US2143582A

US2143582A - Electron discharge tube

Info

Publication number: US2143582A
Application number: US189012A
Authority: US
Inventors: Schubert Georg; Knick Ulrich; Ruska Ernst
Original assignee: FIRM OF FERNSEH AG
Current assignee: FIRM OF FERNSEH AG
Priority date: 1937-02-04
Filing date: 1938-02-05
Publication date: 1939-01-10
Anticipated expiration: 1956-01-10

Description

Jan 10, 1939. G. SCHUBERT ET AL ,1 2

' ELECTRON DISCHARGE TUBE Filed Feb. 5, 1938 INVENTORS, GEO/PG SCHUBERT. ULRICH mwc/r.

BY ERA/S7 RUSK/4 W TORN s.

Patented Jan. 10, 1939 PATENT OFFIE ELECTRON DISCHARGE TUBE Georg Schubert,

Berlin- Zehlendorf,

Ulrich Knick, Steglitz, and Ernst Ruska, Spandau,

Germany, Aktiengesellschaft, Germany Application February In Germany 2 Claims.

It may be necessary to shield, in part or completely, individual electrodes or groups of electrodes in photoelectric multipliers for various, such as for instance electrical reasons. This,

however, complicates the forming of the tube because the screened-off electrodes are not soreadily accessible to oxygen or caesium as the unscreened electrodes, and the oxidation of the screened electrodes cannot be observed. Therefore, special tubulations for the introduction of caesium to such a screened-off group of electrodes must be provided for the forming, or the attempt must be made to maintain certain differences in temperature between the screened-off and the open electrodes. However, the disadvantage still remains that the degree of oxidation of the screened electrodes cannot be observed.

These defects may be overcome if the screening device is carried out according to the invention in such a manner that it may be opened and closed in vacuum. The forming may then take place when the screen is open, whereby all of the above-mentioned diificulties during the forming process are eliminated. After the process is completed screening is closed, while the tube is in an evacuated condition. The covering device can be operated, for instance, magnetically or by relieving the tension on a spring, for instance, by a fuse wire or bimetallic spring, or by inertia or gravity, respectively. It is preferable to provide such a locking device which may maintain the movable part in a fixed position for operation of the tube and which cannot be opened at all or only by the same means, as above mentioned. A further advantage of the device according to the invention is the possibility of measuring the photcsensitivity or secondary emission ratio after the forming of the tube by illumination or bombardment by electrons.

As an example, the application of the invention in an image analyzing tube with a stationary aperture and secondary emission amplification will be described. In the device according to Farnsworth illustrated in the drawing, the lens 6 projects an image of the object to be transmitted upon the photocathode l. The electron image thereby produced, and of which the current density distribution in space corresponds to the values of light intensity of the optical image, is scanned across the aperture 8 by means of deflection fields. The secondary emitting electrodes i of the electron multiplier aredisposed in a screened cylindrical metal housing 3-4 which is placed in the cylindrical tube diametrically in front of the window through which the assignors to Zehlendorf, near Berlin,

the firm of Fernseh 5, 1938, Serial No. 189,012 February 4, 1937 light falls. According to the invention, this metallic housing is interrupted by an aperture, leaving the electrodes free, and a movable tube 5 is provided which may be moved over the aperture of the screened cylinder by means of gravity after the tube is sealed from the pump and which tube is held in the aforementioned position indicated by the dotted lines in the drawing. In order to secure good electrical contact between the screened cylinder and the movable tube 5, the two; are connected by means of a thin flexible conductor 9. A guide it provides turning of the tube 5 while it is slid over the screened cylinder 3@ in order to bring an aperture II in the tube into such a position that it may serve as an aperture through which the photoelectrons enter into the cylinder 3-4. Upon striking the inner wall of that portion of the cylinder designed by reference numeral 3, such electrons as are refiected and such as may be secondarily emitted, will be attracted to the first electrode of the electron multiplier.

A screen provided with a movable portion may also be used to advantage in such cases where the forming of the surfaces is to take place in a screened-off space for certain reasons while the electrodes lie open during the operation of the tube. The above disadvantages may then be applied in an opposite manner.

We claim:

1. A cathode ray device comprising an envelope housing a photosensitive cathode at one end thereof, electron receiving means at the opposite end of said envelope, electron multiplier means comprising a plurality of secondary emissive electrodes and slidable hollow shielding means in alinement with said electrodes initially displaced therefrom to enable sensitizing said electrodes to render them secondary emissive and slidable over said electrodes to shield them against direct flow thereto of electrons from said cathode.

2. An electron discharge device comprising a cathode and a cooperating electron receiving means spaced therefrom, an electron multiplier having an electrode electronically exposed to said electron receiving means, a slidable hollow shield electrically connected to said electron receiving means and initially displaced from said electron multiplier electrode to enable sensitizing said electrode to render it secondary emissive and slidable over said electrode to thereafter limit the exposure of said electrode to said electron receiving means only.

GEORG SCHUBERT. ULRICH KNICK. ERNST RUSKA.