By

PAUL M. BROWN JUNE 27» 1990

The basic electrical resonance principles pioneered by Nikola Tesla in the late 1800's are now being applied to a method of generating electricity from natural radioactive decay. Nucell, Inc. a subsidiary of Peripheral Systems, Inc.of Portland, Oregon, received a patent May, 1989, for their resonant nuclear oscillator (Figure 1). In general, the resonant nuclear oscillator is an LCR tank circuit tuned to oscillate at its self resonant frequency. Energy in excess of the operational losses is contributed from a radioactive source to the tank circuit through a phenomenon known as the Beta Voltaic Effect. Net electric current is then removed from the oscillator through an impedance matched transformer to deliver high frequency electricity in usable form to drive a load.

The Beta Voltaic Effect may simply be defined as the conversion of ionizing radiation to electrical energy by a material or combination of materials. Radiation that is absorbed in the vicinity of any potential barrier will generate separated electron-hole pairs which in turn flow in an electric circuit in response to the influence of the electric potential field.

Radioactive decay energy is several orders of magnitude greater than chemical energy. For this reason, this technology has promise of yielding low volume, low weight, high energy density power sources that will be economical for long unattended life with high reliability.

Devices for converting natural radioactive decay directly into electricity are nothing new (Figure 2). The Beta Cell was first demonstrated by Moseley in 1913 and over the years many types and methods have been developed. This technology has been made possible due to the electrical nature of alpha and beta disintegrations.

(Figure 3) The simplest form of nuclear battery is the Burke Cell. This method consists of a conventional battery and a conventional load connected by means of a radioactive conductor. If we inspect this arrangement we find that all of the power dissipated in the load is not drawn from the battery. And upon closer examination we find that a current amplification occurs within the radioactive conductor.

This phenomenon is known as the Beta Voltaic Effect and may be explained by referring to Figure 4. For the simple case of this example, we will set the radioactive source (any alpha or beta emitter) external and separate from a silver wire. Now the battery from Figure 3 provides an electromotive force (emf) across the wire and consequently, conduction electrons within the wire are set in uniform motion. By definition, electricity is measured in terms of the number of charged particles (electrons) moving past a point in a unit of time and we call this amperes.

The process by which a beta particle is absorbed, is such that the beta particle collides with the molecular structure of the copper knocking electrons free. This electron avalanche occurs until the beta particle (electron) effectively comes to rest. A single beta particle emitted from strontium-90 that is absorbed in copper will generate 80,000 ions in a distance of .030 inches. Now, as soon as these electrons are knocked loose, they effectively become free electrons in the wire, and as such these additional electrons are acted upon by the emf applied across the wire to give the avalanche electrons a uniform direction of flow, regardless of their incident angle. This increase in the number of moving charge carriers is measured in the real world as increased current. We also measure a reduction in the resistance of the wire, and an increase in its conductivity while the current is directly proportional to the voltage. In other words, the current goes up with an increase in voltage. This is basically attributed to the increased emf acting on a greater number of avalanche electrons.

(Figure 5) a cartoon representation of the basic beta voltaic converter is shown. Electrode A has a positive potential while Electrode B is negative with the potential difference provided by any conventional means. An electric field exists between the electrodes and we shall call this zone the junction. The junction between the two electrodes is thus comprised of a suitably ionizable medium exposed to decay particles emitted from a radioactive source.

In general, the introduction of ions from any source into an electric field will generate electricity in accordance with well-known physical or chemical principles and may be satisfactorily explained in terms commonly associated with the Beta Voltaic Effect. The energy contributed to such a circuit does not come from the ions themselves but rather from the work done on the circuit to generate the ions, known as the ionization potential of that particular material.

An amount of work must be performed on a neutral atom to remove electrons (ionize the atom). This work manifests itself as increased potential energy and may be utilized to do work before allowing the electron and ion to recombine.

Neither the electric field, the electrodes or the medium between the electrodes contribute any energy in the Beta Voltaic Effect. The energy is contributed by the ion generator whether this mechanism is chemical, electromagnetic or nuclear is irrelevant.

In other words, assume the conductor is irradiated with beta particles. As these particles penetrate the conductor, collisions occur with electrons in the lattice of the conductor resulting in the transfer of energy to these electrons and exciting them to a higher energy level in the conduction band.

Now we will look at how we apply this phenomenon to our device. Figure 6 depicts a basic LC tank circuit comprised of an inductor and a capacitor. Theoretically, if this LC circuit were superconductive, then an externally applied electric impulse would yield an LC oscillation that would continue to ocillate forever due to no losses in the system.

However, our LC circuit is not superconductive and the oscillation damps out due to the losses inherent to the LC tank. To minimize these inherent losses, we tune the circuit into resonance at the self-resonant frequency of the inductor.This causes the inductive and capacitive reactances to cancel leaving only ohmic losses (resistance).

(Figure 7) If we apply a radioactive source as part of the LC tank, then through every cycle of the oscillation of which current is flowing, that current gets amplified by an mount proportional to the activity of the source. All we need is an input of an amount of energy equal to the system losses to achieve a sustained oscillation. At this point, we have a self-driven oscillator what we call a Nuclear Powered Oscillator.

Any energy contributed to this oscillating LC tank must be removed and we accomplish this (Figure 8) by simply impedance matching a transformer which yields high frequency AC current to drive a load. In a nutshell, that is the principle of operation for the Resonant Nuclear Power Supply an LC tank circuit oscillating at its self-resonant frequency, driven by natural radioactive decay energy. Energy in excess of the operational requirements is removed through a transfer to yield electrical energy in usable form to drive a load.

