US2669609A - Electron discharge device - Google Patents

Description

Feb. 16, 1954 E. G. LINDER 2,669,609

ELECTRON DISCHARGE DEVICE F'iled Oct. 50, 1948 I firing? filljnder f A. m

ATTORNEY 'ztented Feb. 16, 1954 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE Ernest G. Linder, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 30, 1948, Serial N 0. 57,428

8 Claims.

This invention relates to electron discharge devices and particularly to such devices in which the medium in which the discharge takes place is a liquid, or a gas near or above atmospheric pressure, or a solid or mixtures or combinations thereof.

The mean free path of an electron in a gaseous medium decreases with lower electron velocities, down to certain values, and increases with lower pressures of the medium. When ionization has been desired heretofore in the conventional electron discharge devices, an accelerating voltage in the form of an electric source had to be made available and applied electrostatically to the electrons in the medium to bring their velocities up to and exceeding ionizing values and the accelerating voltages have had to be of such values that the velocities of the electrons were brought up to the ionizing velocities of the electrons before collisions occurred with molecules of the medium. Because of the lengths of the mean free paths of electrons in gas media of conventional pressures and the accelerating voltages normally available, high vacuum gas media have had to be used.

It is known that certain isotopes are radioactive and emit primary nuclear charged particles at known rates over known periods of time and over a range of energy values or levels expressed. in electron volts. Some emissions consist of positively charged or alpha particles, others of negatively charged or beta particles, and others of both alpha and beta particles.

The unique properties of radioactive materials are not affected by temperature or pressure conditions or the physical characteristics of the media into which the particles are radiated. What reactions take place between the primary particles and the molecules of the medium after the particles have left the radioactive source does depend upon the physical characteristics of the medium. The magnetic and electric fields present in the medium affect the directions of movement and velocities of the charged particles.

For example, a beta particle emitted at l Mev. normally produces about 10 ion pairs. If such radiation takes place in air at atmospheric pressure and the total ionization effect of the radiation is desired to be utilized in an electron discharge device, the envelope of the device would have to have a radius of several meters as the range of a l Mev. beta particle in air is about that distance. If, however, the air is confined under pressure, air-medium electron discharge devices of practical dimensions may be utilized,

as the mean free path of an electron in that medium is much shorter than that in air at atmospheric pressure.

Likewise, shorter mean free paths and hence shorter ranges may be availed of by selecting some liquid that is normally an insulator, for example an oil, or even a solid, such as a low density hydrocarbon with or without other elements in chemical solution or suspension, or mixtures of liquids, gases or such solids, as the medium to be ionized. Thus a "dense medium is provided in the electron discharge device of this invention.

With high energy primary charged particles available from a radioactive source as the ionization initiating particles, the emission of secondary electrons per collision will be high, as willcient energy is available not only to knock out electrons from the outer shells of the molecules but also some electrons from the inner shells will be projected into space.

In this specification and appended claims, a "dense medium is defined as a medium in which the molecules are spaced relatively close together and includes a liquid Or a solid or a gas at or near atmospheric pressure or substantially above atmospheric pressure. Also, a medium is defined as ionizable when it has the characteristics of the general class of materials known as insulators and the electrons in the outer shells of the atoms making up the molecules are not so tightly bound to the nuclei of the atoms that they can not be knocked out of their orbits by emitted nuclear particles or moving free electrons.

In selecting a radioactive isotope from the large number of choices, consideration may be given to the energy of the primary particles emitted, the half life of the isotopes, the character of the element to which the atoms of the isotope decay, and the general availability and cost of the isotope. Phosphorus and strontium are examples of suitable radioactive materials as they are beta emitters with a spread of velocities up to l Mev. It will be understood, however, that other suitable emitters are well known in the art, as published in the literature.

In selecting a solid or a liquid or a gas to be used as the medium, consideration may be given to the general availability and cost of the material and, in the case of gas, the pressure to be used to obtain the desired molecular mean free path. The molecular mean free paths in various gases are generally known in the literature.

For isotopes having high energy values and sociated circuits beingdgenerallyapplicable-to the -present-rinvention. I

gases having relatively long molecular mean free paths, a magnetic field may be impressed upon the medium and a collecting electrode may be placed in the device near one end of the anode. When this electrode is connected to an electric source, the primary particles and the secondary emission electrons are caused to be drawn into cyclic paths and tliusz the paths of thes'e pa'rticles and electrons are lengthened to and beyond the value of the mean free path of the particles for ionization by collision. It is not stood that only the high velocity-primary partir cles cause the initiating of secondary electrons; The lower velocity primary) to be under particles likewise "'i'gr'am' of thedevice shown in Figural incorporated collide with the molecules:of' theimedium sand 5 cause ionization.

