US2892967A - Ionic discharge tubes - Google Patents

Description

June 30, 1959 J. M. N. HANLET IONIC DISCHARGE TUBES Filed 001:. 28, 1957 IONIC DISCHARGE TUBES Til Jacques Marie'NoEl Hanlet, Paris, ,France,.assignor to Centre dEtudes et ..de Developpements .de lElectronique,CEDEL, Pai'is',"Fr"ance Application October 28, 1957, Serial No. 692,605

14 Claims. (Cl.= 315- 168) The present inventionrelates-to improvementsin-the design of gas or vapour-filled discharge -tubes-which operate by the generation and maintenance of a plasma between a pair of electrodes; anode and cathode, mounted' within a sealed bulb containing the said'gas or vapour atmosphere. relating to that spatial part of a gas or vapour atmosphere wherein these exists a high 'andsubstantially equal concentration of positive and negative charges,'viz.--of free electrons and ions;

It more partioularlyrelates to those of: such tubes which include between the said cathode andthe said anode, a control grid-electrodeenabling to modul-ate--.

the said plasma and *the anode'current of which is consequently controlled from a so-called alternating 1 signal (which may have the waveform of a sine wave-or a saw-toothed or square wave or-any other similar waveform) of from a DC. signal, theamplitude-of which varies in a continuous fashion.

The initiation and maintenance 'ofthe-discharge in such tubes have been obtaineduntil now by applying between across anode and cathode thereoffl- Suchan'energyconsumption wasfurther increasedfrom the fact that it was most commonly needed to incorporate =thereinthernrionic cathodes for obtaining the required-current deliveries therefrom. .From a further point of view,-and still with- 1 respect to that need of a-high potential difference between anode. and cathode thereof, the so-called: miniaturizing process could not easily .be applied to such tubes as this implied drastic conditionsfor the heat dissipa- 1 tion therefrom. Such a set of drawbacks and limitations had led to a restrict-ionin the use ofsuch tubes. whereas,.. on the other hand, they-present a definite interest intthat they are useful and advantageous current .amplifierszx 1 the plasma thereof, which is electrically. neutral, .iszia.

quite good conductor, as is well known, andconsequenp. 1y presents a low resistivity, it is .then adapted .to support currents of high intensity suitable for such a high gain current amplification process. .1

According to the present invention, the initiation and maintenance of the plasma insuehtubes ash'erein above specified are obtained from the incorporation. to the structure thereof ofv a beta-particle emitter. The radia-.

tion of particles, from... the .saidwemitter then. produces: 1 from collisions f-.the. saidparticleswiththe. molecules. of the gas atmosphere within the-bulb a permanent ioniza-= t tion of the said atmosphere, though only a quite reduced potential difference is applied across the-cathode and P anode thereof, much lower than-that -which would have--- Patent f w Claims priority, application France November 30, 1956' i been needed for producing theinonization of .the said atmosphere. aThepotential differenceiapplied across the cathode and anode of a discharge tube according to the,

invention could not either initiate or maintain by itself this plasma exists, for enabling thecirculation there, through of a high intensity current which may be picked up in the anode circuit of the said tubefrom which a applied toria control grid inserted between the anode and cathode of the said tube.

of electrons emitted from the cathode and which reach the anodeofthe tube.

the electronemissive layer of the cathode, or on a plurality of rods evenly distributed around the cathode and in close proximity thereof. Such an arrangement avoids the necessity of any screen for the bulb against the action as theaction of the beta particles therefor adds to that trons fromthe said cathode. Consequently, a'discharge tube according to the invention may be made with a no'n-th-ermionicbut coldcathode.

