Patent Abstract:
A method and apparatus for collecting and storing the energy emitted by radioisotopes in the form of alpha and or beta particles is described. The present invention incorporates aspects of four different energy conversion and storage technologies, those being: Nuclear alpha and or beta particle capture for direct energy conversion and storage, fuel cells, rechargeable electrochemical storage cells and capacitive electrical energy storage.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 13/851,890 filed Mar. 27, 2013, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The idea of using radioactive materials as direct power sources for applications requiring long-lived power sources has been investigated for many decades. Nuclear power sources for deep space probes have been used on many NASA programs especially those that last for decades and where the probes will not have sufficient sunlight for solar panels to operate. Nuclear Batteries, also called atomic batteries, have been developed that attempt to exploit the heat or thermal energy of the radioactive materials as well as the alpha and beta particle emissions energy through various means. Typically these devices tend to be large in comparison to typical electrochemical batteries and also tend to suffer from the emissions of high energy particles including alpha, beta, gamma and neutrons which create human health risks. Besides space probes, small nuclear power sources have been successfully used in devices such as pace makers and remote monitoring equipment. 
         [0003]    One area of much research has to do with the direct conversion of beta emissions, i.e. electrons, emitted from radioisotopes that are targeted on a semiconductor material to develop electron-hole pairs and thus generate an electrical current in the semiconductor. All of these devices suffer from very low efficiencies due to the poor electron capture cross section of the designs as well as the semiconductor material itself. This is the same phenomenon that solar cells continue to suffer from even after decades of work and hundreds of billions of dollars of investment. 
         [0004]    Researchers have recently begun investigating nanotechnologies with which to implement nuclear power sources. Some of these include the development of micromechanical devices that vibrate or rotate in response to charge build up within the semiconducting materials. 
         [0005]    The underlying reason for pursuing the development of nuclear batteries is the much wider goal of developing long lasting, low cost power sources. Along these lines, there are many other fields of research that are producing some interesting and potentially viable power sources. In particular, fuel cells and new electrochemical battery technologies look particularly promising for small, low cost, high density and long-lived power sources but none come close to the energy density and longevity that nuclear power sources offer. 
         [0006]    Prior art describes four basic methods of converting radioisotopes into useable energy sources. Three of these require a double conversion process wherein the radioactive sources are used to first generate heat, light or mechanical energy which is then converted into electrical energy. These multiple conversion processes have extremely low efficiencies which puts them at a distinct disadvantage to compete with the fourth method which is referred to as direct conversion. 
         [0007]    Of the direct conversion methods, the two that are the most studied are the semiconductor PN junction conversion and the capacitive charge storage conversion. The semiconductor conversion processes, also known as betavoltaics, employs semiconductor technology that suffers from device degradation and very low efficiencies. The capacitive charge storage devices have problems with large size and very high voltages that can reach hundreds of thousands of volts that create materials challenges that can withstand such high voltages. These problems are magnified as the devices are scaled down. 
         [0008]    A common problem for all of the prior art is that the amount of energy that can be extracted from the radioactive material is a very low level and at a consistent output which doesn&#39;t provide a practical means to support real world applications that demand varying amounts of power at different times. 
         [0009]    Of the most relevant descriptions of a nuclear batter disclosed in prior art, Baskis, 5825839, describes a direct conversion nuclear battery utilizing separate alpha and beta sources isolated by an insulating barrier and two charge collector plates, one to collect the negative beta particles and a another plate collect the alpha particles. The two plates become charged and thereby storing the energy in the form of an electric potential the same as a capacitor stores electrical energy in the form of positive and negative charges on parallel plates. This approach utilizes the balanced alpha/beta charge approach as the present invention, but for completely different purposes. In the Baskis disclosure, a load place across the “battery” allows electrons to flow from the negative charged plate to the positively charged plate that is saturated with alpha particles. The recombination of the electrons and the alpha particles is said to produce helium gas which is vented out of the cell. However, this description does not address the recombination of “free” electrons in the metal plate combining with the alpha particles producing He gas directly. However the net effect is the same, the positive plate will become increasingly positively charged by the alpha particles producing a stored electric potential across the device. 
