The short and unpredictable nature of the conventional chemical batteries, along with the frequent replacements that they require, has created an acute need for a reliable, longer-lasting and rugged source of energy. Moreover Radars, spacecrafts, interstellar probes and other advanced communication devices require much larger power than that can be met by conventional energy sources. The solution to long term energy source is the nuclear powered batteries which have a life p of few decades and can pack in energy densities thousands of time greater than conventional battery sources.
Hence, there is an urgent need to harvest enormous amount of energy released naturally by the tiny bits of radioactive material. Unlike conventional nuclear power generating devices, these batteries do not rely on the fission or fusion reactions and do not generate any radioactive material as by-product. They promise clean, safe, reliable and almost endless energy without any drop in its yield or efficiency during its entire life p-which runs up to minimum of 10 years. They are generally used as power sources in unmanned and unmaintained locations requiring energy for longer durations.
Nuclear batteries are not only going to replace conventional batteries, chargers and adapters but also present innovative means of powering portable devices. The nuclear battery technology is geared up to make way into commonly used day to day product like cell phones, laptops, automobiles etc. Surely it is battery of future. INTRODUCTION In this day and age of miniaturization the size of electronic circuitry has been diminishing at a astonishingly dizzying pace but the batteries that power these devices are not keeping up with them.
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The world of tomorrow that the technology manifests will be a very small one and we will need smaller batteries to power it !! Be it our personal laptops or cell phones, batteries still occupy a significant portion of the volume. The reason being the batteries are still nothing more than cans of chemicals like they were two centuries ago. They have not undergone any significant change in their functionality since Italian physicist Alexandaro Volta demonstrated flow of lectric current between two conductors by alternating discs of zinc and copper with pieces of cardboard soaked in brine. Many systems ideally (especially those in remote locations) have to operate for long periods, and it is not always feasible to recharge or replace their batteries. Now, with technology ushering in new era of miniaturization where MEMS (Micro Electrical Mechanical System) are gaining widespread popularity and are increasingly being used for a multitude of applications, they lack a durable onboard power supply. Batteries are at a critical juncture here!!
MEMS are finding increasing applications in everything from sensors in car that trigger an alarm to injectible drug delivery system to environment monitoring ‘Smart Dust’ but they lack a long lasting on-device power source. To work around this power block, researchers have found an intriguing way: by harvesting the huge amount of energy released by radioactive material. Although several sources of energy could be used to supply this needed power (solid, fossil fuel) by these MEMS based systems but nuclear batteries are fast becoming a popular option in terms of power density and lifetime.
For example A tiny speck of radioisotope like nickel-63 can generate enough energy to power these MEMS for decades. These nuclear micro batteries have energy at densities at thousand times greater than the Lithium ion batteries. So with these miniature machines really hitting their stride, we’ll need smaller, reliable and longer lasting battery sources! To clear the common misconception, nuclear power sources are not miniature nuclear reactors and they do not involve any fission or fusion reactions.
In these power sources we use specific isotopes which emit particles that are blocked by the layer of dead skin that covers our bodies. They penetrate no more than 25 micrometers in most solids or liquids, so in a battery they could safely be contained by a simple plastic package! TechnologyEnergy Density (milliwatt-hour /milligram) Lithium ion in a chemical battery0. 3 Methanol in a fuel cell3 Tritium in a nuclear battery850 Polonium-210 in a nuclear battery57 000 Energy Content in Different Type of Batteries IT IS A STAGGERINGLY SMALL WORLD THAT IS BELOW,” Said physicist Richard P. Feynman in his visionary talk to the American Physical Society, when he envisioned the fabrication of micro- and nano devices and declared that one day the entire Encyclopaedia Britannica could be written on the head of a pin. Feynman’s vision has finally begun to manifest, thanks to ever more sophisticated microelectronics. Micro and nano scale machines are ushering a multibillion-dollar market as they are being incorporated in virtually every electronic devices.
