US3648092A

US3648092A - Arsenic-antimony-bismuth hollow cathode lamp

Info

Publication number: US3648092A
Application number: US27697A
Authority: US
Inventors: James E Wooldridge; George K Yamasaki
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1970-04-13
Filing date: 1970-04-13
Publication date: 1972-03-07
Anticipated expiration: 1989-03-07

Abstract

A radiation source of the hollow cathode variety capable of emission of spectral radiation characteristic of the elements arsenic, antimony and bismuth.

Description

0 United States Patent [151 3,648,092 Wooldridge et al. 51 Mar. 7, 1972 [54] ARSENIC-ANTIMONY-BISMUTH HOLLOW CATHODE LAMP [56] f r n Ci [72] Inventors: James E. Wooldridge, Elmira Heights; UNITED STATES PATENTS Gems Yammki, Hmeheads, 3,361.925 1/1968 Vollmer ..313/209 x 3,412,278 11/1968 Sebensetal. ..3l3/346 [73] Assignee: Westinghouse Electric Corporation, Pitt- Sburgh, Primary ExaminerRaymond F. l-lossfeld Attorney-F. H. Henson and C. F. Renz 1221 Filed: Apr. 13, 1970 1211 Appl. No.2 27,697 [57] ABSTRACT A radiation source of the hollow cathode variety capable of 521 u.s.c1. ..3l3/209,3l3/2l8,3l3/346R jgfijgg" gf jff f figfigfggig' elements 511 1111.01 ..l-l01j6l/04 [58] Field of Search ..3l3/209, 218, 346 4 Claims, 1 Drawing Figure JLQ I l 2s 22 Patented March 7,1972 3,648,092

WITNESSES INVENTORS James E. wooldridge and George K. Yum oki BY// V fi ATTORNEY ARSENIC-ANTIMONY-BISMUTII HOLLOW CATI-IODE LAMP BACKGROUND OF THE INVENTION This invention relates to electron discharge devices of the hollow cathode type which are adapted for emitting radiation having defined spectral lines dependent upon the material within the cathode. One particular application of these light sources is in spectroscopic investigations. There have been considerable numbers of hollow cathode devices provided which both emit radiation of a single element or emit radiation of several elements from a common cathode. In the case of the element arsenic, the prior art practice was to place a lump of this element inside a cup-shaped cathode. The cup-shaped cathode was of a high-melting point material such as iron. It was also possible to machine a cathode from a pure slug of arsenic. While these cathodes did produce the spectral lines of the arsenic, they did exhibit several problems. The vapor pressure of arsenic is high and therefore the operating current of the device has to be kept at a low value. If this is not done, rapid destruction of the cathode could occur..It is also found that the spectral output, which is related to operational current, suffers because of the current limitation. The high-vapor pressure of arsenic at the operating temperature also causes excessive evaporation of the cathode material and its deposition on the internal structure of the lamp. This can cause electrical shorts or erratic discharges in the device after a few hours of operation. The cathode material also can vaporize and coat the surface of the output window of the lamp and thereby reduce the transmission of light through the window.

It is accordingly a general object of this invention to provide a new and improved hollow cathode for use in the spectral radiation device capable of emission of spectral lines of the particular elements arsenic, antimony and bismuth.

SUMMARY OF THE INVENTION A new and improved hollow cathode device comprising a cathode comprised of a metallic substance of arsenic, antimony and bismuth and in which the arsenic consists of about 25 to 75 percent by weight, the antimony about to 50 percent by weight and the bismuth less than 30 percent by weight of the metallic substance.

DESCRIPTION OF THE DRAWING For a better understanding of the invention, reference may be had to the preferred embodiment, exemplary of the invention, shown in the accompanying drawing which is a perspective view, partially broken away and partially in section of a discharge device embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing, there is shown an electron discharge device 10 in accordance with the present invention. The electron discharge device 10 includes an envelope 11, made of a suitable insulating material such as glass and having an enlarged tubular portion 12 and a smaller tubular portion 14 which are interconnected by a transition portion 13. The tubular portion 14 is sealed off at one end by a window 16 which is made of a suitable material such as U.V. glass, quartz, magnesium fluoride, lithium fluoride to name a few for efficiently transmitting radiation wavelengths produced by the device. The tubular portion 12 is sealed off by a button stem 18 with a tipped off exhaust tubulation 20 in a manner well known in the art. I

A cathode element 22 which is comprised of a metallic substance of arsenic, antimony and bismuth is provided within the envelope 11. The cathode element 22 is cup-shaped and may be of cylindrical configuration having a centrally extending opening of about one thirty-second to one half inch in diameter or hollow portion 24 extending from an edge 23 of the cathode element 22 facing the window 16' into the cathode element 22 for a length of about A; to 2 inches. The cathode element 22: may be supported by an electrically conductive lead 26 made up of suitable material such as nickel. The lead 26 may be affixed to the cathode element 22 and extends through the stem header 18 to the exterior of the envelope 11. The lead 26 provides not only the support for the cathode 22 but means of applying a potential to the cathode 22.

An anode element 28, which is illustrated as a ring member is positioned in close proximity to the cathode element 22 at its upper edge '23. The anode element 28 is made of a suitable electrically conductive material such as tantalum and is supported within the envelope by means of the 2 support leads 30. At least one of the support rods 30 is of an electrical conductive material such as nickel. The rods 30 are secured to the anode 28 and are supported and secured through the button stem 18. A' potential may be applied to one of the support rods 30 for application of potential to the anode.