While the velocities of the projected secondary electrons are very much less 'than'those of'the" high energy primary particles, these-secondary! the elec trio fields -have suflicient-'energy to-move through the mediumandacause Y further ionization of the electrons, with gains in: velocities from medium by collision withathe:moleculesof? the JI'his invention is -relatedto the invention- -d'isclosed in; copending application Serial No. 51,756 1 filed September 29,1948, in which applicationsis disclosed and; claimed a high vacuum electron discharge device and associated circuitaltheas- Among the vobjects ofith e invention .are .Ithe

o providing or: improved methods'of and ineans'ifor -obtaining large electronudis'charge currents.

Another. object-islto provideaanlimproved electron idischarge device vin which lthe discharged medium is a liquid, La solid,- or agasatpresSures approximately .at or "substantially above, atmospheric pressure, or in desired combination or Jin Figure 2 incorporated v.lcuit; and Figure 6 is into a detector? circuit? Figure ads atschematic diagram of a modification of the device shown into an amplifier cira schematic diagram of another modification of the device shown in Figure incor-poratedl-into an amplifier circuit.

"ifcorresponding numerals throughout the drawings refer' to'Fcorresponding parts.

.Referring to Figure l, numeral 1 is a radioactiveisotope"ch"rged particle emission source material: deposited on a rod 2 that is positioned in the axis of electrode or anode 3, which is cylindrical-in-.form; Rodi and anode 3" are mounted-by any-conventionalLmeans in an en- 1 velope lw The envelopeiisfilled'with a normally etinsu lating or noneconductive liquid .5 or solid l 5 near.-one endof anode in the envelope-4, which filled with some gaseous medium, shown; generally ate. .Th'e'ienvelope] is made of some "ma- .terial, suchlas I new, produced..lby..solenoid 9 "when connected. to a=-source connection of direct current l 0; is im- Qpressed axially ,andsource l. .Ne'arthe en'd'of anode 3;"opposite tothe end near which the source"! is positioned, 40

orm. o l

Another object isto'piov-ideah improved electron discharge device inf which the initiating ionizing 'source'of poweris ara'dioactivematerial or isotope. V

Another object'is to provide an improved elecnected to the 'ra'dioactive'sou'rce I that is ionizablehy.collision-by. the charged'primary particles from source l. Connectionsto rod 2. and-anode. 3oareprovidedmith conductor wires-:6 andf. respectively. a

' Referring to. Figure 2,..the radioactive isotope source material |-is-.posinonea.in the .axis' ofand glass, .such that I the magnetic upon the space between'anode. 3

is mounted. a collecting'electrode" l I." This electrode' lf'is connected lto 'thepositivepoleof a source of electric?potentialilz "b'ybwirel'3; the negative" terminal of said source I2 being conahdanintermediate point of 'potenti'alibeing connected to theanode'i and." grounded;

' The magnetic i':field"is not required to 'be used in'iall cases where the ionized medium is agas.

" The molecillar an'delectronmean' free paths of tronidischarge .deViCein WhiCh thednitiating I ionizing source of. poweri'is' a'radioactiveisotope r 'andin which thesecon'daryj electrons projected from the molecules of the ionized medium by the radioactive radiation have andlgainlfrom'the electric fields sufiicient energyto'causeiurther ionization of the medium and' th'ereby effect cum'ulative' ionization.

Another object is toi-provide an improvedelectrondischarge device in which the lengths of the. paths. of "the .electronsinitiated by collision wanna; molecules of themediumare' lengthened"beyond the mean free pathfor ionization -by v collision i to effect further ionization cfthe medium.

"Another object is tojprovide an improvedelec- "tron discharge device adaptable for use as'a rectifier "or a' detector.

Another object is to provide an improved elec- "tron disc'harge device adaptable' ror" use as an 11 amplifier;

1 Other? objects will be tapparent fromthe dis closure vofthe invention as hereinafter setwforth in detail and from the.-- drawings ==made a part hereof in whichz-Figure l-is aischematic diagram of a discharge a device of the invention) .in r-which I the rmeclium is-aliquid or -a.-solid or-la gasnnder electrons along 'the axis-of the Q} J some gases are so relatively short,' and especially at pressures substantially above atmospheric pressure; forfexample, '2"atmos'pheres;' that "devices of "practical "dimensions may "be used without the need of extendingthepa'ths ofthe particles and device;

; By thetadjustment of the positive potential on '1: collector" l l and by adjusting the strength of the catedh'y arrow"! lithe particles j emittedtby the radioactive "*source- 1 ami-the sec- ""ondary electrons aredefie'cted "from their normal pathsyl 5; into-"paths pne-whicltis represented-by the spiral 16. Thus the p'aths oi the' p'articles are lengthened'beyond the-*mean free pa'th'for ionization bycollision withthe molecul'e's of the gaseous medium 8 Because offthe dissymmetryof the electrodes,'the conduction-is non-linear and the A practical-*use of "the device' in-"a rectifier circuit is 'shown in"'"Figure Referring -to Figure 3,

the radioactive material xl 701 other .terminal of :the" secondary-being connected torcollector electrode -I isiiconnectedl-to itheione terminalpfi the secondary-f transformer I] the i through load-l 8 and electr-icsource l2. Electrode- H is connected toh the positive terminal of. source .l2. Anodei3 is kept positive "with respect -to sourcel by electrical source I9, which is connected between anode 3 and source I, the positive terminal of source I9 being connected to anode 3. The primary of transformer I1 is connected to the alternating current to be rectified.