Among the trendsetting applications in this development are ultra dense memories capable of storing hundreds of gigabytes in a fingernail-size device, micromirrors for enhanced display and optical communications equipment, and highly selective RF filters to reduce cell phones size and improve the quality of calls. But, again, at very small scales, chemical batteries can’t provide enough power for these micro machines. As the size of such a battery is reduced, the amount of stored energy goes down exponentially.
Reduction in each side of a cubic battery by a factor of 10 as the volume is reduced —and therefore the energy that can be stored— reduces by a factor of 1000. In fact, the sensors today which are no larger than a speck of dust require batteries which are as large as a shirt button!!!!! COMPARISION WITH OTHER WELL KNOWN ENERGY SOURCES FOR NANO DEVICES In a bid to power these nano devices, researchers are turning away from conventional fuels like hydrogen and hydrocarbons (propane, methane, gasoline and diesel) and are meddling with micro fuels that consume hydrogen to generate power like other conventional fuels.
Many are also developing on- board combustion engines that consume hydrogen to generate energy much like an average automobile. But these approaches are facing many hurdles. The primary road block is relatively low energy densities of these mechanisms and other being the continuous need to supply the fuel and eliminate the by-products formed . In case of other liquid fuels the major challenge is to develop a packaging that will contain sufficient liquid fuel to power these devices and which can be scaled down to micro and nano sizes at the same time.
The nuclear batteries that are being developed won’t require any refilling or recharging. and will last as long as the half-life of the radioactive source. And even though their efficiency in converting nuclear to electrical energy isn’t high—about 4 percent—the extremely high energy density of the radioactive materials makes it possible for these micro batteries to produce relatively significant amounts of power. For example, with 10 milligrams of polonium-210 (contained in about 1 cubic millimeter), a nuclear powered battery could produce 50 milliwatts of electric power for more than four months.
With that level of power, it would be possible to run a simple microprocessor and a handful of sensors for four continuous months. Specific Power Density Of Leading Power Isotopes KEY ELEMENTS OF THE TECHNOLOGY Why not conventional Gamma Emitters?? The first lesson to be learned here is: What are Radioisotopes?? Radioisotopes are basically unstable atoms that spontaneously emit high-energy particles as they decay to a more stable state. Most radioisotopes emit Gamma rays (which are essentially high-energy X-rays that can penetrate most materials including human flesh).
But radioisotopes used in nuclear battery emit Alpha particles (an aggregate of two protons and two neutrons) and Beta particles (high-energy electrons) that can’t penetrate as deeply and therefore pose less risk. Another reason why Gamma Emitters are not considered for development of the nuclear battery is that they would require sufficient amount of shielding. The Alpha Emitters, on the other hand, have an advantage due to the short range of the Alpha particles. This short range allows increased efficiency and thus provides more design flexibility, assuming that a sufficient activity can be achieved.
The half life of the isotopes must be high enough so that the useful life of the battery is sufficient for typical applications, and low enough to provide sufficient activity. In addition, the new isotope resulting after decay should be stable, or it should decay without emitting Gamma radiation. The nuclear powered batteries that are being developed contain1 to 10 millicuries of nickel-63 or tritium, whose beta particles have relatively low energy and can be blocked by a layer of 25 to 100 micrometers of plastic, metal, or semiconductor (they are even blocked by the thin dead-skin layer covering our bodies. ) ISOTOPERADIATION TYPEHALF LIFE Yr)MAX. ENERGY (keV)AVERAGE ENERGY H-3Beta12. 3 y18. 65. 7 Ni-63Beta100. 2 y66. 917. 4 Po-210Alpha138. 8 y530. 43- Commonly Used Isotopes NUCLEAR BATTERIES WHICH ARE CURRENTLY USED JUNCTION TYPE BATTERY This type of battery is very useful for long term applications in devices like space crafts,battle field sensors and nanoelectric sensors.. The device basically consists of a small quantity of Nickel-63 placed near an ordinary silicon p-n junction( hence the name)—a diode, basically. As the Nickel-63 decays it emits beta particles, which are high-energy electrons that spontaneously fly out of the radioisotope’s unstable nucleus.
