1 A Seminar Report On NUCLEAR MICRO - BATTERY Submitted by UTKARSH KUMAR in partial fulfilment for Bachelor of Technology (B. Tech) In ELECTRONICS & INSTRUMENTATION ENGINEERING DEPARTMENT OF ELECTRONICS & INSTRUMENTATION AJAY KUMAR GARG ENGINEERING COLLEGE GHAZIABAD-201009
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This is to certify that the seminar report entitled
NUCLEAR MICRO-BATTERY
is a bonafide record of the work done by MR. UTKARSH KUMAR,ROLL NO. 1302732037 our supervision in partial fulfilment of the requirements for Bachelor of Technology in electronics and instrumentation from Ajay Kumar Garg Engineering college, Ghaziabad, for the year 2015-16.
SUBMITTED TO : SUBMITTED BY :
MR. NARESH KUMAR UTKARSH KUMAR
Dept. of electronics & Instrumentation
Seminar Co-coordinator
JANUARY 2016
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ACKNOWLEDGEMENT
It is matter of great pleasure for me to submit this seminar report on “NUCLEAR
MICRO-BATTERY”, as a part of curriculum forward of “Bachelor of
Technology with specialization in Electronics & Instrumentation” Department Of
E&I , AKGEC.
I am extremely thankful to Prof. P K Chopra, Head Of Department, Department of Eletronics & Instrumentation, AKGEC for permitting me to undertake this work.
I express my heartfelt gratitude to my respected Seminar guide Mr. Naresh Kumar for his kind and inspiring advice which helped me to understand the subject and its semantic significance. He enriched me with valuable suggestions regarding my topic and presentation issues. I am also very thankful to my colleagues who helped and co-operated with me in conducting the seminar by their active participation.
Last but not least, I am thankful to my parents, who have encouraged & inspired me in every possible way.
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ABSTRACTMicroelectromechanical Systems (MEMS) have not gained wide use because they lack the on-device power required by many important applications. Several forms of energy could be considered to supply this needed power (solar, fossil fuels, etc), but nuclear sources provide an intriguing option in terms of power density and lifetime. This report describes several approaches for establishing the viability of nuclear sources for powering realistic MEMS devices. Isotopes currently being used include low-energy beta emitters (solid and liquid) and alpha emitters (solid). Several approaches are being explored for the production of MEMS power sources. The first concept is a junction-type battery. In this case, the charged particles emitted from the decay of the radioisotopes are absorbed by a semiconductor and dissipate most of their energy as ionization of the atoms in the solid. The carriers generated in this fashion are in excess of the number permitted by thermodynamic equilibrium and, if they diffuse to the vicinity of a rectifying junction, induce a voltage across the junction. The second concept involves a more direct use of the charged particles produced by the decay: the creation of a resonator by inducing movement due to attraction or repulsion resulting from the collection of charged particles. As the charge is collected, the deflection of a cantilever beam increases until it contacts a grounded element, thus discharging the beam and causing it to return to its original position. This process will repeat as long as the source is active. One final concept relies on temperature gradients produced by the sources, along with appropriate insulation, to create power using a Peltier device. The source is isolated in order to allow it to reach sufficient temperatures, and the temperature difference between the source and the rest of the device is exploited using the Peltier effect. Performance results will be provided for each of these concepts.
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Table of ContentsChapter Page no.
1.Introduction 6
2.MEMS 7
3.Historical Developments 10
4.Energy Production Mechanism 11
5.Junction type nuclear battery 14
6.Self-reciprocating cantilever 17
7.Isotope selection 21
8. Incorporation Of Source Into Device 22
9.Safety assessment 23
10.Advantages 24
11.Disadvantages 25
12.Applications 26
13.Conclusion 27
14.Reference 28
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INTRODUCTIONA 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.
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Microelectromechanical systems (MEMS):
Microelectromechanical system is the technology of very small devices. It merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology.
In general it can be defined as miniaturized mechanical and electro-mechanical elements (i.e., devices and structures) that are made using the techniques of microfabrication. The critical physical dimensions of MEMS devices can vary from well below one micron on the lower end of the dimensional spectrum, all the way to several millimeters. MEMS technology is based on a number of tools and methodologies, which are used to form small structures with dimensions in the micrometer scale (one millionth of a meter). Significant parts of the technology have been adopted from integrated circuit (IC) technology. For instance, almost all devices are built on wafers of silicon, like ICs. The structures are realized in thin films of materials, like ICs. They are patterned using photolithographic methods, like ICs.
