US2552050A - Method of and means for generating electrical energy - Google Patents

Description

y 1951 E. G. LINDER 2,552,050

METHOD OF AND MEANS FOR GENERATING ELECTRICAL ENERGY Filed June 25, 1946 2 Sheets-Sheet} INVENTOR. Lin

y 1951 E. .G. LINDER 2,552,050

METHOD OF AND MEANS FOR GENERATING ELECTRICAL ENERGY Filed June 25, 1946 2 Sheets-Sheet 2 INSULATION LOAD Z #vsumnom IN VEN TOR. Ernes26l1nder ATTORNEY Patented May 8, 1951 METHOD OF AND MEANS FOR GENERATING ELECTRICAL ENERGY Ernest G. Linder, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 25, 1946, Serial No. 679,085

8 Claims.

This invention relates generally to the generation of electrical energy and more particularly to unique methods of and means for deriving and utilizin the electrical energy of nuclear reactions.

The enormous magnitudes of energy provided by certain nuclear reactions of some radioactive substances provide a tremendous field for the development of new sources of electrical energy. Since radioactive radiations (energy) are largely electrical in nature, it is desirable that such electrical energy be converted directlyto electrical energy of usable form. The alpha-particle and beta-particle emissions from certain radioactive substances comprise positively or negatively charged particle rays, respectively, having energies which vary from low values to several million electron volts. Other charged and uncharged particles also may be emitted. For example, alpha-ray emission comprises positively charged particles having energies varying from zero to the order of ten million electron: volts, while beta-particle emission comprises negatively charged particles having energies varying from low values to the order of three million electron volts. Nuclear reactions are known to provide either alpha-particle emission, beta-particle emission, or a combination of alpha-particle and beta-particle-emission, as. well as other types of charged and unchargedparticles not generally so well known. The direct utilization of the high electrical potentials which may be derived from such charged particles provides, in the cases in which the particle emission is charged, much more convenient and efiicient utilization of nuclear energy than previously proposed systems wherein the nuclear energy is converted to thermal energy, the thermal converted to mechanical energy, and the mechanical energy then converted to electrical energy in a usable form. Also, the direct utilization of the electrical energy of nuclear reactions may be much more readily controlled by electrical methods than may the conversion of nuclear energy to thermal energy.

The instant invention is an improvement over the methods and systems described and claimed in applicants copending U. S. application, Serial No. 679,081, filed June 25, 1946, now Patent No. 2,517,120, August 1, 1950, which contemplates the use of collector electrodes for collecting the charged particle rays from a radioactive source, and means for applying the resultant unidirectional potential between the source and collector electrodes to a load; The improvement comprising the instant invention includes unique inethods of and means for segregating and utilizing separately the electrical properties of alphaparticle and beta-particle or other charged particle emission from radioactive materials to generate separate voltages and thence combining said voltages. It utilizes the distinguishing characteristics of differences in charge, polarity, mass, velocity and penetration of diiierent types of such particles.

Among the objects of the invention are to provide improved methods of and means for gen-- erating electrical energy in response to nuclear reactions. Another object is to provide improved methods or" and means for utilizing the electrical energy in nuclear reactions for generating high unidirectional potentials. A further object is to provide improved methods of and means for utili'zing the electrical energy of nuclear reactions for generating alternating potentials. An additional object is to provide improved methods of and means for utilizing atomic energy for generating electrical energy. A still further object of the invention is to provide improved methods of and means for utilizing radioactive materials as sources of electrical energy.

Another object of the invention is to provide improved methods of and means for converting atomic energy directly to electrical energy in commercially usable forms. A still further object is to provide improved methods of and means for segregating and separately utilizing the electrical energy of alpha-ray and beta-ray or other charged particle emissions of radioactive materials for generating electrical energy.

Other objects of the invention include improved methods of and means for converting the electrical energy of nuclear reactions of radioactive materials to high frequency electrical energy. A still further object is to provide improved methods of and means for utilizing and combinin the alpha-ray and beta-ray electrical potentials of nuclear reactions for directly deriving electrical energy in commercially usable form;

The various embodiments and features of the invention will be described in detail hereinafter by reference to the accompanying drawings of which Figure 1 is a schematic disgram of a basic embodiment of the invention according to said copending application and including a simple unidirectionall voltage generator; Figure 2 is a cross-sectional diagram of a modification of said basic embodiment of the invention; Figure 3' is a cross-sectional schematic diagram of another modification of said basic embodiment of the invention; and Figures 4 and 5 are cross-sectional,

. source terminal 9.

partially-schematic diagrams of first and second embodiments of the instant invention each utilizing combinations of alpha-ray and beta-ray emission for generating electrical energy. Similar reference characters are applied to similar elements throughout the drawings.

