US2804573A

US2804573A - Gas discharge devices

Info

Publication number: US2804573A
Application number: US405374A
Authority: US
Inventors: William J Arrol; Jefferson Sidney
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-01-21
Filing date: 1954-01-21
Publication date: 1957-08-27
Anticipated expiration: 1974-08-27

Description

1957 w. J. ARROL ETAL GAS DISCHARGE DEVICES Filed Jan. '21, 1954 "Iillir'illlll INVENTORS MAL/FM WIWOL,

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1' ATTORNEY United States Patent 6 GAS DISCHARGE DEVICES William J. Arm] and Sidney Jefferson, Abingdon, England, assignors, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Application January 21, 1954, Serial No. 405,374

3 Claims. (Cl. 315-54) This invention relates to gas discharge devices such as cold cathode tubes.

An object of the invention is to provide a gas discharge device having a high dark current and/or stable striking voltage.

When tritium gas is counted in a Geiger-Muller tube filled in the normal way with argon and alcohol, very extensive radioactive contamination of the glass walls of the tube occurs. The contamination is not removed by heating to 150 C. and pumping off. It can therefore be assumed that the tritium is attached chemically in some Way to the glass and it may be present in hydroxyl groups attached directly to silicon atoms.

According to the present invention tritium gas is introduced into the envelope of a gas discharge device. As a gas the tritium is etfective as a low energy beta emitter calculated to increase the dark current and stabilise the striking voltage. An electrical discharge in the gas results in tritium becoming fixed in the surface of the envelope or other solid parts of the device where it is particularly eifective for the purpose of the invention. It is believed that the discharge dissociates the tritium and that atomic tritium is fixed in the surface. The drawing discloses a sectional view of a diode tube with tritium therein.

Two methods in accordance with the invention by which tritium may be introduced into a gas discharge device will now be described by way of example in connection with the manufacture of cold cathode tubes.

A cold cathode tube 1 with electrodes 2 and 3 in position ready for normal filling is firstly filled with tritium 4 or hydrogen gas containing tritium of an activity of about 100 micro curies at about a quarter of an atmosphere and an electrodeless discharge is then initiated by means of a high voltage, high frequency, electrode such as the point of .a Tesla coil placed near the wall of the tube. Alternatively, the point of the Tesla coil may be placed in contact with the lead-in wire of one of the electrodes of the tube. Enough tritium for the purpose of the invention goes down on the wall or on the electrodes as the result of the discharge. The remaining tritium is then pumped oil and the normal process of manufacture is proceeded with.

The amount of tritium fixed in any part of the internal surface of the tube can be influenced to some extent by localising the electrodeless discharge as by placing the point of the Tesla coil at a selected position outside the tube. The maximum amount of tritium is therefore arranged to be fixed in a position nearest and exposed to the discharge gap or gaps of the tube.

2,804,573 Patented Aug. 27, 1957 In the second method, tritium is mixed with the gases normally used to fill the envelope. The tritium may be diluted with hydrogen according to the amount of hydrogen the particular type of tube is able to tolerate. If a gettering process is to be used the tritium is then fixed in the solid elements of the tube before gettering, as in the previous example. In some types of cold cathode tube, however, no gettering process is used in which case the initial discharge to fix the tritium may be dispensed with since the tritium is almost equally effective either in the gaseous form or in combination with the solid elements of the tube.

During the operation of the tube there will, of course, be discharge and this will effect fixation of the tritium.

The process of the invention produces a device the inside walls of which emit, with a half-life of 11 years, a continuous stream of very low energy beta particles calculated to increase the dark current and stabilise the striking voltage of the device without involving an appreciable health hazard for the manufacturer or user.

The use of tritium has the advantage over the use of other radioactive substances in that, being a pure beta emitter, no activity penetrates the envelope of the tube and no health hazard arises when large numbers of the tubes are stored in bulk.

In the manufacture of tubes by the first of the above methods no health hazard arises since the tritium remains confined. In the second method, a precaution is necessary with normal filling machines to ensure that the header vessel, from which each batch of tubes is filled with gas, is not vented into the machine shop, after the tubes are sealed-ofi, as is the usual practice when inert gases are used.

We claim:

1. A method of manufacturing a gas discharge device comprising the steps of evacuating the envelope of the device, introducing tritium gas into said envelope, producing an electrical discharge in the tritium gas whereby tritium is chemically fixed to 'a surface Within the device, pumping off the remaining tritium gas and filling the envelope with a known gas filling.

2. A method of manufacturing a gas discharge device comprising the steps of introducing tritium into the envelope of the device, producing an electrodeless discharge in the tritium gas by means of a high voltage, high frequency electrode placed adjacent the outside of the envelope of the device, causing tritium to be chemically fixed to the inner surface within the device nearest the discharge and evacuating the remaining tritium and filling the tube with known gas fillings.

3. A gas discharge device comprising an envelope, at least an anode and cathode within said envelope, a coating of tritium chemically fixd to the inner surface of said envelope, said coating being at least over an area exposed to the discharge gap of the device, and a gas filling within said envelope.

References Cited in the file of this patent UNITED STATES PATENTS 2,374,677 Goldstein et a1. May 1, 1945 2,449,961 Treece et al. Sept. 21, 1948 2,576,100 Brown Nov. 27, 1951 2,652,510 Landrewy et a1. Sept. 15, 1953 2,669,609 Linder Feb. 16, 1954

Claims

3. A GAS DISCHARGE DEVICE COMPRISING AN ENVELOPE, AT LEAST AN ANODE AND CATHODE WITHIN SAID ENVELOPE, A COAT ING OF TRITIUM CHEMICALLY FIXED TO THE INNER SURFACE OF SAID ENVELOPE, SAID COATING BEING AT LEAST OVER AN AREA