US3473070A - Glow-discharge tube containing a mixture of rare gases - Google Patents

Description

Oct. 14,1969

6- J.JM. AHSMANN ET AL GLOW-DISCHARGE TUBE CONTAINING A MIXTURE 0F R GASES Filed July 12, 1967 United States Patent M US. Cl. 313--210 3 Claims ABSTRACT OF THE DISCLOSURE A glow-discharge tube without a priming electrode and having as an ionizable medium a mixture of a light rare gas containing at least by volume of a heavier rare gas and less than 1% by volume of a third heavier rare gas or monatomic vapor having a higher ionization potential than that of the two rare gases and which forms no molecular ions therewith.

The invention relates to a glow-discharge tube without a priming electrode employing an ionizable medium consisting essentially of a light rare gas and a heavier rare gas, the quantity of heavier rare gas being at least 10% by volume of the quantity of light rare gas.

These mixtures are often used because of their low impedance at acoustic frequencies.

In such discharge tubes the restoring time is short, i.e., within a short time after the extinction of the discharge, the ignition voltage again reaches the original value. Although this is advantageous when such discharge tubes are used in many kinds of circuit arrangements, such a short restoring time may also have disadvantages. In glow-discharge diodes, for example, which are used in relaxation generators for electronic organs, the short restoring time is required to produce the maximum audible frequencies. However, it has been found that due to the quick recombination brought about by the short restoring time of the ionizable medium, the ionization of the tube vanishes completely after the extinction of the discharge, and so rapidly that at the minimum frequencies to be produced by such relaxation generators, disturbing variations occur in the ignition delay and hence in the instant of ignition. A priming electrode cannot be used inter alia in these circuit arrangements.

The invention has for an object to provide a glow-discharge tube employing an improved ionizable medium which obviates the aforesaid disadvantages.

In a glow-discharge tube without a priming electrode having an ionizable medium consisting essentially of a light rare gas and a heavier rare gas, the quantity of heavier rare gas being at least 10% by volume of the quantity of light rare gas, according to the invention, the ionizable medium also contains a third heavier rare gas or a mono-atomic vapor having a higher ionization voltage than that of the two rare gases in a quantity of at the most 1% by volume of the whole gas filling. This gas, or vapor, in the ionized state, furthermore, is incapable of forming molecular ions with the first or second rare gases. Due to the small concentration of the latter constituent it cannot form molecular ions either so that volume recombination of the ions of said constituent is not possible. After the extinction of the discharge in the tube, which discharge is effeced for the major part in ions of 3,473,070 Patented Oct. 14, 1969 the second and also of the first rare gas, these ions will disappear by the formation of molecular ions due to the high concentration of said gases. Thus, the restoring time is short, and moreover a rapid deionization takes place. The ions of the admixture according to the invention, however, disappear only slowly by diffusion into the wall because no molecular ions can be formed. Due to their presence, the residual ionization is sufiicient to permit re-ignition without the occurrence of disturbing variations in the ignition delay. However, the restoring time is not influenced by the low concentration of the residual ions so that at a higher discharge frequency, the discharge tube also does not ignite prematurely. Gas mixtures satisfying the requirements in accordance with the inven' tion are: neon containing 12% of argon and 0.5% of krypton, or instead of krypton, caesium-vapor at room temperature. During recombination of argon by Ar ions, metastable argon atoms are also formed which have a long life. When colliding with caesium atoms, they can form caesium ions so that the ionization can be maintained for a long time.

An additional advantage of the admixture in accordance with the invention is that in tubes without a priming electrode, the delay in ignition must be eliminated by means of a radio-acive composition. The required quantity of this composition is determined by the desired reduction of the ignition delay and by the properties of the ionizable medium. In known tubes, all the charge carriers present in the discharge can disappear by volume recombination, so that for a given strength of the radio-active composition, the ionization attains only a low intensity. In a tube according to the invention, however, the ions of the admixture formed by the radio-active composition will disappear slowly and will thus attain a higher concentration. Such a tube is described in application Ser. No. 648,743, filed June 26, 1967, and it has been found that, conditions being otherwise the same, a reduction of the strength of the composition by a factor 10 can be obtained. Thus, a very small quantity of radio-active material suflices for obtaining a smooth first ignition in tubes having a priming electrode.

The invention will be described with reference to the drawing, the sole figure of which shows in a partly de veloped perspective view a glow-discharge tube according to the invention.

The pin-shaped molybdenum cathode 1 having a diameter of 1 mm. is arranged coaxially in an anode 2 consisting of nickel gauze and having a diameter of 5 mm. The glass envelope 3 has an inner diameter of 5.5 mmr. The lead-in wires 4 and 5 are flexible. During preparation of the tube, a molybdenum deposit 6 is formed on the inner side of the bulb. The gas filling at a pressure of torr consists of neon containing 12% of argon and 0.5% of krypton.

On the base of the tube a dot of titanium 7 is provided in which tritium is absorbed and which has a strength of 0.5 c. Thus, when the tube is switched on, the delay in ignition is smaller than 1 m. per second. In? the gas filling does not contain krypton, this small delay can be achieved only with a strength of 5 ac. of the tritium composition.

With this gas filling, no disturbing jitter occurs even at the minimum frequency of approximately 40 c./s. which is produced by the tube in a relaxation circuit arrangement.

While the invention has been described with reference to particular embodiments and applications thereof, other modifications will be apparent to those skilled in this art without departing from the spirit and scope thereof as defined in the appended claims.

What is claimed:

1. A glow-discharge tube comprising an envelope containing a pair of electrodes and an ionizable medium consisting essentially of a light rare gas and a heavier rare gas, the quantity of heavier rare gas being at least 10% by volume of the quantity of light rare gas, and a constituent having a higher ionization voltage than that of the two rare gases in a quantilty of at the most 1% by volume hereof, said latter constituent in the ionized state, being incapable of forming molecular ions with the first and the second rare gases.

2. A glow-discharge tube as claimed in claim 1 in which the ionizable medium consists of neon, argon and krypton.

3. A glow-discharge tube as claimed in claim 1 in 15 4 which the ionizable medium consists of neon containing argon and caesium vapor at room temperature.

References Cited UNITED STATES PATENTS 2,056,662 10/1936 Foulke 313-210 X 2,507,696 5/1950 Depp 3l3210 X 2,800,600 7/1957 Drennan et al. 3l3225 X 10 JAMES W. LAWRENCE, Primary Examiner RAYMOND F. HOSSFELD, Assistant Examiner U.S. Cl. X.R. 3l3225, 226

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