'For further disclosing the features of the invention,

H reference will be made'to the single figureof the accompartying drawing Of course such technologicaldetails as seals and spacers are not shown and will not. be retechniques. The bulb of the tube, which may be considered as f' v z. an anode 2, a control grid- 3 and a cathode the emiswhich emits beta particles,,viz. a radio-isotope.

layer of carbonates and/or nitrates and/0r oxides of 'instance,"which only aifects in a practically negligible the metal may foriinstance'be of about 25 microns. This 5flayer 6 may have been obtained in any suitable way. and

for instance from 'a heat evaporation process, a "chemical reaction of aradio-iSOtope salt'or a precipitation or. sedimentation thereof. The radio-isotope material is fj chosen amongst those which emit a beta ray for taking 6 5 that this :periodreaches or exceeds that of the useful life contemplated for the concerned'discharge tube (such a-usei ul life'is mainly defined bythat of the cathode femissive'layer and/or the reduction'of the atmosphere pressurewiththe time); It is: not necessary to have re Patented June 30,1959 7 the plasma in the said atmosphere but it suflices, as

load is fed,..and-this.current is controlled-by the signal The action of, such a signal is quite conventional per se, acting on the, number In a preferred embodiment of the. invention, .all 'elec- T trodes of the tube'are made coaxial andthe beta particle "emitter is provided as 'a film deposit either. on. the internal surface of a hollow red the outer surface of which bears 'ofthe betaparticles, as the anode of the tube may be m-ade of a suitable material therefor, and further it in creases the electron emission from the the cathode layer of the ions of the gas atmosphere for extracting elecferred to, as being apparent from the conventional cylindrical is shown at 1 and contains agas atmosphere. reduced therein afterthe mounting of the electrodes,.,..

si've layer of which 4 is formed over the outer face. of I athin hollow cylinder 5, over the inner face of which" has been formed a thin layer' or film,of"a material A The emissive layer of the cathode may consist of a ch elements. as barium, "strontium or any othenelements known to produce a substantially high number of 7 electrons when activated. This layer may be formed over a very thin cylinder of a metal such as-nickel for way the passing therethrough of the beta particles from J i the film .6' on the inner face thereof. The thickness of advantageof' the fact that'such-a kind of radiation has only a small penetration power and consequently does not necessitate stressing conditionsfor the handlingthere= of. It is of course apparent that the said radio-isotope material must have a confv'enientlylengthy .period so course tosuch radio-isotopes the useful life of which er 'ceed-s several -yearsthrough otherconsiderations-and' h mainly economical-ones may leadte usesome-isotope concerns isotopes of lengthy useful life but of acceptable price, one may cite the Carbon 14 the life of which is equal to 5400 years.

From the point of view of the specific activity which is required from a radio-isotope as used in a tube according to the invention, it may be noted that in a design of such. a tube and for a predetermined geometry of the electrode structure thereof, one may base the estimation on the evaluation of the number of ions produced within the gas atmosphere by the beta particles. Such an evaluation takes into account the following factors: energy of the isotope, expressed in electron-volts, weight of the said isotope in the structure, intrinsic characteristics of the gaseousatmosphere (diameter of the molecules of the gas and capture section thereof), and conditions imposed to the said atmosphere (number of molecules per cubic centimeter, according to the pressure and temperature thereof, volume of the bulb).

The choice of the gas defines, at some extent at least, the potential difference value to be applied across the cathode and anode of the tube for the utilization thereof, viz., the E.M.F. value of the battery 7 connected across the said electrodes. When helium or neon is used, the potential difference may be lower than 24 volts. For hydrogen, nitrogen, argon, krypton or xenon, this potential differenee may remain lower than 12 volts. For a metallic vapour, suchas quicksilver, cadmium or other, that potential difference may remain lower than 6 volts.

The possibility of using a cold cathode for the major part of the possible uses of such a discharge tube is mainly due to the fact that the beta particles themselves produce the extraction from the electron emitting layer of the cathode (and at a lesser degree of secondary electrons from the grid and anode material) of a substantial number of electrons; the action of the said particles adds to that of the ions which normally ensure such an extraction from the said cathode. Of course for high power discharge tubes, it will be possible to have recourse to thermionic cathodes in order to increase the volume and density of the plasma and consequently the average value of controllable power from the tube. 2 Nothing impedes in such a case that the heater filament for the thermionic cathode receives part at least of the beta particle emitter material.

On the other hand, it must be emphasized that as much as possible the beta particle emitter material must be protectedagainst impact of ions onto it. Such a condition apparently is satisfied in the shown structure of discharge tube. When, for technological purposes, the location of the emitter within the cathode cylinder could not be maintained, the radio-isotope could then be deposited over thin rods evenly arranged around the cathode and preferably within the black space around the said cathode in the plasma atmosphere, and each film of isotope would be protected by a shield or screen from the impact of ions from the plasma, such a shield consisting for instance of a nickel cylinder of some tens of microns of thickness thereof.

