US2881343A - Electron multipliers - Google Patents

Description

Apnl 7, 1959 J. J. PoLKosKY ET AL 2,881,343

' ELECTRON MULTIPLIERS Filed April 1e. 1957 INVENTORS JDSEPH J. PDLKDSKYE- AUGUST M. SPLINTER United btates Patent ELECTRON MULTIPLIERS Joseph J. Polkosky and August M. Splinter, Lancaster,

Pa., assignors to Radio 4Corporation of America, a corporation of Delaware Application April 16, 1957, Serial No. 653,204

4 Claims. (Cl. 313-104) This invention relates to the art of making secondary electron-emitting electrodes and electron multiplier tubes containing the same.

In low-voltage, high gain electron multipliers (e.g. photomultipliers, used as scintillation counters, headlight dimmers, etc.) it is usual to employ dynodes made of nickel.

The principal object of the present invention is to provide an improved nickel dynode, and one characterized by its stability, long life and the uniformity of its electron emission over its surface.

The foregoing and related objects are achieved in accordance with the invention by subjecting the target surface of a nickel dynode, or assembly of dynodes, to an oxidation process and subsequently depositing antimony and cesium on the nickel oxide.

The invention is described in greater detail by reference to the drawing wherein:

Fig. 1 is an elevational view, partly in section of -a photomultiplier embodying the invention; and,

Fig. 2 is a ow chart of the method of the invention.

The principles of the invention may be employed to prepare an electron multiplier tube of the type known as the RCA 6655 photomultiplier. Such a tube is shown in Fig. 1 and includes a tubular glass envelope 12 having a transparent face plate 14 at one end on which is formed an electron-emissive layer or photocathode 16 adapted to emit electrons when exposed to light. The photocathode 16 may be of the alikali-antimony type or of any other suitable type and may be formed by evaporation of suitable substances onto the surface of the face plate 14. A conductive lm 18 of aluminum, silver or the like, extends along the inner wall of the envelope 12 from the photocathode 16 toward the opposite end of the envelope and serves to allow electrical contact to be made to the photocathode.

Spaced from the photocathode 16 is an apertured disk electrode 20 which may be employed as a focusing or accelerating electrode for electrons emitted by the photocathode. An electron multiplier assembly 22, comprising a plurality of secondary electron emitting electrodes or dynodes 24, is mounted directly behind the disk electrode 20 in such a position as to receive photoelectrons passing therethrough. The electron multiplier assembly 22 may be one of the type shown in U. S. Patent 2,285,126 of Rajchman et al. The electrical constituents of the tube 10 are suitably connected to electrical leads 26 which extend through a glass press 27 which is sealed to the balance of the envelope. The press 27 includes an exhaust tubulation 29. The materials from which the photocathode is prepared are provided within the envelope in suitable form and suitably supported for evaporation onto the face plate of the envelope. Such materials may be provided as pellets 28 and 30 mounted on suitable heatable wires 32 and 34 or the like secured to the apertured disk and facing the face plate 14. A metal container 36 suitable for carrying materials from which cesi- Patented Apr. 7, 1959 ice um vapor may be obtained is suitably mounted within the tube, for example on one of the leads 26.

The dynodes 24 of the electron multiplier assembly 22 are made of nickel and in preparing the multiplier assembly the dynodes are cut from a suitable strip of nickel and are suitably formed, shaped and cleaned. The dynodes thus assembled are then placed in a suitable container and vacuum baked in an oven at a temperature in the range of 800 C. to 900 C. for a time of the order of 15 to 40 minutes. This operation is performed to degas the dynode assembly and, ordinarily, baking for about one-half an hour at 800 C. is satisfactory. Next, oxygen is admitted to the oven at a pressure of about one inch of mercury and baking is continued at about 800 C. for about one minute. This operation provides a coating of nickel oxide on the dynodes.

The electron multiplier assembly, having oxidized nickel dynodes, is then removed from the oven but is maintained in the oxygen atmosphere and allowed to cool to room temperature. When the assembly has cooled to room temperature, a layer of antimony is formed by evaporation on the nickel oxide surfaces of the dynodes according to conventional practice.

T he dynodes are then assembled to form the multiplier assembly 22 having dynodes of nickel oxide coated with antimony. The multiplier assembly is then mounted on the press 27 and the press is sealed to the tube envelope 12. The envelope is evacuated, the photocathode 16 is prepared in known fashion and then the tube is baked to degas all parts. Baking for one-half to two hours at a temperature in the range of 300 C. to 400 C. is satisfactory. Finally, vapor of an alkali metal, such as cesium, is released in the envelope from the container 36, which is heated by induced radio frequency currents. The cesium vapor reacting with the dynode surfaces completes their activation.

Electron multi-pliers having dynodes made of nickel and processed according to the invention have been found to provide output currents or gains of the order of 3000 microamperes with 10-5 lumens of light on the photocathode and with volts applied to each dynode.

What is claimed is:

l. An electron multiplier electrode comprising a base vof nickel, a coating of nickel oxide on said base, and antimony and an alkali metal present on said nickel oxide coating.

2. An electron multiplier electrode comprising a base of nickel having a coating of nickel oxide, said nickel oxide coating including reaction products of antimony and an alkali metal.

3. An electron multiplier electrode comprising a base of nickel having a coating of nickel oxide, said nickel oxide coating including reaction products of antimony and cesium.

4. An electron multiplier tube comprising an envelope and containing an electron multiplier assembly made up of electron multiplier electrodes comprising a nickel ox ide layer on a base of nickel, said nickel oxide layer containing reaction products of antimony and cesium.

References Cited in the tile of this patent UNITED STATES PATENTS 2,620,287 Bramley Dec. 2, 1952 FOREIGN PATENTS 58,988 Denmark Aug. 18, 1941 OTHER REFERENCES Physics and Applications of Secondary Electron Emission, Bruining, McGraw-Hill, 1954, QC 721 B86.

Claims (1)

1. AN ELECTRON MULTIPLIER ELECTRODE COMPRISING A BASE OF NICKEL, A COATING OF NICKEL OXIDE ON SAID BASE, AND ANTIMONY AND AN ALKALI METAL PRESENT ON SAID NICKEL OXIDE COATING.

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