While the functional elements of MEMS are miniaturized structures, sensors, actuators, and microelectronics, the most notable (and perhaps most interesting) elements are the micro sensors and micro actuators. Micro sensors and micro actuators are appropriately categorized as “transducers”, which are defined as devices that convert energy from one form to another. In the case of micro sensors, the device typically converts a measured mechanical signal into an electrical signal.
One of the basic building blocks in MEMS processing is the ability to deposit thin films of material with a thickness anywhere between a few nanometres to about 100 micrometres. There are two types of deposition processes, as follows:
Physical deposition-
Physical vapor deposition ("PVD") consists of a process in which a material is removed from a target, and deposited on a surface. Techniques to do this include the process of sputtering, in which an ion beam liberates atoms from a target, allowing them to move through the intervening space and deposit on the desired substrate, and evaporation, in which a material is evaporated from a target using either heat (thermal evaporation) or an electron beam (e-beam evaporation) in a vacuum system.
Chemical deposition-
Chemical deposition techniques include chemical vapor deposition ("CVD"), in which a stream of source gas reacts on the substrate to grow the material desired. Oxide films can also be grown by the technique of thermal oxidation, in which the (typically silicon) wafer is exposed to oxygen and/or steam, to grow a thin surface layer of silicon dioxide.
Patterning:
Patterning in MEMS is the transfer of a pattern into a material.
Lithography-
Lithography in MEMS context is typically the transfer of a pattern into a photosensitive material by selective exposure to a radiation source such as light. A photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source. If a photosensitive material is selectively exposed to radiation (e.g. by masking some of the radiation) the pattern of the radiation on the material is transferred to the material exposed, as the properties of the exposed and unexposed regions differs.
Diamond patterning-.
Diamond patterning is a method of forming diamond MEMS.
Etching processes
There are two basic categories of etching processes: wet etching and dry etching. In the former, the material is dissolved when immersed in a chemical solution. In the latter, the material is
sputtered or dissolved using reactive ions or a vapor phase etchant.[9][10] for a somewhat dated overview of MEMS etching technologies.
Dye preparation:
After preparing a large number of MEMS devices on a silicon wafer, individual dies have to be separated, which is called die preparation in semiconductor technology. For some applications, the separation is preceded by wafer back grinding in order to reduce the wafer thickness.
In order to understand the behavior of the system we have developed an analytical model for
both the charge collection and deflection of the cantilever. The charge collecting process is
governed by:
dQ=αdt−VR
dt
where dQ is the amount of charge collected by the beam during a given time dt, α represents the
current emitted by the radioactive source, V is the voltage across the source and the beam and R
is the effective resistance between them. The second term on the right hand side represents the
current leakage arising from the ionization of the air. Since V = Q / C, where C is the capacitance
of the beam and the source, the previous equation can be rearranged to obtain:
dQdt
+ 1RC
Q=α
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Figure 6 shows a typical experimental result, in which the initial distance is 3.5 mm and the
vacuum is 50 mTorr.
Figure 6: Deflection vs. time at a pressure of 50 mTorr
This equation can be readily solved:
Q=αRC ¿)
In Figure 6 we observe that the beam bends very slowly. Therefore, the electrostatic force on the beam can be taken as balanced by the elastic force from the beam itself. Since the electrostatic force is proportional to Q2 and the distance between the beam and the source can be taken as a constant, being δ the deflection of the beam, we have:
kδ∝α 2 R2 C2(1−e−t /RC)2
K is the elastic constant of the beam, α can be assumed to be constant since 63Ni has a half life of more than 100 years, R in the experiment is also a constant because the pressure is maintained and no breakdown of the air happened, otherwise the beam will bounce back. C can also be assumed to be constant because it has been observed experimentally that the deflection of the beam is very small compared to the initial distance between the beam and the radioactive source. Therefore:
α∝(1−e−t /RC)2
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Figure 7 compares the deflection measured experimentally with the values obtained analytically
according to the discussion shown above, by fitting R. We observe a very good match between
them.
Figure 7: Comparison between the experimental and analytical values for the deflection.
This model, however, does not include the periodic behavior of this device. Current experiments
show a minimum period of about 30 minutes, at which time the electrostatic energy is released as
electric current. Further studies are being done in this area, trying to identify the key
characteristics of the system in order to be able to design the device with the period and energy
release level appropriate for each particular application.
ISOTOPE SELECTION
A critical aspect of the creation of microbatteries for MEMS devices is the choice of the isotope to be used as a power source. Some requirements for this isotope include safety, reliability, cost, and activity. Since the size of the device is an issue in this particular application, gamma emitters have not been considered because they would require a substantial amount of shielding. Both pure alpha and low energy beta emitters have been used. The alpha emitters 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 halflife 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 isotopes currently in use for this work are:
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Table 1: Isotopes used for this work.
