US2073672A - X-ray tube and cathode structure therefor - Google Patents

Description

March 16, 1937. N. c. BEESE X-RAY TUBE AND CATHODE STRUCTURE THEREFOR Original Filed July 12, 1935 INVENTOR 2%. c 55555 BY To ATTORNEM Patented Mar. 16, 1937 UNITED STA X-RAY TUBE AND CATHODE STRUCTURE THEREFOR Application July 12, 1933, Serial No. 680,013 Renewed January 22, 1937 12 Claims.

The invention is directed to an electron dis charge device and especially to a novel type of cathode construction therefor. In one of its aspects the invention is specifically concerned with a novel cathode construction and more particularly one that may be advantageously employed in a device such as an X-ray tube where a focal spot of predetermined configuration and size may be desirable and is sometimes a prelO requisite.

An object of my invention is to provide improved X-ray tubes which may be readily produced andv all of which may be employed to provide focal spots of the same and. predetermined l5 dimensions.

Another object of my invention is to provide an improved cathode structure.

A further object of my invention is to provide an improved cathode structure which may be manufactured at a moderate cost.

Other objects and advantages of my invention will be readily apparent from the following description and drawing wherein,

Figure 1 represents a longitudinal cross sectional View with some of the parts in elevation of an X-ray tube embodying my invention.

Figure 2 is a plan view taken on line IIII of Figure l.

' Figure 3 is a cross sectional view taken on line III-III of Figure 2.

Figure 4 is a cross sectional View taken on line IV-IV of Figure 3.

As shown'in Figure l the X-ray tube comprises a dielectric enclosing envelope ill having a reentrant tube H at one end and a reentrant tube (not shown) at the other end thereof. Extending in said last mentioned reentrant tube and sealed to said envelope is a copper anode I2 having a target of tungsten or the like embedded in the free end thereof. The reentrant tube H has its free end in the form of a press It! in which are sealed metallic supports I4, I 5, l6 and H. The supports it and H are electrically connected to a suitable cap l8 and serve as electrical conductors for the filament of the cathode structure, and the supports I l and i5 merely serve as supporting means for the cathode structure. A metallic thimble i9 is secured to the conductor ll and surrounds the press to protect the press and upper part of the reentrant stem ll from bombardment.

According to my invention the cathode structure comprises essentially a focusing device and a thermionicallyactive body. The focusing device comprises a metallic block 20 composed of nickel-iron, molybdenum or the like. Extending along the entire length of said block is a groove 2!, with sides thereof in cross section being in the form of arcs of a circle. The bottom portion 22 of the block has a slot 23 extending 5 from one end thereof to a point adjacent the other end thereof. The slot 23 is rectangular in cross section and has its upper end coincident with the lower end of groove 2| and its lower end coincident with the lower face of the bottom 22. The groove 2! and the slot 23 form a slot extending to both the upper and lower faces of the block, a portion of the slot extending to two side limiting faces thereof and another portion to only one side limiting face thereof.

A thermionically active element 24 is located in the block 20. The element 24 is in the form of a coiled filament composed of tungsten or the like and has its ends depending in the direction of the depth of the slot 23. One end of the filament 24 is electrically secured by welding to a short length of a rigid metallic strap 25. The strap 25 is connected in like manner to the lower face of the bottom 22 so that the potential of the cup shall be approximately the same as that of the filament.

The other end of the filament is secured by Welding or other appropriate means to the upper end of the support It. The so mounted filament or cathode 24 has its major axis parallel to the longitudinal center line of the groove 2!. The cathode z l'is so disposed that it is located centrally between the lower edges of the groove Zl and its central axis is substantially parallel to and in the horizontal plane of the lower edges of said groove 2!. v

In the course of my experimentations with cathode structures adapted to be employed in X-ray tubes, I have found that the focal spots obtained on anodes of tubes of this character may be of variable design depending upon the cathode structures employed. Since I desire to provide cathode structures which may be readily reproduced to provide the same type of focal spots of like pattern, my efforts were directed towards the determination of the critical factors which must be known in order that the desired result might be accomplished.

Focal spot patterns that may be obtained may consist of a pair of spaced heavy lines between which is located a light field containing therein a pair of lighter lines, a pair of heavy lines with a light area of substantially uniform intensity therebetween, or a pair of heavy lines with a lighter 1ine adjacent and outside of each of said heavy lines and a light area including all of said lines.

