudinal axis of said tube, and a pair of cylindrical shields one of which extends rearwardly from the apex of the conical target to surround the target and the other of which extends forwardly of the apex of the target toward the X-ray window to prevent deposition of vaporized target material on the inner surface of the walls of the envelope and on the surface of the X-ray window to thereby produce a tube having a long life and high X-ray intensity.

7. A fine focus flash X-ray tube comprising a high vacuum sealed E envelope, an apertured cathode plate, a conducting member extending along the longitudinal axis of the envelope, a pointed conically shaped target secured to the conducting member, said target having the apex positioned substantially at the center of the cathode aperture so that the center of the aperture of said cathode and the axis of said target are aligned along the longitudinal axis of said tube causing X-rays to be directed from the apex of the conical target along the longitudinal axis of the envelope to produce a fine focal point when the target is bombarded by electrons from the cathode, and a cylindrical shield surrounding the target and a portion of the conducting member so that the axis of the cylindrical shield coincides with the longitudinal axis of the envelope whereby the deposition of vaporized target material on the inner surface of the envelope walls is prevented.

8. A fine focus flash X-ray tube comprising a high vacuum sealed off envelope, a pointed conically shaped target for producing X-rays, a pair of spaced apertured cathode plates positioned so that the apex of the cone is positioned at approximately the center of the aperture in the plane of the first cathode plate whereby the target is bombarded by electrons from the cathode plates to produce the X-rays, and a shield secured to the cathode plates so as to surround the target and prevent the accumulation of the deposited target material on the inner surface of the walls of the envelope.

9. A fine focus flash X-ray tube comprising a high vacuum sealed off envelope, a conducting member extending longitudinally of the envelope, a pointed conically shaped target secured to said conducting member within the envelope for producing X-rays, a pair of spaced apertured cathode plates positioned so that apex of the cone is located at approximately the center of the aperture in the plane of the first cathode plate whereby the target is bombarded by electrons from the cathode plates to produce X-rays, and a cylindrical shield, the axis of which coincides with the longitudinal axis of the envelope secured to said cathode plates and surrounding the target and a portion of said conducting member so that the deposition of vaporized target material on the inner walls of the envelope is prevented.

10. In combination, a high vacuum sealed off X-ray tube, a conically shaped target, a pair of spaced apertured cathode members positioned so that apertures are alined and the axis of the conical target coincides with the center line of the alined apertures whereby X-rays are directed along the center line to a fine focal point when the target is bombarded by electrons from the cathode, a hollow sleeve attached to one of said cathode members so as to surround the target, and a hollow shield secured to the other to said cathode members and extending in the direction of the emission of the X-rays, said shield and said sleeve serving to prevent the deposition of vaporized target material on the inner surface of the walls of the tube.

11. In combination, a high vacuum sealed off X-ray tube, an X-ray window in the tube surface, a conically shaped target for producing X-rays, a pair of spaced apertured cathode members positioned so that the apertures are alined and the axis of the conical target coincides with the center line of the alined apertures whereby X-rays are directed along the center line to a fine focal point when the target is bombarded by electrons from the cathode, a hollow sleeve secured to one of said cathode members so as to surround the target, and a hollow cylindrical shield secured to the other of said cathode members and extending toward the X-ray window to collect vaporized target material and prevent its deposition on the surface of the X-ray window whereby a long life X-ray tube having a high X-ray intensity is produced.

12. In combination, a high vacuum sealed off X-ray tube, an X-ray window in the tube surface, a conducting member extending longitudinally of the tube, a conically shaped target secured to said conducting member within the tube so that the axis of the cone coincides with the longitudinal axis of the tube, a first apertured cathode plate positioned so that the center point of the aperture is located on the longitudinal axis of the tube and the plate is positioned near the apex of the cone, a second apertured cathode plate in spaced position from the first plate so that the center point of the aperture of the second plate is also located on the longitudinal axis of the tube whereby X-rays which are emitted from the target upon bombardment by electrons from the cathode are directed along the longitudinal axis of the tube to a fine focal point, a hollow sleeve secured to the first plate so as to surround the target and a portion of the conducting member, and a cylindrical shield secured to said second cathode plate and extending towards the X-ray window in the direction of emission of the X-rays so as to collect vaporized target material and prevent deposition of that material on the surface of the X-ray window and the inner surface of the tube.

13. In combination, a high vacuum sealed off X-ray tube, an X-ray window in the tube surface, a conducting member extending along the longitudinal axis of the tube, an X-ray producing target secured to said conducting member, a first cathode plate positioned near the target so that the plane of the plate is perpendicular to the longitudinal axis of the tube, a second cathode plate positioned parallel to the first plate with a slight space between the plates, a first conducting shield secured to the first plate so as to surround the target and a portion of the conducting member to prevent the deposition of vaporized target material on the inner walls of the tubes, and a second conducting shield secured to the second plate and extending towards the X-ray window in the direction of the emission of X-rays from the target to prevent the deposition of target material on the Window.

14. In combination, a high vacuum sealed off X-ray tube, an X-ray Window in the tube surface, a conducting rod extending along the longitudinal axis of the tube, an X-ray producing target secured to said conducting rod, a first apertured cathode plate positioned near the target so that the plane of the plate is perpendicular to the longitudinal axis of the tube, a second apertured cathode plate positioned parallel to the first plate with a slight gap between the two, a first cylindrical shield secured to the first plate so as to surround the target and a portion of the conducting rod to prevent the deposition of target material on the inner Wall of the tube, and a second cylindrical shield secured to the second plate and extending towards the X-ray window in the direction of emission of X-rays from the target so that the X-rays pass from the target through the apertures in the two plates and through the second cylindrical shield to the X-ray window, said shields serving to prevent the deposition Refel ences Cited in the file of this patent UNITED STATES PATENTS Holst et a1. July 6, 19 26 Lilienfeld Feb. 8, 1927 Holst et a1 June 14, 1927 Forde Mar. 6, 1934 Bouwers Sept. 25, 1934 Huppert etal. Sept. 8, 1936 Cassen Aug. 4, 1942 Atlee Aug. 24, 1943 De Graaf Oct. 31, 1944