High-ololtage D.-C. generators Referring to the drawings, Figure 1 illustrates the simplest form of the basic embodiment of the invention disclosed and claimed in said copending application comprising a unidirectional high voltage generator I. The generator I includes a source 3 of alpha-rays or beta-rays derived from a quantity of radioactive material. A suitable alpha-ray radioactive source may comprise, for example, a quantity of polonium (84Po Likewise, a suitable beta-ray source may comprise a suitable quantity of radioactive phosphorus (15P Radioactive phosphorus is a pure beta-ray emitter which becomes stable after emission. It is thus suitable for use as an electronic power source since it emits no gaseous reaction products and, therefore, it is suitable for vacuum applications. One gram of this material occupies about .5 cubic centimeter and will emit about 2 milliamperes of electron current. The maximum energy of the beta rays is of the order of 1.7 million electron volts, but only a small fraction of the electron current would be available at such a high voltage. However, about 1 milliampere of current would be emitted at one megavolt. Since the average energy of emission would be about 1 million electron volts, the total electrical energ or power emitted would be about 2 kilowatts. The half-life period of radioactive phosphorus (151 is about 14 days, and the current and power would decrease exponentially to one-half their initial values in that time.

The radioactive source 3 is surrounded, for example, by a spherical highly evacuated conductive collector electrode 5 having an aperture insulator l therein for a suitably insulated terminal 9 for the radioactive source 3. A load II is connected between the collector electrode 5 and the If desired, the collector electrode 5 may be grounded.

In operation, and in the absence of a load, beta particles (electrons) emitted by the radioactive source 3 travel to the collector electrode 5 and charge it negatively as indicated by the dash line arrow I3. The charge upon the collector electrode is negative with respect to the source 3 and increases until the potential of the collector electrode is sufficiently high to repel additional electrons arriving from the source 3 is shown by the dash line arrow l5. If it is assumed that the radioactive source 3 emits 1 megavolt electrons (beta rays), the potential of the collector electrode 5 would reach one megavolt and would be negative with respect to the radioactive source. If a load is connected between the collector electrode and the source terminal, a current will flow through the load and power will :be dissipated therein. Thus the radioactive energy emitted in the beta rays may be employed directly in its original electrical form to provide electrical energy.

Known beta-ray emitters provide electrons having energies from almost zero to 3 million electron volts. Known alpha-ra emitters provide positively charged alpha particles having energies from about zero to the order of 10 million electron volts. If desired an alpha-particle sourc may be employed instead of a beta particle source, in which case the collector electrode 5 will be charged positively until it reaches a potential sufficiently high to repel additional alpha particles. In such a modification Of the invention, the collector electrode 5 becomes the positive terminal and the radioactive source 3 the negative terminal of the generator. Obviously other types of charged particles may be utilized.

The electric current produced by any source of charged particles is 1,edt (1) where n is the number of particles emitted, t is the time in seconds, and therefore dn/dt is the rate of particle emission, and e is the electrical charge per particle. If each particle carries more than one electronc charge, 6 must be replaced by e, where ,u. is the number of charges.

For a radioactive substance (see Pollard and Davidson, Applied Nuclear Physics, p. where is the decay constant The number of atoms contained in a substance of mass M and atomic weight A is where m is the mass of the hydrogen atom. Thus O.693 M611. m At (6) This relation may be expressed in amperes per gram for a predetermined quantity of a radioactive substance wherein c=1.59 x 10- coulombs, M 1 gram, m =1.66 10 grams, and t 8.64 10 T where T is the half life in days. Therefore,

If the radioactive source is polonium, A=2l0 and T =140, :2, therefore 5 1 .8 microamps. gram The characteristics of the charged particle emitting substance determine not only the output voltage of the generator, but also determine its impedance. Thus, since alpha particles generally have a very uniform energy, the generated voltage would remain substantially constant until all the remaining current was drawn, whereupon the Voltage would decrease rapidly. Thus, with an alpha-particle emitter, the generator would have a low effective internal impedance. In contradistinction thereto, beta particles are usually emitted over a wide energy range which may vary from a very low value to several million electron volts. Consequently, when current is drawn from the generator to a load, the load voltage would immediately drop to a much lower value than the no load maximum, as is characteristic of all generators having high internal impedance. The actual variation of load voltage with current would depend upon the particular characteristics of the beta-ray emitting material. In general the available power depends upon the quantity of radioactive material employed and upon its rate of particle emission. Materials. which emit at high rates have short operating life, while materials emitting at low rates have relatively longer operating lives. A D.C. generator of the type described has particular application for systems requiring high voltage and low power capacity sinc in such instances only a relatively small amount of radioactive material is required for the alphaor beta-ray source.