The size and energy distribution of the focal spot I have found may be controlled by control- 5 ling the width and depth of the groove 2!, the

width of the slot 23 and the distance that the filament is placed from the upper limit of the groove 2 l the filament being disposed with its longitudinal axis parallel to the sides of the slot and equally spaced therefrom and lying in the horizontal plane of said cup. In order that the focal spot, comprising a pair of parallelly spaced heavy lines between which is a lighter area of uniform intensity, may be obtained and which I prefer to be produced in my X-ray tube, I have controlled the dimensions of the groove 2f, the slot 23 and the distance between the filament and the upper limit of the groove 2|. This result may be accomplished by having the upper width of the groove 2| equal to about 5.8 to 6.0 millimeters, the

depth of the groove 2! equal to 3.0 to 3.5 millimeters, the width of the slot 23 equal to 2.0 millimeters and the distance between the upper limit of the groove and the central longitudinal axis of 25 the filament equal to about 3.0 to 3.5 millimeters. In order that a wider spot may be obtained, the width of the groove 2! may be equal to 7 .0 millimeters, the depth of the groove 2i equal to .128 of an inch, the width of the slot 23 equal to .150 .210 of an inch and the distance between the upper limit of the groove 2| and the longitudinal central axis of the filament equal to .128 of an inch. If a still wider focal spot is desired, the distance between the upper limit of the groove 2| is equal to 8.25 millimeters, the depth of the groove is equal to 3.5millimeters, the width of the slot equal to 4 millimeters and the distance between the upper limit of the groove 2! and the central longitudinal axis of the filament equal to 3.5 milli meters.

In all of the above cases the distance between the filament 24 and the center of the target of the anode I2 is about 18 millimeters. Even with spots whose widths and pattern are predetermined, it is necessary to provide a means for controlling the length of said spots. Heretofore small end L-shaped plates have been secured to the cup and located adjacent the filament for this purpose. The position of these plates is so critical and a small displacement thereof in the direction of the anode may make an appreciable change in the focal spot length.

In order to obviate said difficulty and so that blurred focal spots may be obviated and so that well defined focal spots may be obtained, in order that the size of the focal spots may be of a predetermined and of a certain size, and so that any quantity of readily reproducible cathode structures adapted to be employed to provide the same size and shaped focal spots on an anode, may be readily manufactured, I have provided the construction illustrated. The filament 24 is of a predetermined length depending upon the length of the desired focal spots as well as upon other factors.

Extending across the groove 2| and perpendicular to the length of the coiled filament are two parallelly spaced short heavy molybdenum, nickel-iron or iron wires or pins 26 and 21. These pins are of circular cross sectional diameter about 40 to 80 mils and are located in openings located in the sides of the cup and adapted to accommodate the same. The pins 26 and 21 have portions thereof respectively in line with a vertical line perpendicular to the horizontal plane of the cup and passing through the extreme outer coils thereof. The pins 26 and 27 are located vertically adjacent said outer coils but are spaced an appreciable distance therefrom. The vertical distance between the filament and an adjacent pin is of the order of 1 or 2 millimeters.

With this construction it is possible to obtain a well defined focal spot on the anode. The focal spot obtained with this construction does not exhibit fanning and feathering at the transverse extremities thereof because of the pins 26 and 21 that are in electrical contact with the cup and, therefore, are at the same potential as the cup and filament 24. These pins may always be mounted in the same spaced relationship by placing the cup in a jig, drilling holes therein and securing pins 26 and 2'! in said holes.

In order to further insure the obviation of any chances of a fanned or feathered focal spot, I provide the shields 28 and 29 composed of rigid sheet metal, such as nickel or the like, which may be suitably cut and otherwise shaped.

The shields i8 and 29 are so cut, shaped and mounted that they are in electrical connection with the cup, whereby the electrons emanating at the cathode 2% may reach the anode only by passing between the pins 26 and 21. The shield 28 has a portion thereof which extends entirely across the slotted open ended lower portion of the cup to form a complete barrier thereacross. Another portion of the shield is bent at right angles to the aforementioned portion, is of substantially rectangular contour and is of such a width that when parallel to the base of the cup it ts rather closely to the sides of the lower portion of the groove 2!. This rectangular portion extends from the end of the cup towards the, other end thereof and. has another portion in the form of a wing which is bent and extends upwardly and towards the pin 26. This last named portion is of such size and contour that its periphery is closely adjacent the sides of the cup defining the groove 2! and the lower portion of the periphery of the pin 26.

The shield 29, which serves the same purpose as the shield 28, has one portion thereof electrically secured by welding to the upper face of the cross piece of the cup defining one end of the slot 23. The other portion of the shield 29 is integral with said first mentioned portion, is bent and extends upwardly towards the pin 27. This last portion is also of wing shape and has its periphery closely adjacent the sides of the cup defining the groove ZI and to the lower portion of th periphery of the pin 21.