In order to limit the path of electrical discharge between the cathode element 22 and the anode element 28, shielding means are provided which include two

insulating discs

38 and 44 which are disposed in a spaced parallel relationship between the cathode element 22 and the anode element 28. More specifically, the insulating disc 38 has an aperture 40 therein which is disposed concentrically about the hollow portion 24 of the cathode element 22. Further, the insulating disc 38 may be disposed so as to be in close proximity to or abut with the upper edge 23 of a cathode element 22 and extend therefrom to the inner surface of the envelope 1!. The second insulating disc 44 has an aperture 41 into which the cathode 22 is positioned and the disc 44 extends from the outer surface of the cathode 22 to the inner surface of the envelope 1]. In addition, the shielding means includes a pair of insulating sleeves 48 disposed about the support rods 30 and extending between the button stem 18 and the insulating disc 44. Insulating rings 47 are disposed about the support rods 30 between the

insulating discs

44 and 38 and insulating rings 46 are disposed about the rods 30 between the insulating disc 38 and the anode element 28. A more detailed description of the structure may be found in US. Pat. No. 3,264,5ll entitled Low-Discharge Device by G. K. Yamasaki.

The envelope 11 is exhausted and a suitable gas such as argon or neon is provided therein at a pressure of about 1 mm. of Hg. to 30 mm. of Hg.

In the operation of the device, suitable potentials are applied between the cathode 22 and the anode 28 so that an electrical discharge occurs between the cathode element 22 and the anode element 28 through the gaseous medium within the envelope 11. This discharge creates positive ions of gas which in turn'bombard the inner surface of their opening 24 of the cathode element 22 thereby sputtering excited atoms of the three materials off of the walls of the opening 24. These excited atoms emit light of wavelengths characteristic of three materials, namely arsenic, antimony and bismuth. This light is emitted through the window 16.

A method of manufacturing the cathode element 22 may be as followsi The starting materials for the constituents may have a purity of about 99.99 percent and approximately 4 to +20 mesh size. One specific combination of materials for the cathode element 22 consists of 40 percent arsenic, 40 percent antimony and 20 percent bismuth by weight. The materials are weighed out in the above ratio and intimately mixed together and then may be placed in a vycor bulb of approximately eleven thirty-second inches inside diameter and about 6 inches long. The bulb may then be evacuated to about 10 torr and sealed off. The bulb must be under a negative pressure because of the high-vapor pressure of molten arsenic. This vapor pressure is gradually reduced as the arsenic reacts with the antimony and bismuth. After the bulb has been sealed off, it is placed in a furnace and heated to about 300 C. and held there for 15 minutes. It is then taken to a temperature of about 600 and held for 15 minutes and then to about 800 C. for 30 minutes. The material is completely molten at about 650 to 700 C. In order to help mix the constituents, the furnace may be slowly rocked during the 30 minute period at the temperature of 800 C. The additional heat is to ensure that the mixture is in a molten state. After completion of the heating cycle the furnace is cooled down at a rate of about 2 per minute and the resulting metallic substance is cast into a solid rod when it is cooled. The vycor tubing may be broken away and the rod machined into the cathode element 22.

[t has been found that for practical reasons the arsenic must be 25 to 75 percent by weight, the antimony to 50 percent by weight and the bismuth less than 30 percent by weight of the metallic substance. The addition of antimony primarily determines the operational current of the device by having the effect of lowering the effective vapor pressure of the arsenic in the metallic substance. It also effectively decreases the electrical resistance of the cathode. One is then able to operate at higher currents without excessive vaporization of the arsenic. For example, operational currents of milliamperes have been utilized for a period of 900 hours time without destruction of the cathode. The addition of bismuth is to primarily improve the machinability of a cathode and to reduce the drift in the arsenic spectral output with respect to operational time of the cathode.

It will therefore, be apparent that there has been disclosed a hollow cathode discharge device comprised of a cathode which will generate spectral emission representative of the three elements arsenic, antimony and bismuth. The wavelengths of emission of most common interest and use are Asl,937A. and 1,972A., Sb-2,068A., 2,311A. and

Bi2,230A., 3,068A.

We claim as our invention:

1. A radiation source of the hollow cathode type comprising an anode and a cathode positioned within an envelope with a gas filling, said cathode including a metallic substance of arsenic, antimony and bismuth from which spectral emission characteristic of arsenic, antimony and bismuth is desired, said metallic substance comprised of about 40 percent by weight of arsenic, about 40 percent by weight of antimony and about 20 percent by weight of bismuth.

2. The radiation source of claim 1 in which said cathode is a cup-shaped member consisting essentially of said metallic substance.

3. A radiation source of the hollow cathode type comprising an anode and a cathode positioned within an envelope with a gas filling, said cathode including a metallic substance consisting essentially of arsenic, antimony and bismuth from which spectral emission characteristic of arsenic, antimony and bismuth is desired, said metallic substance consisting essentially of about 25 to 75 percent by weight of arsenic, about 15 to 50 percent by weight of antimony, and less than about 30 percent by weight of bismuth.

4. The radiation source of claim 3 in which said cathode is a cup-shaped member consisting essentially of said metallic substance.

Claims

2. The radiation source of claim 1 in which said cathode is a cup-shaped member consisting essentially of said metallic substance.
3. A radiation source of the hollow cathode type comprising an anode and a cathode positioned within an envelope with a gas filling, said cathode including a metallic substance consisting essentially of arsenic, antimony and bismuth from which spectral emission characteristic of arsenic, antimony and bismuth is desired, said metallic substance consisting essentially of about 25 to 75 percent by weight of arsenic, about 15 to 50 percent by weight of antimony, and less than about 30 percent by weight of bismuth.
4. The radiation source of claim 3 in which said cathode is a cup-shaped member coNsisting essentially of said metallic substance.