Figure 9 depicts the starting method which involves the use of a high voltage source to charge the capacitor of the tank circuit, which is then discharged to ground through a Class C amplifier at a rate equal to the resonant frequency of the tank circuit. A spectrum analyzer is used to monitor the activity within the tank and once a clean oscillation is started, the high voltage power supply and Class C amplifier are removed; a process that takes a few seconds, then the power removed from the tank circuit is determined by measuring the voltage drop across a resistor of known value and double-checked by directly measuring the current delivered to the load.

The great attraction of radioisotope generators lies in the fact that isotope energy densities are several orders of magnitude greater than chemical energy density. However, the technology currently in use for radioisotope power generation is severely limited by its low efficiency, isotope limitations and heavy shielding requirements, while a resonant nuclear generator does not suffer from these limitations.

to accommodate the battery within the diameter of the drilling tubes. Another important potential market is to supply long life, electrical service to the sonar detectors which are in locations throughout the oceans of the world. The overall configuration in the case would probably be quite different. All of these possible applications need to be considered throughout the development phase.

Based on applications surveys, a design, development and testing program is being conducted on novel radioisotopic batteries that will be economical for long unattended life with high reliability, low weight and volume in the power range of 10 to 5,000 mW (e).

(Figure 10) Here we have the actual component layout of an early resonant nuclear power supply. We can see the radioactive source and its mount along with the primary inductor and matching transformer. The tuning capacitors are not shown.

(Figure 11) This is the actual wiring of the prototype shown in the previous slide. Although this generated electricity, it also demonstrated a frequency stability problem and showed signs of material degradation.

Economic studies indicate that a radioisotopic nuclear battery is economically competitive with chemical batteries for applications requiring lifetimes of over two years at remote locations where the expense of charging or changing batteries is significant. Applications where the inaccessibility after implantation is a consideration that leads to selection of nuclear batteries due to their superior reliability and life.

We have pursued several design variations and are currently working with an independent nuclear engineering firm. Our current program will generate engineering data in the coming months. Of course any alpha or beta emitting isotope will work while a design variation also allows the use of gamma sources. We have experimented with cesium, strontium, radium, krypton, tritium, promethium and probably some others. All these sources have worked, however, for personnel safety and application considerations we are currently planning to use krypton-85 as the fuel source, although strontium-90 is also a good candidate.

Large quantities of krypton-85 are contained in stored power-reactor fuels and about 1 MegaCurie per year is available from processed fuel. It is estimated that 42 MegaCuries of krypton-85 could be obtained from existing inventories in power-reactor fuels with the content in spent power-reactor fuels at about 8,500 Curies per ton.

Of the many radioactive isotopes generated by the fission of uranium, krypton-85 has many unique properties of which the most Important is its advantage of being environmentally the most acceptable radioisotope available for power production.

Preliminary data suggests that energy densities on the order of .25 watt per cubic centimeter is achievable.

Market surveys have been conducted by the nuclear industry in the past and the conclusion has been that there is a need for long-life radioisotope nuclear batteries. Of course, economic and logistical factors must be considered for comparison (Figure 12).

Obviously the physical size and shape of the radioisotope batteries will need to be related to the intended applications. For example, in oil and gas well drilling, there is an increasing benefit in continuously measuring and monitoring geo-physical data from the bottom of the hole. Under these circumstances it would be necessary

References:

(1) Brown, Paul. TI IE MORAY DEVICE AND THE HUBBARD COIL WERE NUCLEAR BATTERIES in Magnets In Your Future Magazine, Vol. 2, No. 3, March 1987.

(2) Brown, Paul. RESONANT NUCLEAR POWER SUPPLY

in Raum & Zeit Magazine,Vol. 1, No. 2, Auqust-September, 1989.

(3) Brown, Paul. American Nuclear Society 1989 Winter Meeting, San Francisco, California, November 26-30,1989, RESONANT NUCLEAR BATTERY MAY AID IN MITIGATING THE GREENHOUSE EFFECT

(4) Brown, Paul. American Nuclear Society Annual Meeting, June 10-14,1990, Nashville, Tennessee, THE BETA VOLTAIC EFFECT APPLIED TO RADIOISOTOPIC POWER GENERATION.

For More Information Contact;

Paul Brown Nucell, Inc.

12725 S.W. 66th Avenue, Suite 102 Portland, Oregon 97223 503/624-8586

NUCELL, INC. A SUBSIDIARY OF PERIPHERAL SYSTEMS, INC.

United States Patent i-s;

Brown

4,835,433 May 30, 1989

(54] apparatus for direct conversion of radioactive decay energy to electrical energy (73] Inventor: p»ul M. Brown, Boise, Id. (73) Assignee: Nucell, Inc„ Portland. Orcg

).40YI)0 11/1961 Burke 3.5)0.316 9/1970 Burke

3.362.613 2/1971 Adler

3.944.4)1 J/1976 Hursene

4.419.269 12/1914 Edling el

310/305 310/391 310/304 310/301 136/202 376/320

Related U.S. Application Dau

376/320

310/304, 305; 136/202

References Cited u.s. patent documents

2,344.223 4/1951 Linder

2.712,097 6/1933 Aiwaner

3.290,322 12/1966 Giaell

Primary Exominir—Deborah L Kyle Auisiant Exomtntr—Daniel Waul AHornty. Àgini. or Firm- Leslie G Murray 157) ABSTRACI"

A nuclear battery in which the energy imparted io radioactive decay products during the ipontaneoui disintegrations of radioactive material is unlired to sustain and amplify the oscillations in a high-Q LC tank circuit is provided. The circuit inductance comprises a coil wound On a core composed of radioactive nuclides connected in series with the primary winding of a power transformer The core is fabricated from a mature of three radioactive materials which decay primarily by alpha emission and provides a greater flu* of radioactive decay products than the equivalent amount of a single radioactive nuclide

10 Claims, 4 Drawing Sheets

Figure 1

Source

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