The emitted beta particles ionizes the diode’s atoms, creating paired electrons and holes that diffuse away from each other at the p-n junction. These separated electrons and holes travel away from the junction, thereby producing the current. Why Ni-63 is used in Junction Battery? Nickel-63 is ideal for this application because its emitted beta particles travel a maximum of 21 ? m in silicon before disintegrating; if the particles had more energy, they would travel longer distances, thus escaping the battery. This battery has a capacity of producing about 3 nanowatts, using 0. millicurie of Nickel-63 , power which is more than sufficient for nano devices. LATEST DEVELOPMENTS CANTILEVER BATTERIES These new types of batteries generate more power than a typical junction battery. These devices operate like generators where the radioactive energy is first converted into mechanical energy and then into pulses of electrical energy. Even though these devices involve an intermediate phase,their efficiency remain unaffected- if anything they actually tap the kinetic energy of the emitted particles for conversion into mechanical energy and hence provide a more continous flow of energy than conventional junction battery.
Figure 5 Beta particles move from radioactive source and accumulate at Copper plate leading to electrostatic force of attraction Why Thin Film RadioIsotope is used in Cantilever Batteries? This device primarily uses a thin film of radioisotope. On top of this film, a small rectangular piece of silicon is cantilevered, its free end able to move up and down. As the electrons move away from the radioactive source, they travel through the air gap and hit the cantilever, charging it negatively. The source, which is positively charged, then attracts the cantilever, bending it down .
This mechanical energy is converted instantaneously into electrical energy. SELF RECIPROCATING SiN BATTERIES These batteries use low stress thin film of SiN. In this device a Wheatstone bridge is formed using four resistors. The purpose of using Wheatstone bridge is to measure the deflections. The output from a Wheatstone bridge is sent to an operational amplifier and the amplified signal is measured. A self-timed reciprocating movement is obtained between the film of radioisotope and the cantilever arm.
As compared to a conventional thin film cantilevers they offer better efficiency as the RF signal conversion from mechanical signal is more streamlined and compact. OPTOEELCTRONIC BATTERIES An optoelectronic nuclear battery has been developed by the researchers of Kurchatov Institute of Moscow. The Beta emitter would power an excimer mixture ( argon and xenon) which would produce light to excite a photocell. The primary advantage of this battery is that precision electrodes are not required and most electrons contribute to battery’s power output. NANONUCLEAR BATTERIES
Any with technology “nano” suffixed ushers in a debate. A generally accepted criterion for labelling nanotechnology given by Mihail C. Roco( Ph. D. , a National Science Foundation Chair on the Nanoscale Science Engineering and Technology Subcommittee (NSEC) of the National Science and Technology Committee (NSTC)) states “one dimension of about one to 100 nanometers, designed through a process that exhibits fundamental control over the physical and chemical attributes of molecular-scale structures, and the ability to combine to form larger structures. ”
These technologies for the nano- nuclear battery have same operational and structural micro nuclear battery except it’s done on a nano level. These batteries have better efficiencies as compared to micro-nuclear batteries and the path for the research of nuclear battery ends at such nano powered devices. CURRENT PLAYERS NASA GLENN RESEARCH CENTRE, CLEAVELAND The scientists at the Glenn Research Centre are working in collaboration with the researchers at RIT on a project to develop alpha voltaic batteries for miniature military devices for US Army with sensing and communication capabilities.
This project will be of three years duration and will focus on use of a radioisotope Americium, which is used in smoke detector, along with handful of semiconductor devices to convert alpha energy into usable electricity. The project will conclude with full manufacture of device and plans for commercial manufacture. ROCHESTER INSTITUTE OF TECHNOLOGY RESEARCH LABORATORY, NEWYORK A team of researchers at RIT led by Ryne Rafelle, Head of physics and Microsystems have obtained funds ranging around $1. 2 million dollars from DARPA (Defence Advanced Project Research Agency) to develop nuclear power supplies for military use.
