US1787699A - X-ray tube - Google Patents

Description

Jan. 6, 1931. M. MORRISON 1,787,699

'x-RAY TUBE v Filed June 9, 1922 INVENTOR MONTFORD MORE/50A ATTORNEY Patented Jan. 6, 1931 .SUNITEDH STATES PATENT OFFICE. I

MoN'rrom) MORRISON, or NEW YORK, N. Y., ASSIGNOR 'ro WESTINGHOUSE ELEcrEIc AND MANUFACTURING ooMPANY, A coEroE noN or PENNSYLVANIA I X-RAY TUBE,

Application filed June 9,1922. Serial No. 566,961.

. My present invention relates to X-ray tubes.

An object of this invention is the provision of an X-ray tube which maybe operated without substantial positiveionization 0f the gas V within the tube.v

Another object of this invention is the provision of-a focusing device which will aid in suppressing ionization of the residual gas in an. X-ray tube. 1

Other objects of the invention may be perceived from a reading of the following specification.

In the operation of -X-ray tubes employing a hot cathode, the occurrence of a considerable amount of ionization of the residual gas gives rise to several deleterious effects which are well known. One. method proposed for avoiding such effects is the evacuation of the tube to the highest possible degree. To obtain such a degree of vacuum is not only an unnecessarily prolonged process but such a vacuum, when attained, is difiicult to maintain during the life of the tube. Moreover, at thehigh voltages now in use, a certain amount of the undesired ionization is obtained even in a so-called high vacuum. This ionizationinevitably results from the structure,given'certain members of the device. For example, the existence of sharp points or edgeshaving small radii of curvature on such elements as the anode and the focusing device has been found to be responsible for at least part of the gaseous ionization. That this is true may be realized when it is considered that the intensity of an electric field or potential gradient-is greater at a sharp point or edge than at a surface having large radii of curvature and that the liability of obtaining ionization is greater the higher the potential gradient or intensity of the electric: field.

I, therefore. propose an X-ray tube in which sharp points or edges and surfaces of small radii of curvature shall be eliminated from those parts of the tube where such configurations may give rise to intense electric fields which cause gaseous ionization. Ac-

cordingly, the present invention comprises a focusing device and an anode characterized by the absence of sharp points or edges and eons ionization results, or at least to a point the substitution therefor of curved surfaces having such radii of curvature that the intensity of the electric field may be reduced to a value at which no substantial amount of gasat which ionization, plays no essential role in the productionv of X-rays. The comparatively low intensity of the electric field produced by my invention allows a higher gas pressure to exist in the tube so that there is no necessity for attaining and maintaining the extremely high vacuum so desirable in tubes of the p'riorart.

In the accompanying drawings illustrating my invention,

,Fig. 1 is an elevational view, partly in section, of an X-ray tube embodying the novel form of focusing device surroundin an incandescible filamentary cathode; an

Fig. 2 is a plan view of a toroidal focusing device and a spirally-wound cathode taken on line IIII in Fig. 1.

An illustration of my invention is shown in the accompanying drawing which is a view in elevation, partly in section, of an X-ray tube comprising aspherical evacuated glass envelope 2 having oppositely extending arms 3 and 4 into which are sealed, respectively, an anode 5 and a cathode 6, the former having a leading-in conductor 7 and the latter having leading-in conductors 8 and 9. The leading-in conductors of both electrodes and the inactive parts of the electrodes themselves are preferably covered with an insulating material. Encircling the cathode 6 is a focusing device 11 for the purpose of concentrating the cathode rays into a limited area.

The feature of the anode 5 resides in its form, which, as illustrated in the drawing, that of a spheroid, although it may take other forms embodying surfaceshaving large radii of curvature with the elimination of sharp, points or edges. The material used, in the construction of the anode 5 may be the same as that usually employed. q 95 Opposite the anode or target 5 is the cathode 6 which may be a spiral of refractory conducting material such as tungsten sothat it may be heated to an electron-emitting tem-. perature. Encircling the cathode 6, the foll cusin device 11 is shown as a solid ring or term the novel feature of which consists in its having a form devoid of sharp points or edges and characterized by surfaces having end being fitted secure y over the glass stem '14. As usual, the focusing device 11 and its extension 12, both of which consist of con-, ducting material, are electrically connected to the cathode, which is shown in the drawing by a wire 15 connecting the leading-in conductor 9 to the extension 12.