For generators providing relatively large power values, cooling of the charged particle source may be necessary or desirable since the source is bombarded and heated by the returning charged particles which are reflected by the charged collector electrode. Also the collector electrode is heated by the charged particles which it'collects. A simple system for cooling the charged particle emitter is shown in said copending application wherein the charged particle source 3 comprises a relatively thin shell of radioactive material into which air or water under pressure may be forced for cooling purposes. If desired, the collector electrode may be cooled by air blasts.

Secondary electron suppression The principal limitations onthe potentials which may be attained by the device described heretofore is dueto leakage currents. Some of the leakage currents are due to the inherent limitations of insulating materials and the proportions thereof as determined by the proportions of the generator unit. Insulator leakage currents may be reducedto negligible values by employing insulator materials and shapes commonly used in high voltage work. Another serious source of leakage currents arises from the nature of radioactive radiations themselves.

Referring again to Figure l of the drawings, beta rays striking the collector electrode 5 will cause secondary electron emission therefrom.

Such secondary electrons will be attracted toward the radioactive source 3 which is positively charged with respect to the collector electrode 5, and thus will tend to neutralize the positive charge on the radioactive source and hence decrease the potential difierence between the source 3 and the collector 5-. a

Referring to Figure 2, inorder to reduce the efiect of secondary electron emission from the collector electrode 5, a grid or thin metallic shell H is introduced into the generator in a region intermediate the source 3- and collector 5, and is maintained at a comparatively small negative potential with respect to the collector electrode 5 by a battery it. connected between. the. collector and grid electrodes. The biasing potential may be of the order of 100 to 1000 volts. As explained heretofore, this potential may be derived from a separate radioactive D.-C. generator since the energy required is practically negligible. The negatively biasing grid electrode i'i suppresses substantially all secondary electrons emitted by the collector electrode 5 and thus permits the potentialsbetween the radioactive source 3 and 'the collector electrode 5 to build up to a value determined by the velocity of emission of thebeta raysand the load resistance, as described heretofore.

Alpha-particle; suppression.

A further source of'leakage wouldoccur in instances wherein the radioactive source- 3" emits Delta-particle suppression Referring to Figure 3, when an alpha-particle radioactive source is employed, leakage may result due to 6 rays which are slow electrons which accompany the emission of alpha rays. Such 6 rays would be drawn to the collector electrode 5, which in this instance would be positively charged with respect to the alpha emitting source 3, and would result in charge neutralization on. the collector electrode. To decrease this effect, the alpha particle emitting source 3 may be surrounded by a grid 23 which is maintained at. a comparatively low negative voltage with respect to the alpha-particle source 3. This voltage may be derived from an external battery 25 connected between the source 3 and the grid 23 or it may be derived from an auxiliary radioactive generator. The bias voltage applied to the grid 23 should be sufficiently high to suppress and reflect back to the source substantially all 6 rays emitted by the radioactive source 3, but will have little. efiect upon the highly positively charged alpha particles emitted by the source.

Controllable radioactive generators When employing. radioactive materials (either natural or artificial) for the production of electricah energy, the radioactive emission will decay exponentially as a function of the type of radioactive material employed. The decay of radioactive: emission will provide a corresponding decrease in the; energy. which may be derived from the. generator. This. decay is uncontrollable since the active material is consumed. Whether or notpcwer. is derived from the generator.

By utilizing. a reaction or. series of reactions of the. proper types, it is. possible to providev a radioactive electric generator which will. consume. the. radioactive material and deliver electrical energy only when desired. An example of suchareaction is asfollows:

' in any other manner and with any other structure'known' in the art;

' Following-is-a partial'list" of'alphaandbeta-r 7 ray emitters which are suitable for high voltage generators of the types described heretofore:

Energly, t Half-life i 911 Element million 9 days electron volts ALPHA-RAY EMITTERS l 25 10 Polonium (P0 4 Actinium (Ac 11. 2 5. 66 Thorium X (Th X 3. 64 5. 65 Radio actinium (Rd A0 18. 9 5. 92