The researchers are planning on using an innovative nanomaterial (quantum dots) to protect the semiconductor used inside the battery from radiation damage. This will make the battery not only safer but also increase its life to unprecedented levels. KUSHATOV INSTITUTE, MOSCOW The technology for Optoelectric nuclear batteries was developed by a team of researchers at Kuchatov Institute. In a revolutionary development, they used Radioisotope Strontium-90 and Technetium-99 as beta emitters suspended in gas or liquid which permits nearly lossless transmission of beta energy. PRIVATE PLAYERS (QYNERGY CORPORATION, ALPLA V INC. WIDETRONIX ETC. ) These are leading private players company harvesting nuclear energy for the purpose of providing cutting edge energy and power solution that are not provided by current battery and storage system. Using their proprietary technologies they have developed high density power cell using the energy generated by radioisotopes. ECONOMIC POTENTIAL SPACE APPLICATIONS- SATELLITE AND INTERSTELLAR PROBE Radio isotropic Thermoelectric Generator(RTGs) are nuclear batteries which consists of stacks of thermocouples which convert the thermal energy obtained from the decay of radioisotope into usable electrical energy.
They have emerged as the most popular power sources for the unmanned and unmaintained locations requiring power less than few hundred watts for durations which are too long for conventional fuel cells and where solar panels are not feasible. RTGs are used as power sources in the satellites, space probe vehicles by NASA and in various unmanned remote locations, like a series of lighthouses built by the USSR in the Arctic Circle. Systems for Nuclear Auxiliary Power (SNAP) units which comprise of handful of RTGs are used especially for probes that travel far enough from the Sun that solar panels are no longer viable.
Pioneer 10, Pioneer 11, Voyager 1, Galileo, Ulysses, Cassini and New Horizons used RTGs to meet their power requirements. Also, RTGs were used to power the two Viking landers and for the scientific experiments left on the Moon by the crews of Apollo 12. RTG also used on interstellar precursor missions and interstellar probes. One such example is the Innovative Interstellar Explorer (2003-current) proposal from NASA which will be using RTG Am-241 This could support mission extensions up to 1000 years. UNDERSEA APPLICATIONS- DEEP SEA SENSORS
The recent tsunami, earthquake and other under water phenomena have increased the demand for underwater sensors which can withstand such extreme conditions. These sensors are integrated with nuclear batteries which can work for longer durations in inaccessible places under crude situations. MEDICAL APPLICATIONS- NUCLEAR PACEMAKERS In early days, pacemakers used were powered with mercury and zinc batteries which could run for three years. Most often however, such mercury battery would fail in 20 months requiring the patient to undergo another implant for the replacement of the device.
Nuclear Batteries are used extensively in the pacing industry to prolong the longevity of the implanted device. Pacemakers, implanted with nuclear batteries, offer young patients the chance to go through their entire lifetime with just a single implant. MOBILE DEVICES- CELLPHONES & LAPTOPS Xcell-N is a nuclear powered laptop battery that provides between seven and eight thousand times battery life as compared to a normal laptop battery- thus any laptop can be kept on for five continous years without having to charge it.
Xcell- N is in continuous working state since the past eight months and neither has been turned off nor has been plugged into electrical power. Most cell phones use RF filters for frequency selection which occupy a large part of the volume. Researchers are currently developing MEMS based RF filters which provides not only better frequency selectivity (thus better quality of calls) but also reduced sizes. These MEMS filters, however, may require relatively high dc voltages, and drawing it from the main battery would require complicate electronics.
Instead, a nuclear powered battery designed to generate the required voltage—in the range of 10 to 100 volts—could be used to juice up the filter directly and more efficiently. AUTOMOBILES Although it is in initial stages of development but it is expected that nuclear powered batteries will soon replace the weary chemical batteries. This implies that running short of fuel or time will be things of past. Fox Valley Auto Electric Association has already started working on the ways to implement this. CHALLENGES
Though there are many merits the nuclear battery there are few challenges too, which needs to be overcome to make it realty, in the immediate future. SAFETY Since nuclear powered batteries involve the use of small amounts of radiation and radioactive materials, it is necessary that they must comply with current Radiation Protection Standards which are based on the Linear Non-Threshold model (LNT) . This model assumes that any amount of radiation exposure, no matter how small, will have a detrimental effect on health.