In the preparation of the tube, the envelope should be exhausted of gases and vapors, means for accomplishing which are well known in the art. Thecomponentparts of the X ray device, particularly the anode and released gases and vapors.

The presence of focusing device, ould also be freed from gases and vapors; this may be accomplished, for-example, by heating the device to a high temperature in a ,vacuum and removing the The degree of vacuum to which the tube is evacuated or the pressure of the gas admitted should be such that no substantial amount of ionization will occur during the operation of the tube.

gas sufiicient to cause positlve ionization which will be harmful to the tube may be recognized by the form of the voltage-current curve and by other means known to those skilled in the art, whereby the presence of a deleterious amount of gaseous ionization may be detected.

' While I have herein described a preferred embodiment of mv invention,-it is to be understood that modifications of the same may 0 be contrived without departing from the 5' cd'envelope,

scope thereof, claims.

-What is claimed is:

1. An X'-ra'y as defined by the appended an electron-emitting cathode and an'anode therein, and afocus ing device surrounding saidcathode, said focusing device having a curved surface facing said anode and extending above and below said cathode.

2. An X-ray tube comprising an evacuated envelo an electron-emittin cathode and an anode therein, and a focusing device surrounding said cathode, the exposed surface of said focusing device being curved to 5 a degree at which the intensity of the electricalfield at the surface is reduced snfliciently to avoid objectionable concentration,

whereby the liability of gaseous ionization occurring is materially reduced.

3. An X-ray tube comprising an evacuated envelope, an electron-emitting cathode and an anode therein, a focusing device for controllin the direction of the cathode rays, said focusing device having its exposed surface so curved that the intensity of the elecdevice 11, the other ous ionization tube comprising an cvacuat-' ed envelope, an electron-emitting cathode and focusing device therefor, and-an anode, the exposed surface of said anode bein s0 curved that the electrical field at the sur ace is reduced sufiiciently to avoid objectionable concentration, whereby the liability of gaseoccurring is materially reduced. 7

5. An electron discharge device comprising an evacuated envelope and a plurality of electrodes therein, the exposed surfacesof said electrodes being so curved that the electrical fields at the surfaces thereof are reduced suflicient to avoidobjectionable concentration, whereby the liabllity of gaseous ionization occurring is materially reduced.

6. An Xray tube comprising an evacuated envelope, an electron-emitting cathode and an anode therein, and a focusing device for controllingthe direction of the cathode rays, said focusing device and anode having their exposed surfaces so curved that the electrical fields at the surfaces thereof are reduced sufficient to; avoid objectionable concentration, whereby the liability of gaseous ionization occurringis materially reduced.

7. An electrondischarge device comprising an evacuated envelope and a plurality of electrodes therein, the exposed surface of one of said electrodes being so curved that the electrical fields at the surface thereof are reduced Isufliciently to avoid objectionable concentration, whereby the liability of gasesaid envelope from which a discharge talies' curvature of such magnitude as to distribute the electrostatic fields about the same uniformly thereover.

occurring is materially .re-

place under normal conditions of operation, the end of said electrode presented to the interior of. the envelope having a degree of 9. A discharge device comprising an hermetically sealed envelope and a plurality of electrodes thereon between which a discharge takes place under normal conditions of operation, one of-said electrodes being substantially wholly convex and non-focus ing, whereby the concentration of electrostatic fields thereabout is substantially prevented.

1 10. A discharge device comprlsmgan hermetically sealed container and at least one electrode presented to the ifiterior of said container. from which a discharge takes place under normal conditions of operation, said electrode being so curved as to prevent any localized gaseous ionization occurring and reaching a large value. 3

In testimony wheref, I have hereunto subscribed by name this seventh day of June,

MONTFORD MORRISON.

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