The Atomic Battery
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07-06-2009, 01:36 AM
The typical future-tech scenario calls for millions of low-powered radio frequency devices scattered throughout our environment -- from factory-floor sensor arrays to medical implants to smart devices for battlefields.
Because of the short and unpredictable lifespans of chemical batteries, however, regular replacements would be required to keep these devices humming. Fuel cells and solar cells require little maintenance, but the former are too expensive for such modest, low-power applications, and the latter need plenty of sun.
A third option, though, may provide a powerful -- and safe -- alternative. It's called the Direct Energy Conversion (DEC) Cell, a betavoltaics-based 'nuclear' battery that can run for over a decade on the electrons generated by the natural decay of the radioactive isotope tritium. It's developed by researchers at the University of Rochester and a startup, BetaBatt, in a project and implimentation described in the May 13 issue of Advanced Materials and funded in part by the National Science Foundation.
Because tritium's half-life is 12.3 years (the time in which half of its radioactive energy has been emitted), the DEC Cell could provide a decade's worth of power for many applications. Clearly, that would be an economic boon -- especially for applications in which the replacement of batteries is highly inconvenient, such as in medicine and oil and mining industries, which often place sensors in dangerous or hard-to-reach locations.
'One of our main markets is for remote, very difficult to replace sensors,' says Larry Gadeken, chief inventor and president of BetaBatt. 'You could place this [battery] once and leave it alone.'
Betavoltaic devices use radioisotopes that emit relatively harmless beta particles, rather than more dangerous gamma photons. They've actually been tested in labs for 50 years -- but they generate so little power that a larger commercial role for them has yet to be found. So far, tritium-powered betavoltaics, which require minimal shielding and are unable to penetrate human skin, have been used to light exit signs and glow-in-the-dark watches. A commercial version of the DEC Cell will likely not have enough juice to power a cell phone -- but plenty for a sensor or pacemaker.
The key to making the DEC Cell more viable is increasing the efficiency with which it creates power. In the past, betavoltaics researchers have used a design similar to a solar cell: a flat wafer is coated with a diode material that creates electric current when bombarded by emitted electrons. However, all but the electron particles that shoot down toward the diodes are lost in that design, says University of Rochester professor of electrical and computer engineering Phillipe Fauchet, who developed the more-efficient design based on Gadeken's concept.
The solution was to expose more of the reactive surface to the particles by creating a porous silicon diode wafer sprinkled with one-micron wide, 40 micron-deep pits. When the radioactive gas occupies these pits, it creates the maximum opportunity for harnessing the reaction.
As importantly, the process is easily reproducible and cheap, says Fauchet -- a necessity if the DEC Cell is to be commercially viable.
The fabrication techniques may be affordable, but the tritium itself -- a byproduct of nuclear power production -- is still more expensive than the lithium in your cell-phone battery. The cost is less of an issue, however, for devices designed specifically to collect hard-to-get data.
Cost is only one reason why Gadeken says he will not pursue the battery-hungry consumer electronics market. Other issues include the regulatory and marketing obstacles posed by powering mass-market devices with radioactive materials and the large battery size that would be required to generate sufficient power. Still, he says, the technology might some day be used as a trickle-recharging device for lithium-ion batteries.
Instead, his company is targeting market sectors that need long-term battery power and have a comfortable familiarity with nuclear materials.
'We're targeting applications such as medical technology, which are already using radioactivity,' says Gadeken.
For instance, many implant patients continue to outlive their batteries and require costly and risky replacement surgery.
Eventually, Gadeken hopes to serve NASA as well, if the company can find a way to extract enough energy from tritium to power a space-faring object. Space agencies are interested in safer and lighter power sources than the plutonium-powered Radioisotope Thermal Generators (RTG) used in robotic missions, such as Voyager, which has an RTG power source that is intended to run until around 2020.
Furthermore, a betavoltaics power source would likely alleviate environmental concerns, such as those voiced at the launch of the Cassini satellite mission to Saturn, when protestors feared that an explosion might lead to fallout over Florida.
For now, though, Gadeken hopes to interest the medical field and a variety of niche markets in sub-sea, sub-surface, and polar sensor applications, with a focus on the oil industry.
And the next step is to adapt the technology for use in very tiny batteries that could power micro-electro-mechanical Systems (MEMS) devices, such as those used in optical switches or the free-floating 'smart dust' sensors being developed by the military.
In fact, another betavoltaics device, under development at Cornell University, is also targeting the MEMS power market. The Radioisotope-Powered Piezoelectric Generator, due in prototype form in a few years, will combine a betavoltaics cell with a tritium-powered electromechanical cantilever device first demonstrated in 2002.
Amit Lal, one of the Cornell researchers, offers both praise and cautious skepticism about the DEC Cell. While he's impressed with the power output from the DEC Cell, he said that there are still issues with power leakage. To avoid those potential leakage problems, Cornell is using a slightly larger-scale wafer design. They're also planning to move to a porous design and either solid or liquid tritium to improve efficiency.
Lal also notes that the market for either Cornell's device or the DEC Cell might be squeezed by newer, longer-lasting lithium batteries. Still, there's a niche for very small devices, he believes, especially those that must run longer than ten years.
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A burgeoning need exists today for small, compact, reliable, lightweight and self-contained rugged power supplies to provide electrical power in such applications as electric automobiles, homes, industrial, agricultural, recreational, remote monitoring systems, spacecraft and deep-sea probes. Radar, advanced communication satellites and especially high technology weapon platforms will require much larger power source than today’s power systems can deliver. For the very high power applications, nuclear reactors appear to be the answer. However, for intermediate power range, 10 to 100 kilowatts (kW), the nuclear reactor presents formidable technical problems.