         [0010]    The preferred embodiment of the present invention also suggests the use of balanced alpha and beta charges for greater efficiencies, however, such a requirement is not necessary for it to operate. Additionally the present invention can store the energy of the alpha and or beta particles in chemical energy form as a chemical battery as well as in electric potential energy as in a capacitor, as described in alternative embodiments. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    The present invention incorporates aspects of four different energy generation and storage technologies, those being: Nuclear beta and/or alpha direct conversion, fuel cells, rechargeable electrochemical storage cells and capacitive energy storage. In the present invention, a radioisotope, or a mixture of radioisotopes, that emits beta and/or alpha particles is used as the primary energy source while an electrochemical cell is used as both a secondary energy source as well as an energy storage mechanism and a capacitor that may be used as a primary storage device as well. 
         [0012]    This disclosure illustrates the core concepts for the construction and manufacture of the device but by no means limits the actual materials to only those used as examples and discussed herein nor the embodiments described. For example, almost any radioisotope can be used as the primary fuel source for this invention but those that are, at this time, considered safer, more optimal or more readily accessible are more desirable, especially for devices that could be used for equipment that will be in close proximity to humans or animals. As research continues and future advanced occur, it may become feasible that other radioisotopes may be well suited for use in this device and the following discussions are by no means intended to limit the invention to only the specific materials used or discussed herein. This is true for the materials used including those for the electrochemical and capacitive storage materials as well. 
         [0013]    Additionally, no limitations to the embodiments of the described invention are to be inferred. This disclosure is to be interpreted in its broadest sense as to any materials that can be used as well as to the physical embodiments in which the concepts can be applied. For instance, there are hundreds of radioactive materials that can emit alpha and or beta particles and electrochemical batteries and capacitors can be built in an unlimited number of shapes, sizes, storage capacity, energy densities or materials. There are also many rechargeable battery chemistries that can be used in said present invention and no limitations as to the type of rechargeable battery or chemistry that can be used to implement such a device is implied. 
         [0014]    Any radioisotopes or combination of radioisotopes that emit alpha and or beta particles can be used for this device. However, because the device takes advantage of both the positive charges of the alpha particle and the negative charge of the beta particle, to generate dc current directly as well as to provide a charging mechanism for the electrochemical cell, radioisotopes that produce both particles are expected to produce greater energy density and efficiencies than isotopes that produce only alpha or beta particles, however any combinations of radio isotopes or individual radioisotopes can be used. Radioisotopes that produce low energy alpha and or beta particles are particularly useful in this application since the emissions can be contained within the structure itself, thus eliminating the health issues of ionizing gamma and or neutron radiation. Isotopes that produce gamma rays and high-energy neutron are less desirable due to their associated health risks, and the inability to completely contain these emissions within the power cell itself. However, the power cell can be adapted for their use for certain applications where these issues are not a concern, for instance in generating electrical energy from nuclear waste products stored in long term storage facilities. In this case, the hazardous material is already placed in secured facilities where the high-energy emissions cannot harm persons or the environment. Using any or all available radioisotopes to generate electrical energy would be a good use for this invention. Additionally, space probes could, from a human safety standpoint, use any radioisotope material. 
         [0015]    While the invention has been described with reference to some preferred embodiments of the invention, it will be understood by those skilled in the art that various modifications may be made and equivalents may be substituted for elements thereof without departing from the broader aspects of the invention. The present examples and embodiments, therefore, are illustrative and should not be limited to such details. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  illustrates a cross-section of a device according to a preferred embodiment of the invention. 
           [0017]      FIG. 2  illustrates a stacked cell configuration. 
           [0018]      FIG. 3  illustrates an internal self-recharging process. 
           [0019]      FIG. 4  illustrates an attachment and use of an external DC charge circuit. 
           [0020]      FIG. 5  illustrates a discharge process. 