The external dose associated with the radioisotopes used in these batteries is zero, because an alpha particle needs to have an energy of more than 7. 5 MeV to penetrate the protective layer of the skin (0. 07 mm think), and a ? particle needs to have an energy of more than 70 keV. Since radio isotopes in nuclear batteries have energies lower than these they are unable to penetrate the skin. INHALATION INGESTION DOSE LIMIT [mrem/d]44. 575. 479 Dose Equivalent [mrem/d]No. of batteries to be inhaled to reach the limitDose Equivalent [mrem/d]No. of batteries to be swallowed to reach the limit H32. 418. 0346158 Ni645. 697. 081367
Radiation Levels After Ingestion or Inhalation Of 5µCi of Ni or H Nuclear Battery In fact, radioisotopes have been used for decades in commercial applications. Many smoke detectors contain 1 to 5 microcuries of Americium-241, used to ionize the air between a pair of parallel plates. And some emergency exit signs in public buildings, schools, and auditoriums that have to remain visible during power outages contain 8 to 10 curies of tritium, whose emitted electrons excite phosphor atoms, illuminating the sign. The amount of radioactive material in the nuclear batteries falls between that in a smoke detector and in an exit sign.
And for whatever amount, any commercial application of such nuclear powered batteries will have to comply with all the established safety measures (including design of safe packaging) and follow regulations about handling and disposing of the device. COST As it is the case with the most ground breaking technology , the initial cost of production is quite high. But as the product goes for mass production the cost goes down. The major challenge lies in finding sources of inexpensive radioisotopes that can be efficiently integrated into the electronic devices.
For example 1 millicurie of Ni-63 costs around $25. But the researchers have come up with a potentially cheaper alternative tritium which is produced by some nuclear reactors as a by product and costs few cents( for 1 millicurie). WASTE DISPOSAL The environmental impact of disposing of the nuclear devices once their useful life has ended, as well as the associated costs are minimal. Since after three half-lives the activity of the isotope decays to about 10% of the original activity, the nuclear powered batteries would be below background radiation level by that time. SOCIAL ACCEPTANCE
The nuclear technology has lost its credibility as the world has seen enough nuclear disasters. Thus acceptance for the nuclear technology will be very hard to come by. However the immense potential of this technology will soon overpower this initial resistance. CONCLUSION & WAY FORWARD Clearly the current state of research is making it harder to deny that chemical batteries will be replaced by nuclear powered batteries- and soon. Nuclear Batteries present a logical solution to the burgeoning need for a safe, reliable, compact, lightweight, longer lasting and self contained power supply.
They not only protect our declining natural resources but also serve to make our traditional energy sources redundant. As the energy associated with the radioactive materials is much more than the conventional sources and by far the highest without any waste generation, the world can be transformed into a new one without green houses gases and its associated risks. Scientists have overcome a major stumbling block to make mass production of these batteries a viable and hugely profitable option. The system we have developed is mechanically simple, potentially leading to more compact, more reliable and less expensive systems. This was an attempt at something that seemed viable. ", said Mark Prelas , Director of Research at University of Wisconsin’s Nuclear Science and Engineering Institute. Recent breakthroughs, at University of Missouri where the researchers have developed a economically feasible energy conversion system that uses safe isotopes to generate high-grade energy, only prove that these MEMS Marvels are going to be very successful in near future.
Success of few similar small projects will give sufficient learning to make this technology big very soon. REFERENCES 1. “Nuclear and Radiochemistry” , Gerhardt Friedlander and Joseph W. Kennedy 2. Technolyreview. com 3. Powerpaper. com 4. http://ieeexplore. ieee. org/stamp/stamp. jsp? arnumber=01330808 5. http://en. wikipedia. org/wiki/Atomic_battery 6. http://www. physorg. com/news174139641. html 7. http://www. scribd. com/doc/8929973/Nuclear-Battery
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