US2811660A

US2811660A - Ion chamber amplifier tube

Info

Publication number: US2811660A
Application number: US369798A
Authority: US
Inventors: Norman H Lehrer
Original assignee: Tung Sol Electric Inc
Current assignee: Tung Sol Electric Inc
Priority date: 1953-07-23
Filing date: 1953-07-23
Publication date: 1957-10-29
Anticipated expiration: 1974-10-29

Description

Oct. 29, 1957 N. H. LEHRER ION CHAMBER AMPLIFIER TUBE Filed July 25, 1953 I I I l FIG. 5

-2'o -|'o v o +l'0' +20 GRID VOLTAGE R E R H E L H N A M R O N INVENTOR ATTORNEY United States Patent 2,811,660 ION CHAB/HBERAMPLIFIER TUBE Norman H. Lehrer, Bloomfield, N. J., assignor, by mesne assignments, to Tung-Sol Electric Inc., Newark, N. 1., a corporation of Delaware Application July 23, 1953, Serial No. 369,798

4 Claims. (Cl. 313-54) This invention relates to a gaseous conduction device having three or more electrodes that may be used as an amplifier or oscillator. It has particular reference to gas-filled devices that containv a quantity of radioactive material which causes continuous ionization within the envelope, thereby permitting current to flow between the electrodes under application of electrical potentials.

Prior .art discharge devices may be limited by one or more disadvantages such as, requiring a filament or heater supply, long stabilization time, minimum operating voltage, and high input power. Other disadvantages may include low amplification and loss of control by the grid electrode once conduction has been established between the cathode and the anode.

Discharge tubes constructed and operated in accordance with the present invention do not conduct electricity between electrodes during the condition which is commonly called glow or are discharge. The tubes are operated at voltages which are always less than the value which causes. a glow discharge. Ionization of the gas molecules is caused only by the radiation from the radium or other radioactive material within the envelope. The pressure in the envelope is high enough to prevent ionization by collision with the ionized particles and the potentials used are low enough so that electron field emission and corona discharge cannot occur.

One of the objects of this invention is to provide an improved gaseous conduction device which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to provide a gaseous conduction device which does not require a heated cathode.

Another object of this invention is to provide a gaseous conduction device which can be operated at low voltages and therefore be used in circuits which transmits small amounts of electrical power.

Another object of the invention is to so arrange the ionizing material within the envelope so that the input impedance of the tube is increased inany times over prior art tubes of similar design.

The invention comprises a gaseous conduction device having three or more electrodes. A constant source of ionization, such as radium, is mounted within the envelope so as to direct the penetrating radiation toward a restricted space. A control electrode is mounted between an anode and a cathode beyond the limits of the restricted space for controlling the amount of current which passes between the anode and cathode.

For a better understanding of the present invention together with other and further objects, thereof, reference is made to the following description taken in connection with the accompanying drawings.

Fig. 1 is a side view of an amplifier tube with some of the parts in section.

Fig. 2 is a cross sectional view ofthe tube shown in Fig. 1 taken along line 2-2 of that figure.

Fig. 3 is a schematic diagram of connections indicating one of the methods of connecting the amplifier tube shown in Fig. 1. I

Figs. 4 and 5 are graphs to illustrate the electrical characteristics of a specific example which has been constructed in accordance with the details described herein.

Fig. 6 is a cross sectional view of part of an amplifier tube somewhat similar to Fig. 1 but showing an alternate arrangement of parts, specifically the arrangement of the mounting which holds the radioactive material.

Referring now to Figs. 1, 2, an envelope l0 encloses the tube components in a gas tight container. These components include a cylindrical cathode 11, a rod-like anode 12, a control electrode 13, and a support 14 for a small quantity of radioactive material which is placed only on the outside surface of the electrode. This construction may also include

insulating spacers

15 and 16, although this form of construction is not necessary. A base 17 with pins 18 is used for convenient application to an external circuit.

The envelope lltl is filled with a dry gas such as nitrogen -or air at a pressure of about 700 mm. of mercury but this pressure may vary considerably to a value as high as 5 atmospheres or as low as 300 mm. of mercury. It has been found by experiment that the best results areobtained when a salt of radium such as radium sulphate or radium bromide is used. It is well known that radiations from any radium compound include a considerable percentage of alpha particles which have intense ionizing properties. It is also common practice to embed the radium material under a very thin coating of gold. This arrangement permits the ionizing radiation to pass through the film but retains the poisonous gas Radon from escaping into the air and poisoning workmen during the assembly process. Other radiation sources may be used instead of radium, such as radioactive cobalt.

The support 14 is made of a material whose density and thickness is sufiicient to absorb the radiations which might otherwise pass to the central part of the tube. For this reason the alpha particles and other ionizing radiations will be confined to that region in the tube which is between the cathode and the support 14.