           [0021]      FIG. 6  illustrates an embodiment of an implementation in a form of a standard cylindrical battery that is commonly available. 
           [0022]      FIG. 7  illustrates a layered approach of placing an amorphous semiconducting material capable of producing large amounts of electron-hole pairs through bombardment of alpha or beta particles. 
           [0023]      FIG. 8  illustrates the use of collector plates in or near the amorphous semiconducting material to aid in the collection of electron-hole pairs before they can recombine. 
           [0024]      FIG. 9  illustrates the use of a mixture of radioactive material and amorphous semiconducting material in the cell. 
           [0025]      FIG. 10  illustrates the cascade of electron-hole pair production within a mixture of the radioactive material and the amorphous semiconducting material. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    For the following discussion, refer to  FIG. 1 . The device  10 , comprises a rechargeable electrochemical cell  20 , such as a Lithium Ion cell, which may be comprised of a cathode plate  19  such as aluminum, a Li ion capture material  18  such as LiCoO2 (or LiMnO2, or others), an electrolyte material  17  such as a lithium salt dissolved in organic solvent with a semipermeable membrane  16  separating the anode and cathode sides of the cell, a carbon anode  14  with an plate  13  such as copper, a layer of radio isotope material or a mixture of radio isotope materials  12  which emit alpha and or beta particles, with a bonding (agent not shown) and a proton exchange membrane layer  11  that is comprised of a highly negatively charged material, and a dielectric insulating layer (not shown). These layers can be rolled up to produce a typical cylindrical battery device, referred to in the industry as a “jelly roll,” and shown in  FIG. 6 , or stacked on top of each other in many layers to produce irregular shapes and sizes that would be used in consumer electronic devices as shown in  FIG. 2 . While the secondary battery technology described herein happens to be a Li-Ion type battery, any battery storage technology compatible with this invention can be used, and a person skilled in the art of battery chemistry and technologies could easily adapt any battery technology to be useful in this invention. 
         [0027]    The amount of radioisotope material that would be needed in a particular power cell would depend upon the activity level of the particular material used and the amount of energy that the power cell would need to provide for a specific application. 
         [0028]      FIG. 2  shows a cross section a stacked cell implementation of the invention as the cells would exist relative to each other. This orientation would exist whether individual cells are stacked on top of each other or a long single cell was rolled up into a cylindrical shape. In  FIG. 6 , the layers of the cell would be rolled up upon themselves to create a cylindrical form similar in size and shape of common commercially available batteries such as “AA”, “AAA”, “C” and “D.” Of course any shape or size can be constructed by stacking the layers shown in  FIG. 2 . When stacking layers, the PEM (Proton Exchange Membrane) layer  11  would be located between the radioisotope material layer  12  and the cathode plate  19 . Also note that the cathode plate  19  and the anode plate  13  are offset with respect to each other and with respect to the PEM layer  11  so as to prevent shorting the cells when they are assembled as well as to allow each cathode plates  19  to be connected together on one end or side of the cell and the anode plates  13  to be connected together on the other end or side of the cell. This also provides a means to connect the anode and cathode to the cell contacts for external connections. 
       Theory of Operation 
       [0029]    Refer to  FIG. 3  for the following discussion. A key aspect to the invention is the adoption of a proton exchange membrane  11  (PEM) similar to that used in fuel cell technologies. A common type of material used for this application is Nafion. There are a number of proton exchange membranes available that can be used in the present invention. In fuel cells, the PEM is a highly electronegative porous material that allows the positive charged “protons” to cross the membrane boundary between the anode and cathode while repelling the disassociated electrons and forcing them to flow around the cell, through an external circuit. These PEM characteristics are exploited in the present invention to allow the doubly positively charged alpha particles  23 , which are approximately the same size as methanol “protons” to pass through the PEM material  11  and collect in the cathode plate  19 , while forcing the beta particles  22 , i.e. electrons, to flow to the anode plate  13  and collect there. The positive charges carried by the alpha particles  23  and captured by the cathode plate  19  and the negative charges carried by the beta particles  22  and captured by the anode plate  13  will migrate to their respective cathode  18  and anode  14  regions causing the cell  10  to store the charges. These charges would then cause the lithium ions  20  to migrate from the cathode  18  through the electrolyte region  17 , across the separator membrane  16 , further across the solid electrolyte interphase (SEI) layer  15 , which is formed upon first charging, and finally to in situate themselves, intercalate, within the carbon layers of the anode  14 , thus completing the charging cycle for a pair of alpha  23  and two beta  22  particles. 