The cup 29 has grooves in the sides thereof to accommodate the supports 2d and [5 which are secured thereto by a welding operation. The transverse side of the cup which defines the lengthwise limit of the slot 23 also has a groove therein to accommodate the support and conductor I? that is electrically and mechanically secured thereto by a welded or other means.

My invention is not to be limited to the specific structure shown because it is susceptible to modifications, but is to be limited only by the prior art.

What is claimed:

1. A cathode structure comprising a focusing block and a filament, said focusing block having a groove in one face thereof, said filament being located in said groove, a pin extending across said groove and being secure to said block and said pin being located adjacent one end of the effective length of said filament.

2. A cathode structure comprising a focusing block and a filament, said focusing block having a groove in one face thereof, said filament being located in said groove, a'pin extending across said groove and being secured to said block, said pin being located adjacent one end of the effective length of said filament and a shielding means secured to said block and having a portion thereof extending across said groove to substantially completely fill the cross sectional space of said groove between said filament and said pin.

3. A cathode structure comprising a focusing block and afilamena'said focusing block having a groove therein, said filament being located in said groove, a plurality of spaced pins secured to said block, said pins being located between one face of the block and said filament.

4. A cathode structure comprising a focusing block and a filament, said focusing block having a groove therein, said filament being located in said groove, focusing means secured to said block and adjacent said filament, said means including a pair of spaced pins.

5. A cathode structure comprising a focusing block and a filament, said focusing block having a slot extending therethrough and to the upper, lower and one other limiting face of said block, said filament being located in said slot, a pin of curvilinear periphery secured to said block and located above and adjacent said filament, said pin extending across said slot.

other end secured to a support secured to said I block, a plurality of, pins extending across said slot and secured to said block, shielding means secured to said block and having portions thereof directly across the space adjacent said pins and 7 across said block so that the electrons emanating at the cathode and striking the anode must all pass between said pins.

7. An X-ray tube comprising an envelope having a press, an anode and a cathode structure therein; a plurality of supporting wires secured to said press, said cathode structure including a focusing block having a slot, said supporting wires secured to said block, a plurality of leading-in conductors secured to said press and extending interiorly and exteriorly of said envelope,

' one of said conductors, also being secured to said block, a filament mounted on said block and secured to said other conductor, said filament having-its other end electrically connected to said block, a plurality of spaced pins extending across said slot and secured to said block, shielding means secured to said block and extending across the slot to prevent any substantial quantity of electrons emanating at the cathode from reaching the anode without passing between said pins.

8. A cathode structure comprising a focusing block and a filament, said focusing block having a slot extending therethrough and to the upper,

lower and one other limiting face thereof, said filament being located in said slot, focusing pins of curvilinear periphery secured to said block and located above and adjacent said filament, said pins extending across said slot.

9. A cathode structure comprising a focusing block and a filament, said block having a slot eX- tending therethrough and to the upper, lower and one side ofv the limiting face thereof, said filament being located in said slot, a plurality of pins located above said filament and extending across said slot and secured to said block, said pins and said block serving as a focusing means for electrons that emanate from said filament, the peripheries of said pins being curvilinear.

10. An X-ray tube comprising an envelope having a press, electrical conducting means secured to said press, an anode and a cathode structure within said envelope, said means connected to said cathode structure, said cathode structure including a focusing block, said focusing block having a slot extending therethrough and to the upper, lower and one other limiting face thereof, a

filament located in said slot, a plurality of spaced pins extending across said slot and secured to said block, shielding means secured to said block and extending across said slot to prevent any substantial quantity of electrons emanating at the filament from reaching the anode without passing between said pins.

11. A cathode structure comprising a focusing block and a filament, said block having a slot divided into an upper portion and a lower portion, the upper portion constituting a groove in the upper part of the block and extending from one end of the block to the other end, and the lower portion constituting an aperture in the lower part of the block, saidfilament being located in said aperture, a plurality of pins of. curvilinear periphery secured to said block and extending across the groove in said block adjacent the ends of the filament disposed in said aperture.

12. A cathode structure comprising a focusing block and a filament, said block having a slot divided into an upper portion and a lower portion, the upper portion constituting a groove in the upper part of the block and extending from one end of the block to the other end, and the lower portion constituting an aperture in the lower part of the block, said filament being located in said aperture, a plurality of pins of curvilinear periphery secured to said block and extending across the groove in said block adjacent the ends of the filament disposed in said aperture, shielding means secured to said block and having portions thereof extending across said block to substantially completely fill the crosssectional space of the groove in said block.

NORMAN C. BEESE.

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