To explore the viability of the nuclear microbattery concept, some scoping calculations need to
be carried out. Using 210Po as an example, one can analyze the best case scenario, assuming
that the nuclear battery is created using pure 210Po. In this case, the activity would be
approximately 4,500 Ci per gram or 43,000 Ci per cubic centimeter. Thus, for a characteristic
source volume of 10-5 cubic centimeters (0.1 cm x 0.1cm x 10 microns), one obtains
approximately 0.5 Ci. Based on the results of previous experimental studies, the available power
would be on the order of 0.5 mW (about 1 mW/Ci). The power required for MEMS devices can
range from nanowatts to microwatts. A typical case is that of a low power CMOS driven
mechanical cantilever forming an air-gap capacitor with the substrate. Typical MEMS capacitors
have 10 femtoFarad capacitance and resonant frequencies of 10s of kHz. The power dissipated
for charging such an electromechanical capacitor would be in the range of 10 to 100 nanowatts.
Therefore, a pure source provides more than sufficient activity to power a practical device.
INCORPORATION OF SOURCES INTO THE DEVICE
Three methods of incorporating radioactive material into the MEMS devices are being studied. These are 1) activation of layers within the MEMS device, 2) addition of liquid radioactive material into fabricated devices, and 3) addition of solid radioactive material into fabricated devices. In the first approach, the parent material for the radioactive daughter or granddaughter would be manufactured as part of the MEMS device, most likely near the surface of the device. After fabrication of the device, the parent material would be exposed to the radiation field in our TRIGAreactor for a period of time until the desired radiation source strength is achieved. Highly absorbing neutron or charged particle materials would be used to mask other components of the device which are to remain non-radioactive. In addition, the material used for the activation would be chosen such that it has a high activation cross-section, thus maximizing the activation of the “source” and minimizing competing activity produced in surrounding structures. In the second and third approaches, radioactive sources are introduced into the MEMS device after fabrication. In the case of a liquid source, a reservoir must be created within the device, along with a channel providing access to the reservoir. The reservoir can then be filled, relying on capillary action to create the flow, and the channel can then be sealed off if needed. In the case of
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a solid source, the radioactive material will have to be deposited in selected sites on the device. We currently have two approaches to create this type of sources:
Electroless plating is the plating of nickel without the use of electrodes but by chemical reduction [1]. Metallic nickel is produced by the chemical reduction of nickel solutions with hypophosphite using an autocatalytic bath. The plating metal can be deposited in the pure form on to the plated surfaces. The bath is an aqueous solution of nickel salt and contains relatively low concentration of hypophosphite. This type of nickel plating can be used on a large group of metals, such as steel, iron, platinum, silver, nickel, gold, copper, cobalt, palladium and aluminum. Throughout the plating process, the bath needs to be heated to maintain it at a temperature in the range of 90 – 100 °C to promote the chemical reduction reaction. The boiling temperature ofthe bath is to be avoided. At lower temperatures the reaction proceeds slowly and at higher temperatures the bath evaporates. The important factor influencing the plating process is the pH. The pH needs to be maintained at 4.5-6 for plating to occur. A lower pH results in no plating at all. We have successfully plated gold-coated silicon pieces of dimensions 2mm by 2mm, following this procedure. Plating of nickel on gold was observed in about 15 minutes. These solid sources can then be incorporated into a MEMS device.
We have obtained glass microspheres (25 to 53 μm in diameter) that will emit low energy 3H beta radiation. These are obtained by irradiating 6Li glass silicate non-radioactive microspheres in the UW Nuclear Reactor. Using this procedure, we can produce activities of up to 12.8 mCi per gram and per hour of irradiation. Then, these
radioactive microspheres can be introduced in the MEMS device in the appropriate cavity. These latter approaches will allow for higher power densities than the direct reactor activation approach, but will provide less flexibility with respect to device design. We are currently exploring the tradeoffs of the different options, and will shortly release all the data needed to assess the viability of all of these approaches.
Waste DisposalOur analysis proves that the environmental impact of disposing of these micro-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 has decayed to about 10% of the original activity, the micro-batteries would be below background radiation level at the following times:
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SAFETY ASSESSMENT
Since this work involves the use of small amounts of radiation and radioactive materials, it is necessary to comply with current Radiation Protection Standards [2][3]. The potential health and environmental effects of fabricating, using and disposing of these nuclear micro-batteries have been studied in detail. Current radiation protection regulations are based on the Linear Non-Threshold model (LNT), which assumes that any amount of radiation exposure, no matter how small, may have negative health effects. This model was derived by extrapolating known acute (high dose and high dose rate) exposure data points in a linear or curvilinear fashion through the origin. Lately, however, there has been a movement among the Medical and Health Physics communities encouraging the review of the current regulations by using the Non-Linear Threshold model (NLT), that establishes that there are no detectable harmful health effects to humans at radiation levels below 100 mSv (10 rem). Therefore, even though we will prove that our devices do comply with current regulations, the actual health effects may be even more insignificant.