When the tube is in operation a layer of ionized gas particles is adjacent to the inner cathode surface while the interior or central portion of the tube where the grid control electrode and the anode are positioned is relatively free of ionized particles and for this reason any potential applied between the control electrode 13 and the cathode 11 will produce very little current and this portion of the tube circuit therefore possess a high impedance. Other amplifier tubes somewhat similar to this arrangement have been proposed. One such design is described in a patent application by Wilber L. Meier, filed May 11, 1953, Serial No. 354,218, and a variation of this design is disclosed in a second application by Wilber L. Meier, Serial No. 354,219, filed May 11, 1953. in these tubes the radioactive material is placed in such a manner as to cause ionization throughout the interior of the tube volume and for this reason the impedance between the control electrode and the cathode is low and the input circuit to the tube when used as an amplifier takes considerable current, thereby reducing the available voltage amplification. The present tube restricts the gas ionization to portions adjacent to the cathode surface and in so doing the input impedance of the tube is raised more than 20 times above the impedance of a tube which contains gas ionization throughout its entire volume.

Fig. 3 indicates the manner in which the amplifier tube should be connected as a voltage amplifier, the input circuit comprising connections to the control electrode 13 and the cathode 11. A biasing circuit with a source of potential 2% and a resistor 21 is connected between the control electrode and the cathode as in other varieties of amplifier circuits. The output circuit of the amplifier may be derived from a connection to the cathode 11 and the anode 12 although other forms of output circuits can be used. An anode source of potential 22 and an anode impedance 23 may be employed in the usual manner to keep the anode at an:average positive potential. The support 14 for the radioactive material may be a nonconductor such as mica or a ceramic composition but it is usually more convenient to use a metal support and if this is done a lead-in conductor is attached to the support and connected to one of the pins 18. This pin may then be connected to a part of the anode supply circuit and given a positive voltage which may vary with the requirements of the circuit and its application. This connection is indicated in Fig. 3 by a dotted line 24.

Figs. 4 and 5 indicate the relationship between the grid voltage and the anode current in one case and the grid voltage and the grid current in the second case. It should be noted that these curves show a marked similarity to the curves which represent the performance of well known triodes used in amplifier circuits.

Fig. 6 shows an alternate arrangement of parts and includes an envelope 10, a cathodell, an anode .12, and a control electrode 13. The support 14 for the radioactive material in this case is a helix which is wound around the outside of the control electrode and which has radioactive material only on its outside surface. Other variations of the radioactive material support will be obvious and may consist of a plurality of rings each similar to the one shown in Fig. 1 or the supports may be arranged in a vertical alignment, still surrounding the control electrode and containing radioactive material only on the sur- 1 face which faces the cathode 11.

The above description has included only that type of conduction device in which the ionization was restricted to a region adjacent to the cathode. These devices work equally well when the ionization is restricted to a region adjacent to the anode and excluding the control electrode.

Since the envelope contains a quantity of negative electrons and positive ions the applied potentials may be reversed and the anode and cathode interchanged.

While there have been described and illustrated specific embodiments of the invention, it will be obvious that various changes and modifications can be made therein without departing from the field of the invention which should be limited only by the scope of the appended claims.

I claim: 7

1. A gaseous conduction device comprising; an envelope filled with ionizable gas; an anode, a cathode, and a control electrode mounted within the envelope; a shield mounted between the control electrode and the cathode;

and a radioactive material secured to said shield so that ionizing radiation is directed toward the space adjacent to the cathode while shielding the anode and control electrode from said radiation and preventing radioactive ionization in the space between the anode and the control electrode.

2. A gaseous conduction device comprising; an envelope filled with ionizable gas; an anode, a cathode and a control electrode mounted within the envelope; each of said electrodes having a lead-in conductor for connection to an external circuit; said control electrode positioned between the anode and cathode for altering the electric field between them; a metal shield mounted between the control electrode and the cathode; and a radioactive material secured to said shield so that ionizing radiation is directed toward the space adjacent to the cathode while shielding the anode and control electrode from said radiation and preventing radioactive ionization in the space between the anode and the control electrode.

3. A gaseous conduction device having a plurality of electrodes comprising; an envelope filled with an ionizable gas; said electrodes including an axial anode, a cylindrical cathode, and a control electrode; a helical support mounted within the envelope between the control electrode and the cylindrical cathode; and a quantity of radioactive material secured to said helical support, on the side facing the cathode, for causing gas ionization in a restricted space adjacent to the cathode surface while shielding the anode and the control electrode from said radiation.

4. A gaseous conduction device comprising; an envelope filled with ionizable gas at a pressure of more than 30 cm. of mercury; an anode, a cathode, and a control electrode mounted within the envelope; each of said electrodes having a lead-in conductor for connection to an external circuit; a metal shield mounted between the control electrode and the cathode; and a radioactive material secured to said shield so that ionizing radiation is directed toward the space adjacent to the cathode while shielding the anode and control electrode from said radiation and preventing radioactive ionization in the space between the anode and the control electrode.

References Cited in the file of this patent UNITED STATES PATENTS 1,145,735 Ainsworth July 6, 1915 2,032,545 McElrath Mar. 3, 1936 2,266,665 Summers Dec. 16, 1941 2,652,510 Landrey et al Sept. 15, 1953 2,728,004 Victoreen Dec. 20, 1955