For arranging a gas discharge tube according to the invention as a signal amplifier, a battery voltage is also applied across the cathode and control grid thereof, for instance from a battery shown at 10 in the drawing. The control grid is negatively biased with respect to the cathode and the input control signal may then be applied across the input terminals 12 which are terminals of a series-connected impedance member 11, for instance a mere resistor. The amplified signal may be collected across a load impedance 8, serially connected into the cathodeto anode circuit. The output terminals toward any utilization equipment are shown at 9. For an A.C. input signal, the impedance 8 may consist of the cathode having an electron emissive layer, an anode and a control electrode within a single envelope and a radioactive. particle emitter in cooperative association with the gas for maintaining the gas between the anode and cathode in ionized condition due solely to collision be tween the particles and gas molecules whereby only a small potential difference is needed across the cathode and anode of the tube for defining the value of the discharge current through the thus initiated and maintained plasma.

2. A gas filled discharge tube as in claim 1, wherein the said particle emitter is a beta-particle emitter material.

3. A gas-filled discharge tube in accordance with claim 2 in which the anode, cathode, control electrode and particle emitter are mounted within the envelope and including shielding means between the particle emitter and the ionizable gas which isimpervious to the ions but pervious to the emitted beta particles.

4. A tube according to claim 3 in which the said shield comprises a cylinder supporting on the outer face thereof the electron emitting layer of the cathode of the tube.

5. A gas-filled discharge tube in accordance with claim 3 including a plurality of thin rods in close proximity to the electron-emissive layer, said rods supporting the particle emitting layer and the shielding means.

6. A .tubeaccording to claim .2, wherein the said beta ray emitting material is selected from a group comprising Silicium 31-, Carbon 14 and Thallium 204.

7. A .tube according to claim 1 and wherein the cathode of, the tube is of the cold cathode type.

8. A tube according to claim 1 wherein the cathode of the tube is of the thermionic kind.

9. A tube according to claim 3 wherein the electrodes the cylindrical and in nested relation, the anode being the external electrode and the beta ray emitting material consists of a film over the inner face of the cylindrical metallic tube supporting the electron emitting layer of the cathode.

10. A tube according to claim 3, wherein the said shield is of thin nickel.

11. A. tube according to claim 1 wherein a positive biasing battery is connected across the anode and cathode thereof and a negative bias battery is connected across the cathode and control grid thereof, a series input signal receiving impedance in the said cathode to control grid connection and a series output signal collecting impedance in the cathode to anode connection thereof.

12. A tube according to claim 1 wherein the gas is selected from a group consisting of neon, helium, nitrogen, hydrogen, argon, xenon, krypton, quicksilver and cadmium vapors.

13. A tube according to claim 3 wherein the beta ray shield is between the said beta ray emitter and the envelope of the tube.

14. A tubeaccording to claim 8 wherein part at least of the beta ray emitting material is deposited over the heater filament of the thermionic cathode of the tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,145,735 Ainsworth July 6, 1915 1,748,385 Loewe Feb. 25, 1.930 2,552,050 Linder May 8, 1951 2,616,986 Coleman Nov. 4, 1952 2,647,067 Williams July 28, 1953 2,672,567 Alvarez May 16, 1954 2,754,428 Franks et al. July 10, 1956 2,789,240 Cohen Apr. 16, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,892,967 J ne 30, 959

Jacques Marie Noel Hanlet It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 25, for "from the the" read from the column 4, line 40, for "the cylindrical" read are cylindrical Signed and sealed this 5th day of April 1960.

(SEAL) Attest:

ROBERT C. WATSON Commissioner of Patents KARL H, MINE Attesting Ofi'icer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,892,967 Jun 30, 1959 Jacques Marie Noel Hanlet It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 25, for "from the the" read from the column 4, line 40, for "the cylindrical" read are cylindrical Signed and sealed this 5th day of April 1960.

(SEAL) Attesti KARL H, AXLINE ROBERT C. WATSON Attesting Officer I Commissioner of Patents

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