US2894163A - Electron discharge devices - Google Patents

Description

y 7, 1959 R. K. ORTHUBER ET AL 2,894,163

ELECTRON DISCHARGE DEVICES Filed Oct. 21, 1955 Fig. L

IN V EN TORS. RICHARD K. ORTHUBE R CHARLES v STANLEY y cmn. 1.. DAY

ATTORNEY U ted rates Patent ELECTRON DISCHA'RGE DEVICES Richard K. Orthuber and Charles V. Stanley, Fort Wayne,

and Cyril L. Day, Huntington, Ind., assignors to International Telephone and Telegraph Corporation Application October 21, 1955, Serial No. 541,996

Claims. (Cl. 313-149) This invention relates to the electron discharge devices comprising an envelope and two spaced electrodes having chemical constituents which may be chemically incompatible with each other. This invention is more particularly directed to structures and to methods of manufacture which will prevent the contamination of one chemical constituent by another within the envelope of the discharge device.

In tubes having a photocathode and a fluorescent screen, for example, chemical elements for these electrodes are usually mutually poisonous with respect to each other. During manufacture the envelope and its parts must be heated to high'temperatures during exhaust, and unfortunately these temperatures are above the evaporization temperatures of some of the more active elements for these electrodes.

By diffusion, these vapors can migrate throughout the envelope and contaminate other electrodes.

The object of this invention is an improved envelope construction and method of manufacture by which the electrodes having incompatible vaporizable substances can be isolated one from the other.

The structure by which the objects of this invention are attained comprises a partition across the envelope and a shutter in the partition which can be opened or closed. The shutter can be closed to isolate the two incompatible electrodes during heating operation, yet can be opened to permit normal operating interaction between these electrodes.

The. above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood'by reference to the following description of i an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a horizontal sectional view of an electron discharge device employing this invention; and

Fig. 2 is a sectional view taken along line 2--2 of Fig. 1.

The particular electron discharge device as shown in Fig. 1 contains a photocathode composed of cesium or other alkali metals as well as a phosphor plate composed of light metals suchas zinc with silicon or sulphur and oxygen. Zinc orthosilicate, commonly known as Willemite, or compounds containing zinc sulphide, all carrying the familiar family name of phosphors, can be contaminated and made inoperative by minute quantities of cesium from a nearby photocathode. Where two such electrodes must be de-gassed and activated in a common envelope, the problem of preventing the migration of cesium vapor to the phosphor containing surfaces becomes formidable.

In Fig. 1, the cesiated photocathode 1 is placed at one end of the tubular envelope 5 opposite the phosphor plate 2. The photocathode and the phosphor plate each comprise plateglass disks hermetically sealed along their peripheries to metal sleeves 3 and 4. In the finished tube cesium is formed on the inner surface of plate 1. The inner surface of plate 2 carries the phosphor layer. The envelope 5 comprises two end-to-end tubular portions 6 and 7. In the example shown, these tubular portions are of glass, although metal envelopes are also contemplated. The opposed ends of the tubular portions of 6 and 7 are sealed to metal flanges S and 9, respectively, the flanges being flat and radially coextensive so that the two flanges can be placed face-to-face and rigidly joined. According to an important feature of this invention, the flat disk 20, of the same outer peripheral dimensions as the flanges 8 and 9, is laid between the two flanges so that the registering edges of the disk and flanges may be welded or brazed to hermetically seal the disk and flanges together. The resulting structure comprises a tubular envelope with a transverse partition firmly anchored in the envelope wall. Other electrodes within the envelope may thus be mounted upon disk 20 and since the mounting operations may be accomplished before assembly of the envelope, close manufacturing tolerances are easily obtained.

In the particular tube illustrated, posts 21 are erected from the disk 20 and carry focusing electrodes 22. Centrally in disk 20 is stamped a large window 20a, the

window being suflicient in size to expose the full face of the photocathode l to the face of the phosphor plate 2. In the particular electron image tube shown, a collector screen 23 is conveniently attached to the under side of the disk 20 over the opening 20a. Spaced from and parallel to the collector screen is the storage target screen 24 also anchored to disk 20. In operation of the particular tube of Fig. l, a light image is projected upon a photocathode l. Electrons are emitted from the inside surface of the plate 1 of the cathode, the number emitted from each element of the picture being dependent upon the intensity of the light projected on that element. Hence, an electron image of the scene is formed which may be accelerated down the tube by appropriate potentials on the accelerating rings 22. A solenoidal focusing coil, not shown, may be placed around the envelope. The electron image without substantial distortion falls upon the storing target 24 and the dislodged secondary electrons move to the collector screen 23.

- It has been found that even minute quantities of cesium, if allowed to contact the phosphor coated. on plate 2 or settle on the storage target 24 or the collector screen 23, effectively render the tube inoperative. Since metallic cesium is unstable in air, it must be introduced to the envelope in vapor form and condensed upon the photocathode. By proper baking, and selective heating as by HP induction, it has been found that cesium can be driven from most metal and glass surfaces and caused to condense or settle upon the photocathode where it is desired. A notable exception to this phenomenon of the ,movement of cesium within the envelope is encountered where the storing target 24 and the chemically sensitive phosphors of plate 2 are present in the envelope. There is no known method for reclaiming a phosphor once it has been poisoned by cesium.