BETA-RAY EMITTE RS Phosphorus (P 14 1.7 Calcium (Ca 180 Scandium (S0 S5 26 Iron (Fe 47 Arsenic (As 16 1.1: Strontium (SI 55 l. .1 Antimony (Sb l. 69 l. 53 Tungsten (W 74 (l. 5

Combined alphaand beta-ray generators High voltage D.-C. generators may be provided to utilize a radioactive emitter providing both positive and negative charged particles (alpha and beta rays or other charged particles of both polarities and differing velocities and penetration). An emitter of both alpha and beta particles is radium (C). A mixture of substances such as radioactive polonium and radioactive phosphorus also may be utilized. The polonium provides pure alpha ray emission, and the radioactive phosphorus provides pure beta-ray emission. Such mixtures are frequently preferable since the ratio of the number of alpha and beta particles may be controlled.

Referring to Figure 4, a radioactive source 21 providing both alpha and beta particle emission is supported by terminal 29 from a high voltage insulator which also supports a spherical evacuated beta-ray collector electrode 33. A thin metallic alpha-ray collector electrode 35 is interposed between the source 2'? and the betaray collector electrode 33. The alpha-ray collector electrode should be of sufficiently thin material to be substantially opaque to alpha rays while substantially transparent to beta rays, as explained heretofore by reference to the device illustrated in Figure 2. A terminal 31 supports the alpha-ray collector electrode 35 and is insulated by a second high voltage insulator 39 from the beta-ray collector electrode 33.

In operation the alpha-ray collector electrode 35 becomes positively charged to the potential of the alpha rays, and the beta-ray collector electrode 33 becomes negatively charged to the potential of the beta rays, both with respect to the source 21. The voltage which may be applied to a load 4| thus is the sum of the magnitudes of the voltages established on the electrodes 33 and 35.

It is essential for proper operation of the device that the rate of arrival of alpha particles on the alpha-ray collector electrode 35 exceed the rate of arrival of beta particles by direct capture and by reflection from the beta-ray collector electrode .0 33. Suitable proportions of alpha ray and beta ray radiation may be assured by providing a suitable mixture of alpha-ray and beta-ray emissive substances in the radioactive source 21.

- Amore complex structure utilizing combined alpha-ray and beta-ray emission for generating high D.-C. voltages is shown in Figure 5 wherein a combined alpha ray and beta ray emissive source 43 is in the form of a hollow shell which is insulated from and surrounded by an evacuated spherical beta-ray collector electrode 45. A secondary electron suppressor grid or thin shell 41 is interposed between the beta-ray collector electrode 45 and the radioactive source 43 to prevent secondary electron emission from the beta-ray collector electrode from reaching and neutralizing the potential of the radioactive source 43. An alpha ray suppressor electrode 49 comprising a thin sheet of aluminum or other suitable material opaque to alpha-ray emission but substantially transparent to beta-ray emission surrounds the external surface of the radioactive source 43. Thus the voltage on the beta-ray collector electrode 45 with respect to the radioactive source 43 is substantially dependent only upon beta-ray emission.

An alpha-ray collector electrode 5| is disposed at the center of the hollow radioactive emitter 43 and is insulated therefrom in any suitable manner. A beta-ray suppressor grid 53, biased negatively with respect to the radioactive source 43, is disposed between the alpha-ray collector electrode 5i and the radioactive source 43. The negative potential for the beta-ray suppressor grid may be derived by means of a direct connection between said grid and the beta-ray collector electrode 45 whereby said grid is self-biased by the beta-ra emission.

The voltage established upon the alpha-ray collector electrode 51 thus is dependent substantially only upon the alpha-ray emission from the radioactive source 43. The sum of the voltages developed upon the beta-ray collector electrode 45 and the alpha-ray collector electrode 5| may be applied directly to a load 55.

One of the advantages of the more complex structure illustrated in Figure 5 over the simple combination alpha and beta ray generator of Figure 4 is that undesirable reaction upon the alpha ray collector electrode due to reflected or secondarily emitted electrons from the beta-ray collector electrode is substantially eliminated, thus reducing leakage currents. 'It should be understood that the relative positions of the alpha-ray generator portion and the beta-ray generator portion of the device may be interchanged with respect to the radioactive source. The principles and techniquesof the instant invention also may be applied to the'generation of alternating potentials including energy of microwave frequency by proportioning the collector electrodes to resonate at the desired output frequency a disclosed and claimed in applicants copending U. S. application, Serial No. 679,083, filed June 25, 1946.

