02-03-2013, 10:14 AM
NUCLEAR BATTERIES
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ABSTRACT :
A radioisotope electric power system developed by inventor Paul Brown is a scientific breakthrough in nuclear power. The battery utilizes the energy given off by decaying radioactive
material, converting it directly into a continuous AC electrical current. Unlike conventional nuclear generating devices, the power cell does not rely on a nuclear reaction or chemical process and doesnot produce radioactive waste products.
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 nuclear battery yet in existence. The Nucell battery yielded 7500 watts per gram of strontium-90. Compare this to an advanced device recently developed by the US Dept. of Energy Byproducts Utilization Program. Their state-of-the-art thermal nuclear battery produced 0.063 watts per gram of strontium-90.
The key to the Nucell battery is Brown's discovery of a method to harness the magnetic energy given off by the alpha and beta particles inherent in nuclear material. Alpha and beta particles are produced by the radioactive decay of certain naturally occurring and man-made nuclear material (radionuclides).
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 possess 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.
INTRODUCTION
Micro electro mechanical systems (MEMS) comprise a rapidly expanding research field with potential applications varying from sensors in air bags, wrist-warn GPS receivers, and matchbox size digital cameras to more recent optical applications. Depending on the application, these devices often require an on board power source for remote operation, especially in cases requiring for an extended period of time. In the quest to boost micro scale power generation several groups have turn their efforts to well known enable sources, namely hydrogen and hydrocarbon fuels such as propane, methane, gasoline and diesel.
Some groups are developing micro fuel cells than, like their micro scale counter parts, consume hydrogen to produce electricity. Others are developing on-chip combustion engines, which actually burn a fuel like gasoline to drive a minuscule electric generator. But all these approaches have some difficulties regarding low energy densities, elimination of by products, down scaling and recharging. All these difficulties can be overcome up to a large extend by the use of nuclear micro batteries.
Radioisotope thermo electric generators (RTGs) exploited the extraordinary potential of radioactive materials for generating electricity. RTGs are particularly used for generating electricity in space missions. It uses a process known as See-beck effect. The problem with RTGs is that RTGs don't scale down well. 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.
DESCRIPTION OF NUCLEAR BATTERIES :
Nuclear batteries use the incredible amount of energy released naturally by tiny bits of radio active material without any fission or fusion taking place inside the battery. These devices use thin radioactive films that pack in energy at densities thousands of times greater than those of lithium-ion batteries. Because of the high energy density nuclear batteries are extremely small in size. Considering the small size and shape of the battery the scientists who developed that battery fancifully call it as "DAINTIEST DYNAMO". The word 'dainty' means pretty.
WORKING OF NUCLEAR BATTERIES :
As the Ni-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 ionized the diode's atoms, exciting unpaired electrons and holes that are separated at the vicinity of the p-n interface. These separated electrons and holes streamed away form the junction, producing current.
It has been found that beta particles with energies below 250KeV do not cause substantial damage in Si. The maximum and average energies (66.9KeV and 17.4KeV respectively) of the beta particles emitted by Ni-63 are well below the threshold energy, where damage is observing silicon. The long half-life period (100 years) makes Ni-63 very attractive for remote long life applications such as power of spacecraft instrumentation. In addition, the emitted beta particles of Ni-63 travel a maximum of 21 micrometer in silicon before disintegrating. If the particles were more energetic they would travel longer distances, thus escaping. These entire things make Ni-63 ideally suitable in nuclear batteries.
First the beta particles, which are high-energy electrons, fly spontaneously from the radioactive source. These electrons get collected on the copper sheet. Copper sheet becomes negatively charged. Thus an electrostatic force of attraction is established between the silicon cantilever and radioactive source. Due to this force the cantilever bends down.
The piece of piezoelectric material bonded to the top of the silicon cantilever bends along with it. The mechanical stresses of the bend unbalances the charge distribution inside the piezoelectric crystal structure, producing a voltage in electrodes attached to the top and bottom of the crystal.
Direct Charging Generators :
In this type, the primary generator consists of a high –Q LC tank circuit. The energy imparted to radioactive decay products during the spontaneous disintegrations of radioactive material is utilized to sustain and amplify the oscillations in the high-Q LC tank circuit 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 mixture of three radioactive materials which decay primarily by alpha emission and provides a greater flux of radioactive decay products than the equivalent amount of single radioactive nuclei.
FUEL CONSIDERATIONS
The major criterions considered in the selection of fuels are:
• Avoidance of gamma in the decay chain
• Half life
• Particle range
• Watch out for (alpha, n) reactions
Any radioisotope in the form of a solid that gives off alpha or beta particles can be utilized in the nuclear battery. The first cell constructed (that melted the wire components) employed the most powerful source known, radium-226, as the energy source. However, radium-226 gives rise through decay to the daughter product bismuth-214, which gives off strong gamma radiation that requires shielding for safety. This adds a weight penalty in mobile applications.
Radium-226 is a naturally occurring isotope which is formed very slowly by the decay of uranium-238. Radium-226 in equilibrium is present at about 1 gram per 3 million grams of uranium in the earths crust. Uranium mill wastes are readily available source of radium-226 in very abundant quantities. Uranium mill wastes contain far more energy in the radium-226 than is represented by the fission energy derived form the produced uranium.
Strontium-90 gives off no gamma radiation so it does not necessitate the use of thick lead shielding for safety.strrrontium-90 does not exist in nature, but it is one of the several radioactive waste products resulting from nuclear fission. The utilizable energy from strontium-90 substantially exceeds the energy derived from the nuclear fission which gave rise to this isotope.
Once the present stores of nuclear wastes have been mined, the future supplies of strontium-90 will depend on the amount of nuclear electricity generated hence strontium-90 decay may ultimately become a premium fuel for such special uses as for perpetually powered wheel chairs and portable computers. Plutonium-238 dioxide is used for space application. Half life of tantalum-180m is about 1015 years. In its ground state, tantalum-180 (180Ta) is very unstable and decays to other nuclei in about 8 hours but its isomeric state, 180m Ta, is found in natural samples. Tantalum 180m hence can be used for switchable nuclear batteries.
CONCLUSION :
The world of tomorrow that science fiction dreams of and technology manifests might be a very small one. It would reason that small devices would need small batteries to power them. The use of power as heat and electricity from radioisotope will continue to be indispensible. As the technology grows, the need for more power and more heat will undoubtedly grow along with it.
Clearly the current research of nuclear batteries shows promise in future applications for sure. With implementation of this new technology credibility and feasibility of the device will be heightened. The principal concern of nuclear batteries comes from the fact that it involves the use of radioactive materials. This means through out the process of making a nuclear battery to final disposal, all radiation protection standards must be met. The economic feasibility of the nuclear batteries will be determined by its applications and advantages. With several features being added to this little wonder and other parallel laboratory works going on, nuclear cells are going to be the next best thing ever invented in the human history.