It has been found that the cesium can be effectively cut off from the storing target and phosphor plate by shutters 25 movable across opening 20a of disk 20. As shown in Fig. 2, the shutters may comprise flat, semicircular plates hinged at 26 so that the shutters can swing outwardly to uncover the shutter opening or swing inwardly to close the opening. The shutters may be flat metal stampings and the pivots may comprise simple loose-fitting rivets. A batten attached to one shutter will effectively close the crack between the two shutters. Such shutters may be moved into or out of closed position by gravity, by magnet devices, or other means. By ro- Patented July 7, 1959' tating the envelope to the proper position, for example, the shutters may be caused to drop open or close. A lock or latch of any desired detail may be employed to hold the shutters in one or the other position. The shutters, for example, may snap behind spring latches to hold them in their open position.

Tip-off, tubulations 3.0 and 31 are shown connected to the envelope of Fig. 1, one tabulation being connected to the vacuum pumps and the other connected to a source of cesium. After the envelope has been baked and. pumped to millimeters of mercury or less, and de-gassing. has been completed, silver is evaporated from a filament, not shown, near the plate 1 to form a thin film of silver. The silver is then oxidized by the introduction of oxygen through one of the tubula'tions, whereupon the silver layer becomes almost invisible. Sufiicient cesium vapor is, then emitted through one tubulation to cause the oxidized silver to change to a visible bluish or brownish color. Alternatively, the cesium may be introduced in solid compound on a filament or in a gettertype' pellet: which. can be heated to release the cesium vapor. The. metal parts within the envelope are then selectively heated to drive the cesium from those surfaces and to cause the cesium to condense on the photocathode surface. After final exhaust to the required low pressure, the tubulations are both sealed ofi.

While cesium has been mentioned throughout this disclosure, anyof the alkali metals are contemplated. Any metal which is toxic with respect to the image storage portion of the tube: may be used without regard to the toxicities of those. metals to the phosphors. Strangely, the alkali metals will notpass through the cracks around the shutter but, appear to be trapped and held by the overlapping, metal parts of the shutter and the disk 20. The sensitivity of electron image tubes of the type described is materially increased by the use of the partition and shutter. The disk 20' not only efiectively protects the electrodes in one portion of the envelope from the chemical efiects of electrodes in the other portion, but provides a broad rigid foundation upon which to mount the electrodes of the tube.

Whilev we have described above. the principles of our invention in connection with specific apparatus, it is to be Clearly understood that this description is made only by way of example and not as a limitation to the scope, of our invention.

What is claimed is:

1. An electron discharge device comprising an envelope, two chemically-sensitive electrodes spaced apart in the: envelope, a partition transversely across the envelope between the two electrodes and respectively spaced therefrom, an. enlarged window in the partition through which the two electrodes can operatively interact, and a flat shutter mounted on the partition and abutting one side thereof, said shutter being selectively movable in a plane parallel to the plane of said partition across the opening.

2. In combination, an. envelope having two end-to-end tubular portions. of glass, two metal rings, each with a flange, the opposed ends of said portions being sealed to the. metalrings, said flanges being flat and extending radially, a metal' disk substantially equal in circumferential extent to said flanges disposed transversely across the envelope and between the flanges, the flanges and disk being hermetically sealed together, metal sleeves coaxial with the envelope and sealed, respectively, in the outer ends of said tubular portions, a glass plate in each sleeve and peripherally sealed to said sleeve, a photocathode coating on the inner surface of one plate and a phosphor coating on the inner surface of the other plate, said disk having a central opening. substantially coextensive with said coatings, and a pair of semi-circular plate members respectively pivotally mounted on said disk and abutting one side thereof, said plate members forming a shutter and being respectively selectively movable in a plane parallel to the planeof said disk across said opening to close the same.

3. An electron discharge device comprising an envelope, two chemically-sensitive electrodes spaced apart in the envelope, a partition transversely across the envelope between the two electrodes and respectively spaced therefrom, said partition having an enlarged: window formed therein through which the two electrodes can operatively interact, and a flat. shutter pivotally mounted on said partition and abutting one side thereof, said shutter being selectively movable in a plane parallel to the plane of said partition across said opening.

4. An electron discharge device comprising an envelope, two chemically-sensitive electrodes. spaced apart in the envelope, a partition traversely across the envelope between the two electrodes and respectively spaced therefrom, saidpartition having an enlarged window formed therein through which the. two electrodes can operatively interact, and a pair of semi-circular plate members respectively pivot-ally mounted on said partition and abutting one side thereof, said plate members forming a shutter and being respectively selectively movable in a plane parallel to the plane of said partition across said opening to-close the same.

5. An electron discharge device comprising an envelope, two chemically-sensitive electrodes spaced apart in the envelope, a partition transversely across. the envelope between the two electrodes and respectively spaced therefrom, said partition having an enlarged window formed therein through which the two electrodes can operatively interact, and a pair of semi-circular plate members re spectively pivotally mounted on said partition and abutting, one side thereof, said plate members forming a shutter and being respectively selectively movable in a plane parallelto the plane of said partition. across said opening to close the same, one. of said plate members having a batten attached to one edge thereof and overlying the corresponding edge of the other of said plate members when said plate members are moved to close said opening, thereby to close the crack between said plate members.

References Cited in the file of this patent UNITED STATES PATENTS 2,149,849 Lubszynski et al Mar. 7, 1939 2,283,413 Cashman May 19, 1942 2,455,381 Morton et al Dec. 7, 1948 2,455,868 Koch Dec. 7, 1948 2,462,921 Taylor Mar. 1, 1949

Images