In operation: The primary charged particles are emitted from source I in random directions. Under the force of the magnetic field set up by the solenoid 9 and the electric field set up by electric source I2, the particles strike the anode 3 at varying angles of incidence according to their random directions of emission and the effect of the magnetic field I4, and cause secondary emission of electrons. Also, as the paths of the individual primary particles are lengthened by their assuming the form of a spiral under the effect of the magnetic field I4 and the electric field set up by source l2, their lengths become such that ionization occurs by which further secondary electrons are projected from the molecules of the medium. These secondary electrons collide with other molecules of the medium and produce further or cumulative ionization. The mean free path between molecules of the gaseous medium may be selected b choosing certain gases as the medium, the molecular mean free paths of which are generally known. Also, the molecular mean free path of a gas may be shortened by increasing the pressure of the medium.

Electric source I2 is adjusted such that electrode II is positive only during one half of the cycle of voltage variations between the two ter minals of the secondary of transformer It. When electrode II is positive with respect to source I, the device is conducting and through load I8. When electrode I I is negative with respect to source I, the device is non-conducting. Electrical source I9 maintains anode 3 positive with respect to source I. The varying current to be rectified is supplied to the primary of transformer I1.

The useful load to which the circuit is to be applied, is connected as shown as at I8. A resistance may be substituted for this load and the drop of potential along this resistance becomes available for use in circuits outside the circuit disclosed.

Figure 4 shows a detector circuit similar to that in Figure 3, but using the device shown in Figure 1 as a substitute for the device shown in Figure 2. A magnetic field and a collecting electrode are not required as the electron mean free path for ionization by collision of a solid or liquid are very short compared with those in a gaseous medium.

In Figure 4, the rod 2 supporting source I is connected to anode 3 through the secondary of transformer I'I, load I 8, and electric source I 2. The source of the current to be rectified is connected to the primary of the transformer II. The initial ionization by the primary particles, the resulting secondary emission of electrons and the further ionization by collision of the initial secondary electrons with molecules of the medium, take place as previously described.

Figures 5 and 6 illustrate the practical uses of the device in amplifier circuits.

Referring to Figure 5, the modulated currents to be amplified are supplied from their source 20 to a section H of the solenoid 9 of Figure 2. For very small currents, section 2| may constitute all of solenoid 9 of Figure 2. The magnetic field, shown as arrow I I, is created by the currents through coil 2| and solenoid 9. The strength of the magnetic field, therefore, follows the char acteristics of the current source 20. Source I and electrode 3 are connected to the collector eleccurrent will fiow' trode II through load I8 and biasing electric source I9. Biasing electric source I9 is connected between anode 3 and source I, the positive terminal of electric source I9 being connected to anode 3.

In operation: As the magnetic field is created by the currents from source 20, variations in such currents change the forms of the spirals I6 and therefore the extent of ionization of the medium 8 and hence cause changes in the currents through load I8, which correspond with the variations in the currents from source 20.

Another amplifier circuit is shown in Figure 6 in which the radioactive material I is deposited on rod 2 and extends for some distance along the axis of anode 3. The source of the currents to be amplified is connected to the primary of transformer I'I. One terminal of the secondary of the transformer I1 is connected to electrode 3 through biasing electric source I9. The other terminal of the secondary of transformer I8 is connected to rod 2 and to collector electrode II through load I8 and electric source I2. The current through solenoid 9, to create the magnetic field 8, is supplied from a direct current source connection I I).

In operation: The variations of the currents in source 20 create through transformer I1 amodulating potential on electrode 3 and also impresses on source I and electrode II potentials opposite in sign. The effect of these changing potentials is to change the electric field between the electrode II and anode 3 and source I and hence cause variations in the ionization of both initial secondary electrons ejected from the orbits of the atoms of the gas as well as ionization by collisions of the initial secondary electrons with the atoms of the gas. The collections of electrons by electrode II is therefore, changed in accordance with the variations in the currents from source connection 20. The characteristics of the currents through load I8, therefore, correspond to those of source 20.