Because of the short and unpredictable lifespan of chemical batteries, however, regular replacements would be required to keep these devices humming. Also, enough chemical fuel to provide 100 kW for any significant period of time would be too heavy and bulky for practical use. Fuel cells and solar cells require little maintenance, and the latter need plenty of sun.
Thus the demand to exploit the radioactive energy has become inevitably high. Several methods have been developed for conversion of radioactive energy released during the decay of natural radioactive elements into electrical energy. A grapefruit-sized radioisotope thermo- electric generator that utilized heat produced from alpha particles emitted as plutonium-238 decay was developed during the early 1950’s.
Since then the nuclear has taken a significant consideration in the energy source of future. Also, with the advancement of the technology the requirement for the lasting energy sources has been increased to a great extent. The solution to the long term energy source is, of course, the nuclear batteries with a life span measured in decades and has the potential to be nearly 200 times more efficient than the currently used ordinary batteries. These incredibly long-lasting batteries are still in the theoretical and developmental stage of existence, but they promise to provide clean, safe, almost endless energy.
Unlike conventional nuclear power generating devices, these power cells do not rely on a nuclear reaction or chemical process do not produce radioactive waste products. The nuclear battery technology is geared towards applications where power is needed in inaccessible places or under extreme conditions.
The researchers envision its uses in pacemakers and other medical devices that would otherwise require surgery to repair or replace. Additionally, deep-space probes and deep-sea sensors, which are beyond the reach of repair, would benefit from such technology. In the near future this technology is said to make its way into commonly used day to day products like mobile and laptops and even the smallest of the devices used at home. Surely these are the batteries of the near future.
The idea of nuclear battery was introduced in the beginning of 1950, and was patented on March 3rd, 1959 to tracer lab. Even though the idea was given more than 30 years before, no significant progress was made on the subject because the yield was very less.
A radio isotope electric power system developed by inventor Paul Brown was a scientific break through in nuclear power. Brown’s first prototype power cell produced 100,000 times as much energy per gram of strontium -90(the energy source) than the most powerful thermal battery yet in existence. The magnetic energy emitted by the alpha and beta particles inherent in nuclear material. Alpha and beta particles are produced by the radio active decay of certain naturally occurring and man –made nuclear material (radio nuclides). The electric charges of the alpha and beta particles have been captured and converted to electricity for existing nuclear batteries, but the amount of power generated from such batteries has been very small.
Alpha and beta particles also posses kinetic energy, by successive collisions of the particles with air molecules or other molecules. The bulk of the R &D of nuclear batteries in the past has been concerned with this heat energy which is readily observable and measurable. The magnetic energy given off by alpha and beta particles is several orders of magnitude grater than the kinetic energy or the direct electric energy produced by these same particles. However, the myriads of tiny magnetic fields existing at any time cannot be individually recognized or measured. This energy is not captured locally in nature to produce heat or mechanical effects, but instead the energy escapes undetected.
Brown invented an approach to “organize” these magnetic fields so that the great amounts of otherwise unobservable energy could be harnessed. The first cell constructed (that melted the wire components) employed the most powerful source known, radium-226, as the energy source.
The main draw back of Mr. Brown’s prototype was its low efficiency, and the reason for that was when the radioactive material decays, many of the electrons lost from the semiconductor material. With the enhancement of more regular pitting and introduction better fuels the nuclear batteries are though to be the next generation batteries and there is hardly any doubt that these batteries will be available in stores within another decade.
ENERGY PRODUCTION MECHANISM
Betavoltacis is an alternative energy technology that promises vastly extended battery life and power density over current technologies. Betavoltaics are generators of electrical current, ineffect a form of a battery, which use energy from a radioactive source emitting beta particles (electrons). The functioning of a betavoltaics device is somewhat similar to a solar panel, which converts photons (light) into electric current.
Betavoltaic technique uses a silicon wafer to capture electrons emitted by a radioactive gas, such as tritium. It is similar to the mechanics of converting sunlight into electricity in a solar panel. The flat silicon wafer is coated with a diode material to create a potential barrier. The radition absorbed in the vicinity of and potiential barrier like a p-n junction or a metal-semiconductor contact would generate separate electron-hole pairs which inturn flow in an electric circuit due to the voltaic effect. Of course, this occurs to a varying degree in different materials and geometries.
A pictorial representation of a basic Betavoltaic conversion as shown in figure 1. Electrode A (P-region) has a positive potential while electrode B (N-region) is negative with the potential difference provided by me conventional means.
The junction between the two electrodes is comprised of a suitably ionisable medium exposed to decay particles emitted from a radioactive source.
The energy conversion mechanism for this arrangement involves energy flow in different stages:
Stage 1:- Before the radioactive source is introduced, a difference in potential between to electrodes is provided by a conventional means. An electric load RL is connected across the electrodes A and B. Although a potential difference exists, no current flows through the load RL because the electrical forces are in equilibrium and no energy comes out of the system. We shall call this ground state E0.
Stage 2:- Next, we introduce the radioactive source, say a beta emitter, to the system. Now, the energy of the beta particle Eb generates electron- hole pair in the junction by imparting kinetic energy which knocks electrons out of the neutral atoms. This amount of energy E1, is known as the ionization potential of the junction.
Stage 3:- Further the beta particle imparts an amount of energy in excess of ionization potential. This additional energy raises the electron energy to an elevated level E2. Of course the beta [particle dose not impart its energy to a single ion pair, but a single beta particle will generate as many as thousands of electron- hole pairs. The total number of ions per unit volume of the junction is dependent upon the junction material.
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11-02-2012, 08:47 PM
hello , im final year mechanical student ... i thought to do seminar and presentation on atomic battery, so plz can u send me it's report to email address firstname.lastname@example.org
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13-02-2012, 12:34 PM
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