         [0030]    Referring to  FIG. 5 , when an electrical load is placed across the anode plate  13  and cathode plate  19 , an electric circuit would be completed causing electrons from the anode  14  to migrate to the anode plate  13 , through the external circuit  26  and returning to the cell at the cathode plate  19 . The ideal cell would be achieved when amount of radio isotopic material  12  and the external electrical load  26  were balanced where the total electrical current emanating from the radioisotope region into the anode plate  19  and cathode plate  13  were to equal the amount used by the electrical load  26 . This is an ideal condition that is unlikely to ever be achieved. Normally electrical loads have varying power requirements and this is where the rechargeable electrochemical storage portion  20  of the cell  10  plays it role. It will provide additional power to the load  26  when it is needed and it will store the excess energy coming from the radio isotope material  12  for later use. 
         [0031]    If an electrical load were connected across the anode plate  13  and cathode plate  19 , an electric circuit would be completed causing electrons from the anode  14  to migrate to the anode plate  13 , through the external circuit  26  and returning to the cell at the cathode plate  19 . The ideal cell would be achieved when amount of radio isotopic material  12  and the external electrical load  26  were balanced where the total electrical current emanating from the radioisotope region into the anode plate  19  and cathode plate  13  were to equal the amount used by the electrical load  26 . This is an ideal condition that is unlikely to ever be achieved. Normally electrical loads have varying power requirements and this is where the rechargeable electrochemical storage portion  20  of the cell  10  plays it role. It will provide additional power to the load  26  when it is needed and it will store the excess energy coming from the radio isotope material  12  for later use. 
         [0032]    Referring to  FIG. 4 , as with any secondary electrochemical cell, the present invention can be recharged by means of an external charging circuit  25  placed across the cathode plate  19  and anode plate  13 . The charging circuit  25  injects electrons  21  into the anode plate  13  which migrate into the anode carbon layer  14  and speed up the lithium ion battery charging process as shown in  FIG. 3 . 
         [0033]    During discharge, the beta particles  22  (electrons) emitted by the radio isotope layer  12  will flow directly through the anode plate  13  to power the external load  26  while the alpha particles will accumulate at the anode, completing the circuit. The current developed from the radioisotope material  12  will power the load reducing the draw from the stored energy of the secondary electrochemical battery cell  20 . However, when the current drawn by the load  26  is less than the current developed by the radioisotope material  12 , then the excess current will charge the secondary battery cell  20 , thus acting as a charging circuit for the secondary electrochemical storage battery  20 , the same as if the secondary battery were being charged from an external charging device  25 . 
         [0034]    Because of the affinity of the anode  14  to accept electrons and the highly electronegative characteristics of the proton exchange membrane (PEM)  11 , the beta particles  22  are attracted to the anode plate  13  and collect there developing an overall negative charge on the plate which is transferred to the anode carbon layer  14 . The increasingly negatively charged carbon anode  14  attracts positive lithium ions  20  from the electrolyte  17  causing the migration of the lithium ions  20  from the lithium metal oxide cathode  18 . At the same time, the alpha particles  22  are attracted by the overall negatively charged proton exchange membrane (PEM)  11  and migrate towards it. The PEM  11  doesn&#39;t have any binding sites for the alpha particle and its physical properties allow the alpha particles  22  to pass through it to the cathode plate  19  where they are able to bind with the cathode plate  19  and transfer their positive charges to the cathode plate  19 , thereby oxidizing the cathode layer  18  and liberating more lithium ions  20  to migrate across the cell to the anode  14 . 