Thus the invention described and claimed hereing comprises unique methods of and means for generating unidirectional or alternating potentials by utilizing directly the electrical properties of radioactive emission. Such generators may provide high or low unidirectional potentials with relatively low or relatively high current output, respectively; and alternating potentials including A.-C. energy of microwave frequency. Control and focusing potentials for said devices may be provided by auxiliary radioactive generators, or self-biasing arrangements may be employed. Combinations of both alphaor beta-ray emission may be segregated or utilized separately.

I claim as my invention:

1. The method of utilizing a source of radioactive material providing positively-chargedparticle and negatively-charged-particle emission for generating electrical energy comprising segregating and collecting said positivelycharged-particle emission in a first region adjacent to said source to establish a first potential with respect to said source, collecting said negatively-charged-particle emission in a second region adjacent to said source to establish a second potential with respect to said source, substantially preventing charged particle interaction between said regions, and combining said potentials.

2. Apparatus for generating electrical energy including a source of radioactive material providing both alpha-particle and beta-particle emission, means disposed adjacently to and in cperative relation with said source for collecting said alpha-particle emission to establish a positive potential with respect to said source, second means disposed adjacently to and in operative relation with said source for collecting said betaparticle emission to establish a negative potential with respect to said source, means for substantially preventing alpha-particle irradiation of said second means, and means for combining said potentials.

3. Apparatus for generating electrical energy including a source of radioactive material providing both alpha-particle and beta-particle emission, first means substantially transparent to beta-particle emission and substantially opaque to alpha-particle emission surrounding said source for collecting said alpha-particle emission to establish a positive potential with respect to said source, second means surrounding said source and said first means for collecting said beta-particle emission transmitted through said first means to establish a negative potential with respect to said source, and means for combining said potentials.

4. Apparatus for generating electrical energy including a source of radioactive material providing both alpha-particle and beta-particle emission, first means substantially transparent to beta-particle emission and substantially opaque to alpha-particle emission surrounding said source, second means surrounding said source for collecting said beta-particle emission transmitted through said first means to establish a negative potential with respect to said source, third means in operative relation with said source for collecting substantially only said alpha-particle emission to establish a positive potential with respect to said source, and means for combining said potentials.

5. Apparatus for generating electrical energy including a hollow body source of radioactive material providing both alpha-particle and betaparticle emission, first screen electrode means substantially transparent to beta-particle emission and substantially opaque to alpha-particle emission surrounding said source, second means surrounding said source and said first means for collecting said beta-particle emission to establish a negative potential with respect to said source, a secondary-electron-suppressor electrode disposed between said first and second means for preventing secondary-electron emission from said second means from reaching said source, third means disposed Within said hollow source for collecting substantially only alpha-particle emission to establish a positive potential with respect to said source, a beta-particle suppressor electrode disposed between said third means and said source for substantially preventing betaparticles from reaching said third means, and connections to said second and third means for combining said potentials.

6. The method of utilizing a source of radioactive material providing pos'itively-charged-particle and negatively-charged-particle emission for generating electrical energy comprising segregating said charged particles as a function of their penetrating characteristics in a retarding medium, collecting said positively-charged-particle emission in a first region adjacent to said source to establish a first potential with respect to said source, collecting said negatively-chargedparticle emission in a second region adjacent to said source to establish a second potential with respect to said source, and combining said potentials.

7. The method of utilizing a source of radioactive material providing positively-charged-particle and negatively-charged-particle emission for generating electrical energy comprising segregating said positively-charge-particles as a function of their penetrating characteristics in a retarding medium, collecting said positivelycharged-particle emission in a first region adjacent to said source to establish a first potential with respect to said source, segregating said negatively-charged-particles as a function of their penetrating characteristics in said retarding medium, collecting said negatively-charged-particle emission in a second region adjacent to said source to establish a second potential with respect to said source, and combining said potentials.

8. The method of utilizing a source of radioactive material providing positively-charged-particle and negatively-charged-particle emission for generating electrical energy comprising segregating said charged particles as a function of their penetrating characteristics in a retarding medium, collecting said positively-charged-particle emission in a first region adjacent to said source to establish a first potential with respect to said source, collecting said negatively-charged-particle emission in a second region adjacent to said source to establish a second potential with respect to said source, and utilizing said potentials.

ERNEST G. LINDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,964,738 McCreary July 3, 1934 2,032,545 McElrath Mar. 3, 1936 OTHER REFERENCES Physical Review, vol. 69, June 15, 1946, page 666 (A. E. D),

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