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ADVANTAGES
The most important feat of nuclear cells is the life span they offer, a minimum of 10years!
This is whopping when considered that it provides nonstop electric energy for the seconds
spanning these 10long years, which may simply mean that we keep our laptop or any hand held
devices switched-on for 10 years nonstop. Contrary to fears associated with conventional
batteries nuclear cells offers reliable electricity, without any drop in the yield or potential during
its entire operational period. Thus the longevity and reliability coupled together would suffice the
small factored energy needs for at least a couple of decades.
The largest concern of nuclear batteries comes from the fact that it involves the use of
radioactive materials. This means throughout the process of making a nuclear battery to final
disposal, all radiation protection standards must be met. Balancing the safety measures such as
shielding and regulation while still keeping the size and power advantages will determine the
economic feasibility of nuclear batteries. Safeties with respect to the containers are also
adequately taken care as the battery cases are hermetically sealed. Thus the risk of safety hazards
involving radioactive material stands reduced.
As the energy associated with fissile material is several times higher than conventional
sources, the cells are comparatively much lighter and thus facilitates high energy densities to be
achieved. Similarly, the efficiency of such cells is much higher simply because radioactive
materials in little waste generation. Thus substituting the future energy needs with nuclear cells
and replacing the already existing ones with these, the world can be seen transformed by
reducing the green house effects and associated risks. This should come as a handy savior for
almost all developed and developing nations. Moreover the nuclear produced therein are
substances that don’t occur naturally. For example strontium does not exist in nature but it is one
of the several radioactive waste products resulting from nuclear fission.
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DISADVANTAGES
First and foremost, as is the case with most breathtaking technologies, the high initial
cost of production involved is a drawback but as the product goes operational and gets into bulk
production, the price is sure to drop. The size of nuclear batteries for certain specific applications
may cause problems, but can be done away with as time goes by. For example, size of Xcell used
for laptop battery is much more than the conventional battery used in the laptops.
Though radioactive materials sport high efficiency, the conversion methodologies used
presently are not much of any wonder and at the best matches’ conventional energy sources.
However, laboratory results have yielded much higher efficiencies, but are yet to be released into
the alpha stage.
A minor blow may come in the way of existing regional and country specific laws
regarding the use and disposal of radioactive materials. As these are not unique worldwide and
are subject to political horrors and ideology prevalent in the country. The introduction legally
requires these to be scrapped or amended. It can be however be hoped that, given the
revolutionary importance of this substance, things would come in favor gradually.
Above all, to gain social acceptance, a new technology must be beneficial and
demonstrate enough trouble free operation that people begin to see it as a “normal” phenomenon.
Nuclear energy began to loose this status following a series of major accidents in its formative
years. Acceptance accorded to nuclear power should be trust-based rather than technology based.
In other words acceptance might be related to public trust of the organizations and individuals
utilizing the technology as opposed to based on understanding of the available evidence
regarding the technology.
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APPLICATIONS
Nuclear batteries find many fold applications due to its long life time and improved reliability. In the ensuing era, the replacing of conventional chemical batteries will be of enormous advantages. This innovative technology will surely bring break-through in the current technology which was muddled up in the power limitations. MEMS devices, with their integrated nuclear micro-battery will be used in large variety of applications, as sensors, actuators, resonators, etc. It will be ensured that their use does not resultin any unsafe exposure to radiation.
Space applications
In space applications, nuclear power units offer advantages over solar cells, fuel cells
and ordinary batteries because of the following circumstances:
1. When the satellite orbits pass through radiation belts such as the van-Allen belts
around the Earth that could destroy the solar cells
2. Space missions in the opaque atmospheres such as Jupiter, where solar cells
would be useless because of lack of light.
3. Operations on the Moon or Mars where long periods of darkness require heavy
batteries to supply power when solar cells would not have access to sunlight.
4. Heating the electronics and storage batteries in the deep cold of space at minus
245° F is a necessity.
5. At a distance far from the sun for long duration missions where fuel cells,
batteries and solar arrays would be too large and heavy.
So in the future it is ensured that these nuclear batteries will replace all the existing power
supplies due to its incredible advantages over the other. The applications which require a high
power, a high life time, a compact design over the density, an atmospheric conditions-
independent it is quite a sure shot that future will be of ‘Nuclear Batteries’. NASA is on the hot
pursuit of harnessing this technology in space applications.
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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 indispensable. 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 throughout 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.