       Alternative Embodiments 
       [0035]    Since the radioisotope material  12  continually emits alpha and/or beta particles  22  and  23 , at some point the battery will become fully charged with all Lithium ions  20  being intercalated within the carbon material of the anode  14  but the radioisotope material  12  will still be developing an electrical potential. Some of this unused electrical potential can be stored in an integral super capacitor (not shown in drawings) surrounding the entire battery device but inside the enclosure  31 . 
         [0036]    The super capacitor is created by connecting one thin metal plate (not shown in drawings) to the anode plate  13 , another thin metal plate (not shown in drawings) attached to the cathode plate  19  and a thin insulating material (not shown in drawings) separating said plates. However, depending upon the total energy storage capacity of the device and the system load demands, eventually one of two conditions will occur. 
         [0037]    Either the cell will be completely depleted or it will become fully charged. In the event of a full charge within the electrochemical cell and any integral capacitor of the battery, the excess energy will have to be exhausted as heat. This excess energy is most effectively released through a resistive material (not shown in drawings) around the outer surface of the cell but inside the protective metal enclosure  31  or incorporated as an integral part of said enclosure  40 , so as to radiate off excess energy as heat into the surrounding environment. A built-in charging and discharging control circuit can be used to control the excess energy bleed off. 
         [0038]    A second situation exists where the device becomes completely discharged and cannot provide sufficient power for the intended load. At this point, the equipment which is powered by the device is turned off or the power cells are changed out for fresh cells. In either circumstance, the radioisotope will recharge the cell. Current lithium battery technologies limit discharge to about  40  percent. A deep discharge will damage the battery and limit its lifespan. This situation is prevented by a charge control circuit which will prevent battery damage due to overcharging or over discharge. 
         [0039]    Alternatively, a standalone self-charging nuclear capacitor is made by applying a thin layer of the radio isotope to one side of a thin metal foil then a layer of the PEM material over the radio isotope combined with a binding material followed by the second metal foil layer and finally a dielectric membrane is placed on the top of the second foil layer. These layers are then rolled up so that the two metal layers are separated by the dielectric membrane. The metal foil layers are chosen just as in any electrolytic capacitor so that the plates have a propensity to attract and store positive or negative charges. An example would be aluminum and tantalum foils. 
         [0040]    As described above, this capacitor can be implemented directly in the nuclear rechargeable electrochemical power cell by adding the capacitor layers sandwiched in the radioisotope layer. If the cell design characteristics are chosen to incorporate a high voltage capacitor to store more power, a voltage regulator would be needed to regulate the charge voltage for the electrochemical cell to protect it from damage from over charging and over voltage. A large amount of energy can be stored within this super capacitor that can be used for loads that demand very high currents for very short periods of time or if regulated can produce lower voltages for longer periods of time, or even other voltages than that of the battery. 
         [0041]    Since alpha particles possess a positive double (+2) charge, they are easily deflected by electric or magnetic fields. The electric field generated by the cell construction, with or without the high voltage capacitor may be effective in driving the alpha particles towards the cathode collector plate and thus, increasing efficiency. Similarly, the addition of a magnetic material layer that creates a magnetic field that directs the alpha particles towards the cathode may also be effective in increasing efficiency. These same phenomena may also serve to push the electrons towards the cathode as well. 
         [0042]    The amount of radioactivity emissions from materials that are generally considered “safer” than other radioactive materials tend to be too low powered for use as a direct energy source for present day electronic devices. The goal of designing a high energy, long lasting and safe nuclear power source is confounded by fundamental material limitations where the amount of energy emitted is roughly inversely proportional to the half-life of the material. That is, the higher the energy output, the shorter the half-life. The goal is to develop devices that can last many years to several decades that can also produce the sufficient output power to run electronic devices or system without undue risks to human life or the environment. 
