US2205297A - X-ray tube - Google Patents

Description

K. LENz y June 18, 1940.

X-RAY TUBE Filed July 21, 19:59

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vr 13m Patented June 18, 1940 UNITI-:D STATES X-RAY TUBE y Kurt Lenz, Berlin-Lichterfelde, Germany, assignor to General Electric Company, a corporation of New York Application July 21,'1939,'seria1 Navasa-816 'f j In' Germany July 23, 1938 e e,

3 claim.l` (c1. 25o-147) This application relates to improvements in X-ray tubes. y A

In X-ray tubes provided with' an exposed target, electrons reflected from the targetsur- 5 face are free to impinge on the glass wall of the tube envelope. In order to avoidthe possibility of damage to the envelope due tofthis cause it is known to place the target at the inner end y.of a relatively long channel leading into the interior of the anode so that the target is substantially enclosed by theanode material. In order to prevent escape of electrons, while permitting'X-rays to leave in the desired direction, the anode is providedwith an outlet channel which is covered at its outer end by a kso-callect window, such window consisting of a metal layer of such thickness as to intercept high velocity electrons`.

In tubes of high capacity the presencefof a window of the type above referred to involves considerable diiiiculty in providing adequate cooling of the window. In this connection it has been proposed to use as a window material a heat-resistant metal which is capable of operating at a temperature so high as to make'feasible the dissipation of heat mainly'by radiation.- In such an arrangement, however, it has been found that thermal conduction from the window to the anode metal at the'region where the two are connected tends to produce excessive vaporization of the latter'and thus to interfere with the proper functioning of the tube. It is the principal object of my present invention to provide an im-l proved window arrangement by which this difficulty may be overcome.

The features of the invention which I desire to protect herein are pointed out with particularity in the appended claims. The invention, itself, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. l represents a longitudinal sectional View of an anode embodying the invention; Fig. 2 is a transverse sectional View of the anode of Fig. 1, and Fig. 3 shows schematically the incorporation of the anode of Fig. 1 in a complete X-ray tube.

Referring particularly to Fig. 1, there is shown a portion of an X-ray tubeancde designated by the numeral l. This anode is of a relatively massive construction and consists preferably of a highly conducting metal such as copper. At one end the anode is. provided with an openended channel 2 which leads into the interior of the anode structure.

Within the anode and adjacent the extremity dicated at 9 so that there is la region a--b of of the channel 2 there is arranged an inclined target 3 which may consist for example, of av disk of a refractory metal such as tungsten set into the body of the anode. This target yis adapted to receive the vimpingement of a beam (E) of' high velocity electrons.V Itmay be cooled by the provision of means such as an inlet pipe 5 for circulating cooling fiuid into contact with a portion of the anode structure which is in good heatv exchanging relation With the target. As a result of the. impingement of electrons on the target 3,

X-raysare emitted Yfrom the target in all directions. `In order to permit such X-rays to leave the structure only along a desiredpath the anode is provided with a second channelt which'exjtends from the vicinity of the target outwardly toward the exterior of the anode. As a result of the existence `of this channel there is projected exteriorly of the anode an electron beam which has a region of major intensity within the angle A-B and a penumbral region CL-D. In order to prevent the escape through the' channel E ci electrons which are reflected from the target 3 the outer opening of the channel is covered by. means of a relativelyy thin'metal foil 8. This foil is preferably constituted of a metal such as tantalum which is capable of operating without. evaporation at extremely high temperatures, say, on the'order of two thousand degrees centigrade or above. It is secured Ito the main body of the anode by being soldered or otherwise joined thereto at the. peripheral region a.. Y

Without the special provision shortly to be described an arrangement such as that indicated above would have a strong tendency to produce melting of the anode material at the region of contact between such material and the foil 8. The melted material would flow over the surface of the foil and eventually be evaporated onto the walls; of the envelope. 40

In order to prevent this occurrence, .means are provided for shielding a perimetricallyextending region of the foil from directradiations proceeding from the target 3. To this end ther inner wall of the channel 6 is cut away as inthe foil which is shielded by the anode structure without being in contact therewith. As a result of this arrangement a relatively considerable temperature drop may occur between the central portion b-b of the foilvand that part of the foil which is in direct contact withk the anode metal. Consequently, even though `the central portion of the foil may be operating at a temperature above two thousand degrees centi- 55 grade, the outer edges of the .foil will be at a temperature below the melting point of copper. In order to permit such a temperature drop to occur, it is of course necessary that the thickness of the foil be relatively small with reference to its effective radiating area. In order to increase the specific radiating capacity of the foil its surface maybe modiedby roughening or blackening. l l

Fig. 2 shows the window arrangement Aas viewed in another plane. In order that the radi# ating area Yof the foil 8 may be greater than that which Would be provided, for example, by a at surface, it is preferred that the foil vbe'imade to follow the outer cylindrical contour 'of the anode surface as shown. It will be understood vthat the window as a whole is of generally 'cir cular shape. ,7:

For the purpose of completeness the anode I is shown in Fig. 3 in its normal relation Hto the other parts of an ,X-ray tube. In the arrangement illustrated the anode -isY supported at one extremity of a glass envelope I-Ii by means of aglass-to--metal seal indicated at 1I I. At the other end. of the envelope there is provided a cathode comprising an electron-emittingv nlament I2. This filament is ypositioned in a slot I3 provided in a metallic focusing element I4, the latter element being in turn supported by means of a metallic cylinder ,mounted .on n.

reentrant portion of the glass envelope as inditending from the vicinity of said target toward the exterior of the v.anode in a direction of desired X-ray emissionv and `a'vvindi'nw arrangement for preventing the escape ,of electrons through said second` channel, saidwindow arrangement comprising a relatively thin foil of a refractory metal having a meltingl temperature materially above that of the material of which the main bodyV of the anode is constituted and at least on the order of 2,000 degrees centigrade, whereby the foil may be heated to a temperature of effective heat radiation Without vaporization thereof, the saidy foil being joined at its outer edges to the main body of the anode so as to close the electrons, thereby to prevent such portion of the .foil from attaining a temperature in excess of the melting point of the anode material and thus producing vaporization of the contiguous parts of the anode structure.

2. Xeray tube including a cathode, an anode havingA anlopen-ended channel directed toward saidcathGde, an X-ray-producing target positioned within said anode at the inner extremity of" said channel, a second channel extending from the vicinity of said target toward the exterior of the anode ina region of desired X-ray emission and a window arrangement for preventing. the escape of electrons through said second channel, said Window arrangement comprising a relatively thin foil of a refractory metal having a melting temperature materially above that ofthe material of which the main body of theanode is constituted and at least on the order of 2,000 degrees centigrade, whereby the foil may be heated to a temperature of effective heat radiation without vaporization thereof, the said foil being joined at its outer edges to the mainrbody of the. anode so as to close the outer end of the channel, and means extending inwardly from the wall'of the channel at a point displaced from the foil for shielding a perimetrically extending portion ofthe foil from direct radiations from said target, thereby to prevent such portion of the foil from attaining a temperature in excess of the melting point of the anode material and thus producing vaporization of the contiguous parts of the anode structure.

3. An X-ray tube according to claim 1 characterized bythe fact that the surface ofthe window foil is blackened or roughened tov increase KURT LENZ.

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