By extending the length of source I along the axis of anode 3, the control effect of the magnetic and electric fields is sharper as the number of primary particles are increased and a greater aiumber of electrons are produced in a shorter line.

This invention, therefore, makes use of the radiation of nuclear particles from radioactive isotopes to initiate secondary electrons by the ionization of a medium, not only by the collisions of the primary particles with molecules of the medium, but also by the further collisions of the projected secondary electrons with molecules of the medium. A cumulative ionization, with large attending currents, is thereby obtained. By controlling the generation of these currents by currents from an independent source, such as a signal, the device is useful as a detector or an amplifier.

I claim as my invention:

1. An electron discharge device comprising: a concentrated radioactive charged particle emission source, a cylindrical anode, the said source being positioned adjacent said anode, a collector electrode also positioned adjacent said anode and substantially separated from said source, an electric source connected to said collector electrode, an envelope surrounding said emission source, said collector and said anode, a dense ionizable gas confined within said envelope, connections for a source of direct current, connections for a source of varying currents, and a solenoid surmpotential' for said zano de electrode,aiantxenvelope surrounding'isaid emissionisource and: said: anode :electrode iamionizable- .medium" comprising smaten in i fwhi'ch-ithel'smolecules are; spaced relatively s l collectorsielectrodeiwithin said envelope positioned i adjacentzsaid:anodeiand .spacedfromssaid. source, wand connection means. for "aizsource of electric potential for saidecollector? ielectrodeyisaid medium arbeing' fadaptedzto beaionized. by .charged particle's emitted by said source to produc'e'za copiousfsupply'iof ionizatiomele'ctronsriorIcollection by said anode".and:collectorc-electrodes; 1

: BiBAn'electmrr zdischarg'e device-31 comprising: an

1 anode; a radioactive acharged .iparticleaemissiohsource posltioned-iadjacent said anode, t a collector electrode positionedradjacent. said anodeanda sub 'stantiallytseparatednqfroma said source; an electric source L -connected etc i: said-collectorelectrode; an

1:: envelope isurronndingisaid emission sou'rce, said ucollector. and esaidi anode; 'ansionizable "medium *icomprisingi matter in whi'ch: :xthe' molecules are 1 spaced relativelycc close vto'gethere confined within in said.=':envelope,.: terminals :for 'a sou-ree of direct it current;terminals: for ai; source "of varying our re'nts,'"= -and a2 solenoid. :surrounding and coaxial with saidanode, :a-portion' of: said solenoid being connected to said. idirectocurrent E iterrninalsw and another' -portion of said-solenoid being I connected :to:' said (varying current terminalsywhereby ihe changes in: theiimagnetic. -fieldl produced "by said olenoid: correspond.% in characteristics' to said :-.zvarying icurrents"and aivarying magneticfield is impressed on said medium along the axis of said .uja c l V: 4:1An'; electron:dischargevdevicertcomprising, a 5. ylindrical :anodeielectrode; connectionrmeansnfor :1; a source of .-ele,ctricz potential ion-said =anode elec- .--'an:= ;anode electrode positioned'adjacent :said ourcegiconnection meansio'r 1a source of electric 1 loseitogethen-confined :within;.,said? envelope, a 9- Liz-rode, agsupporttmemberdisposed'within saidan- 1 oderelectrodezaandqalong .itsaaxis' andthavinglead- 1; ;means, a "radioactiuezzchargedtparticle emitting material carried rby 1B,Jl1:3dl$tflblld alongnth 5 length of said support memhercapable ofyemitting 5-. schargedrparticlesqhaving energies oftheorder of onemillionelectron volts, a collector electrode p0- sitioned vadj acent saida: anode; electrode; lead-in lmeansiconnectedatos said collector. electrode,1:an wenvelope surrounding said; emission source,.= said anode; and said icoll'ector electrode; and an ionizable :medium comprising matter. in which the .7 molecules are; spaced relatively-close, together confined ".within' :saidys'envelope; said medium -Ibeing adapted-to -be:ionized-bygchargedi particles 1 emitted"; by saidv source 7 to produce a. copioussupply of =a ionizaticnrelectrons for collection by said-anode and collector electrodes. 1

5; :"An electron; discharge device a as claimed in i-claim Z'f-Wherein saidmedium is algae. a

62 An electron idlscharge "device as claimed in :claim 2iwhereinfsaidamedium is a kliquid.

' -An electron discharge-deviceas"claimed in claim :Z -Wherein said medium is a solid.

v 8: An :ele'ctroni discharge device: as A claimed in '-==1 claim' 2 whereinsaid medium is a mixture of materials.

ERNEST G.

References ,'Gited in the ;fileiof;..this; patent UNITED STATES PATENTS Mafia-1,144 m-Nov 21, 31950 umber l :iCountry. :".:Date

3325734 1%,; Great Britain ;L Aug. '7, 1930

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