         [0043]    Research into betavoltaics using P-N junctions in silicon and other semiconductor materials has been focused on creating electron-hole pairs near the P-N junction of the semiconductor material. These electron-hole pairs develop a voltage and current across the P-N junction when a beta particle is ejected from the radioactive material and travels through the semiconductor material. Much research has been spent on building 3D structures within the semiconductor materials to hold the radioactive material in such a manner that would capture as many beta particles as possible to produce the most electron-hole pairs as the beta particle travels through the semiconductor material. Some research suggests that as many as 2000 electron-hole pairs can be generated with each beta particle emitted from a tritium source. There are a couple major problems with this approach. The first being that these techniques require expensive silicon wafer production facilities and their associated high costs for the base semiconductor wafers. The second is that the semiconductor materials deteriorate from lattice destruction caused by the kinetic energy of the beta particles. These devices tend to fail in a relatively short period of time (months to a few years) from even the lowest energy beta emitters. Destruction of the P-N junction and semiconductor lattice structure renders the already low efficiencies of this method to steadily decrease over time. 
         [0044]    To increase the electron-hole generation in the present invention, a layer of amorphous semiconducting material, or any other material found to be generous electron-hole pair generator, can be applied on either or both sides of the radioactive source material that will generate a cascade of electron-hole pairs as the alpha and or beta particles travel through it. See  FIG. 7 . Since the present invention doesn&#39;t rely on a P-N junction to develop a voltage differential across the cell, very inexpensive amorphous semiconductor material of various kinds can be used as the electron-hole generation material. The electric field developed by the cell chemistry will naturally draw the electrons towards the anode plate while the holes will be drawn to the cathode plate. Recent research has shown very low cost amorphous metal oxide materials to be effective electron-hole generators as well. Additionally, since amorphous materials contain neither a P-N junction nor a regular lattice structure, electron-hole pairs can be generated for long periods of time without the concern of the material experiencing structure breakdown. A secondary benefit is that these materials are very inexpensive. 
         [0045]    Research has also shown that the effective electron-hole generation capabilities of low energy beta emitters such as tritium extend only a few hundred microns deep into a semiconductor material. Two of the main processes that contribute to the inherent low efficiencies of the semiconductor P-N betavoltaic approach are that there is a high rate of reabsorption of the emissions from the bulk radioactive material and the recombination of the electron-hole pairs in the semiconductor material. The rate of reabsorption is proportional to the thickness of the bulk material used in the cell. If the radioactive material is thicker than a few hundred microns then the rate of reabsorption increases with the additional thickness since only those emissions close to the surface of the material are likely to escape to be used to generate power. On the other hand semiconductor P-N junctions that are deposited on the surface of a semiconducting chip structure are unable to capture many of the electron-hole pairs generated at deeper layers of the semiconductor because the electron-hole pairs have a greater chance of recombining within the bulk semiconductor body before they can migrate through it and combine at the anode and cathode to contribute to the cell&#39;s power output. 
         [0046]    By depositing the radioactive material in a very thin layer, something on the order of hundreds of microns, the reabsorption can be reduced and almost eliminated since most of the emissions will be close enough to the surface of the material to escape into the surrounding materials where they can be captured and used for power generation. Since the distance that a particle will travel through a solid material depends upon its energy as well as the material it is traveling through, the optimal thickness of the radioactive material layer will probably be determined based upon these factors for various cell chemistries. This thin layer approach is the optimum structure for a radioactive material based power cell. When structured in this fashion, essentially all the emissions from within the radioactive material will be able to escape the bulk material and thereby limit the reabsorption effects. This is because the radioactive source material layer would be so thin that most of the emissions would have a high probability of escaping from the large surface areas of the layer and only the relatively few emissions that occur along the axis of the layer would have a high probability of recombination. See  FIG. 7 . By placing layers of a semiconducting material  45  on one or both sides of the radioactive material layer, the kinetic energy of the escaping alpha and beta particles can be used to generate electron-hole pairs in the semiconducting material. This is described in greater detail below. 
         [0047]    Referring to  FIG. 10 . When alpha or beta particles are spontaneously emitted from the radioactive source material, they will invariably run into other atoms and release some of their kinetic energy to those atoms. A small percentage of these interactions result in an electron of the target atom being knocked free. The freeing of an electron  49  from an atom results in the atom having an overall positive charge. This is referred to as a “hole” and is denoted as “h + ”  50 . This process is shown in  FIG. 10 . The physical interaction of the alpha particle  47  and the beta particle  48  within the semiconducting material can result in the formation of an electron-hole pair  51 . If the electron  49  is knocked free from the target atom so that it cannot immediately recombine with the positive hole  50  then the two charges have a chance to migrate across the cell and be absorbed by the anode  13  and cathode  19 . If the electron is immediately recaptured by the target atom from which it was liberated, or another atom with a positive charge, then the two charges will cancel out and no useful energy can be obtained. This is known as recombination. Since the amount of energy needed to free an electron in the semiconducting material is much much lower than the energy of the impinging alpha or beta particle, many electrons can be liberated and many holes formed within the semiconducting material before the particle&#39;s kinetic energy is absorbed. This process creates a cascade of electrons  49  and holes  50  from a single radioactive particle.  FIGS. 7, 8 and 9  show variations of cell construction that can be used to optimize the electron-hole generation and capture based upon various cell chemistries and radioactive source particle energies.  FIG. 10  shows the electron-hole generation that occurs within a mixture of radioactive source material and an amorphous semiconducting material. In this application, shown in  FIG. 9 , the overall thickness of the mixture would necessarily need to be much thicker than the very thin layer of the pure radioactive layer described earlier in order to increase the probability that the particles will interact with many semiconductor material atoms to generate the greatest amount of electron-hole pairs  51 . The down side to a thicker layer is the higher probability of recombination as the electrons and holes migrate across this layer. Experimentation with the radioactive source material and the semiconducting material will need to be done to optimize the layer  46  thickness. The optimal thickness of  46  will, of course, depend upon the nature of the materials used. 
         [0048]    Referring back to  FIG. 7 , with a thin layer of amorphous semiconducting material  45 , or any other material found to be a generous electron-hole pair generator, on one or both sides of the radioactive material layer  12 , a single alpha or beta particle emission can be amplified hundreds or even thousands of times through interaction with the amorphous semiconducting material as shown in  FIG. 10 . The resulting electrons  49  and holes  50  will migrate across the semiconductor and radioactive material regions towards the appropriate cell plates. The longer migration path will increase the probability that the electrons and holes recombine before they reach the opposite plate. 
         [0049]    The thickness of the semiconducting layers  45  will require experimentation to determine the optimal thickness. Two competing processes will tend cancel each other out. First, if the semiconducting layer is too thin then too many of the alpha particles  23  and beta particles  22  will pass through the layer without creating a cascade of electron-holes  51 . Therefore, the thicker semiconductor layers  45  are, the greater the capture rate and the greater the electron-hole generation. Competing with that process is the rate of recombination which increases as the distance that the charges have to travel to reach the anode and cathodes increases. Just as in a betavoltaic semiconductor direct conversion device, a too thick amorphous semiconductor material layer will allow too many of the electron-hole pairs to recombine within the material itself canceling out their electrical usefulness in the cell. 
         [0050]    Another issue to consider in cell construction are the electrical characteristics of the radioactive source material. The electrons  49  or holes  50  may not be able to migrate across the radioactive material layer either because the radioactive material may itself be a natural electrical insulator which would inhibit charge migration or perhaps it may have metal characteristics that promote the recombination of the electrons  49  and holes  50  as they migrate from the semiconducting material regions  45  across the radioactive source material region  12 . A solution to this problem, see  FIG. 8 , could be to place porous collector plates  41  &amp;  42  in or around the semiconducting material regions  45  with collector plate  41  connected to the anode  13  through connector  43  and collector plate  42  connected to the cathode  19  through connector  44 . The collector plates  41  &amp;  42  and associated connections  43  &amp;  44  would provide a direct path for the charges to reach the cell anode  13  and cathode  19  and would reduce the distance that they would have to travel through regions  12  &amp;  45  which in turn would reduce the probability of recombination and eliminate the potential electrical characteristics issues of the radioactive source material. In this embodiment the collector plate  41  would allow the alpha particles  47 , and the holes  50  to pass through it to collect on the cathode plate  19 , while collecting the beta particles  48  the electrons  49  while also providing a low impedance path through connection  43  to the anode  13 . Conversely, collector plate  42  would allow beta particles  48  and electrons  49  to flow through it to the anode  13  while collecting the alpha particles  47  and the holes  50  while also providing a low impedance path through connection  44  to cathode  19 . 
         [0051]    See  FIG. 9 . Yet another embodiment would be to mix the amorphous semiconductor material with the radioactive material, as described above, and applying the mixture in a thin layer  47  that would allow the alpha and beta particles along with the electron-hole pairs they create to migrate across this region without a great probability of recombination or reabsorption could be a very effective technique. In this case, the alpha and beta particles  47  &amp;  48  respectively, along with the electron-hole pairs  50  generated within the amorphous semiconducting material would migrate to the appropriate plates under the influence of the cell&#39;s electric field, thus producing far greater output capacity than the alpha and beta particles alone. One potential benefit to this embodiment is that the semiconducting material would work to counteract the electrical characteristics of the radioactive source material. The semiconducting material would act as a low impedance path for radioactive source material that is a natural insulating material but would have an insulating effect on those radioactive source materials that are metallic in nature and therefore good natural electrical conductors. The net result would be a beneficial semiconducting medium that produces cascades of electrons  49  and holes  50  for each alpha particle  47  and beta particle  48 . Again, experimentation to determine the optimum thickness of layer  46  and the relative amounts of the radioactive source material and semiconducting material would be required. This layer&#39;s characteristics will also be greatly influenced by the materials used. 
         [0052]    While the terms amorphous semiconductor and semiconductor are used to describe a preferred embodiment of this technique, it is not to be interpreted to be the only kind of material state that can be used to generate the electron-hole pairs. In fact, any mater or materials that produce electron-hole pairs when bombarded with radioactive particles whether amorphous, crystalline, polysilicon, nano-materials or any other forms, can be a suitable potential source material for the present invention. 
       External Charging 
       [0053]    The inherent nature of the self-recharging battery does not preclude the capability of a fast charging in an external charging device. A nuclear battery of this design can be quickly charged by means of inserting it into an external battery charger, similar to existing battery charging devices using standard charging techniques. 
         [0054]    A self-monitoring circuit to indicate to the user the level of charge that the cell has at any given time can be incorporated into the device. Since the radioisotope would continuously charge the device, especially when it is not in use, power cells using this technology can be swapped out of equipment, set aside, and they will recharge automatically. Alternatively, they could be charged more quickly by an external charger device. The charge indicator would be powered by the device directly and would let the user know how much power is available at any given time. 
         [0055]    An electronic circuit that could control the internal and external charging and discharging characteristics of the battery could be incorporated as a safety/security aspect of the device. This circuit could be used to control the total charge of the battery as well as to disable the battery recharge system to prevent automatic self-recharging or external recharging. This functionality would be useful in a battlefield situation where the battery may be lost or stolen. In such a situation, the battery could be rendered useless, or at least prevented from recharging. Such a system can be implemented by incorporating a built in electronic chip/circuit that would enable or disable recharging or it could force discharging of the battery under specific conditions through the resistive load material used to bleed off excess power. For instance, such a condition may be where a warfighter would carry a tiny wireless control device (perhaps built into some other equipment) that would communicate with the battery controlling its functionality. Should the battery become lost or stolen and unable to communicate with some approved remote control device, the battery could automatically render itself useless, either by discharging or not allowing itself to be recharged externally or internally, thus rendering it useless to anyone but those with the correct controller devices. 
         [0056]    This same wireless control circuit could be used as a locator beacon that could be activated under any number of predefined conditions such as tampering or destruction of the cell in an attempt to obtain the nuclear materials. 
         [0057]    While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Technology Classification (CPC): 7