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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

JANUARY 2016

P.O. Adhyatmik Nagar Adhyatmik Nagar, Hapur Bypass Rd, Bulandshahr Road

Industrial Area, Ghaziabad, Uttar Pradesh 201009

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CERTIFICATE

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.

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MEMS basic processes

Deposition processes

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

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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.

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HISTORICAL DEVELOPMENTS

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

breakthrough 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 radioactive 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 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 greater 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 drawback 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 nu0clear

batteries are thought to be the next generation batteries.

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ENERGY PRODUCTION MECHANISM

Betavoltaics

Betavoltaics is an alternative energy technology that promises vastly extended battery

life and power density over current technologies. Betavoltaics are generators of electrical current,

in effect 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

radiation absorbed in the vicinity of and potential barrier like a p-n junction or a metal-

semiconductor contact would generate separate electron-hole pairs which in turn 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 conventional means.

Figure 1

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.

in equilibrium and no energy comes out of the system. We shall call this ground state E0. stages:

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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

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.

Stage 4:- next, the electric field present in the junction acts on the ions and drives the electrons

into electrode A. the electrons collected in electrode A together with the electron deficiency of

electrode B establishes Fermi voltage between the electrodes. Naturally, the electrons in

electrode A seek to give up their energy and go back to their ground state (law of entropy).

Stage 5:- the Fermi voltage derives electrons from the electrode A through the load where they

give up their energy in accordance with conventional electrical theory. A voltage drop occurs

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across the load as the electrons give an amount of energy E3. Then the amount of energy

available to be removed from the system is

E3= Eb - E1 – L1-L2

Where L1 is the converter loss and L2 is the loss in the electrical circuit.

Stage 6:- the electrons, after passing to the load have an amount of energy E4.from the load, the

electrons are then driven into the electrode B where it is allowed to recombine with a junction

ion, releasing the recombination energy E4 in the form of heat this completes the circuit and the

electron has returned to its original ground state.

The end result is that the radioactive source acts as a constant current generator. Then the

energy balance equation can be written as

E0=Eb –E1 –E3-L1-L2

Diagram of micro machined pn junction

Until now betavoltaics has been unable to match solar-cell efficiency. The reason is

simple: when the gas decays, its electrons shoot out in all directions. Many of them are lost. A

new Betavoltaic device using porous silicone diodes was proposed to increase their efficiency.

The flat silicon surface, where the electrons are captured and converted to a current, and turned

into a 3- dimensional surface by adding deep pits. Each pit is about 1 micron wide. That is four

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hundred-thousandths of an inch. They are more than 40 microns deep. When the radioactive gas

occupies these pits, it creates the maximum opportunity for harnessing the reaction.

JUNCTION TYPE NUCLEAR BATTERY:

The electron-voltaic effects were studied extensively in the 1950’s and it was found that beta

particles with energies below 250 keV do not cause substantial damage in silicon [4][5].

Therefore, liquid 63Ni was selected as the radioactive source for these tests, since its maximum

and average energies (66.9 keV and 17.4 keV respectively) are well below the threshold energy

where damage is observed in silicon. In addition, its long half-life (100 year) makes it very

attractive for remote long-life applications, such as power of spacecraft instrumentation.

Figure 1: Diagram of a micromachined pn-junction

Since it is not easy to microfabricate solid radioactive materials (etching and cutting), a liquid

source is used instead for our micromachined pn-junction battery. As shown in Figure 1, a

number of bulk-etched channels have been micromachined in our pn-junction. Compared with

conventional planar pn-junctions, the three dimensional structure of our device allows for a

substantial increase of the junction area, and the micromachined channels can be used to store

the liquid source. Our pn-junction has 13 micromachined channels and the total junction area is

15.894 mm2 (about 55.82% more than the planar pn-junction). This can be very important since

the current generated by the powered pn-junction, whether it is powered by light or by a nuclear

source, is proportional to the junction area. Figure 2 shows the I-V curve of our pn-junction due

only to the interaction of light, as measured by a semiconductor parameter analyzer.

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Figure 3. I-V curve of a micromachined pn-junction powered by the light.

In order to measure the performance of our three-dimensional pn-junction in the presence of a

radioactive source, we use a pipette to place 8 µl of liquid 63Ni source (64 µCi) inside the

channels micromachined on top of the pn-junction, and then we cover it with a black box to

shield it from the light. The electric circuit used for these experiments is shown in Figure 3. We

obtain the I-V curve by varying the resistance R and using the ammeter to measure the current

for each resistance value. It is worth noting that the voltage across the pn-juntion is equal to the

voltage across the adjustable resistance, which is equal to the product of the resistance R and the

current flowing through I.

Figure 3: Electric circuit for experiments with micromachined pn-junction and 63Ni.

Figure 4 displays the I-V curves measured at 30 minutes, 2 hours and 16 hours after pouring the

radioactive source on the microchannels of the pn-junction. As expected, the degradation of the

pn-junction due to the 63Ni is very small. However, to conclusively demonstrate this extreme

would require a longer testing time, comparable to the expected life of the nuclear micro-battery.

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In Figure 4, we observe that the maximum current generated in the micromachined pn-junction

by the 63Ni source, i.e. the short circuit current, is 1.31 nA. In silicon, the generation of one

Electron-Hole Pair (EHP) requires about 3.2 eV, even though its energy gap between the

conduction band and covalence band is just 1.12 eV. So the theoretical maximum current

generated by 64µCi can be calculated as:

Imax = 64 µCi * (3.7*1010 dps) * (17.4 keV) / (3.2 eV) * (1.6*10-19 C) = 2.06*10-9 A = 2.06

nA

According to this estimate, the measured current value is 64.07% of the theoretical maximum

value. This illustrates the effectiveness of making the boron diffused depth around 40µm during

microfabrication, which is approximately the traveling distance of 63Ni beta particles in silicon.

Normal pn-junctions, which have ultra shallow junctions (less than 1µm), would result in very

low currents since most of the beta particles would stop in the p or in the n regions, instead of the

depletion region. On the other hand, the open circuit voltage is very small, only 53 mV. This is

partly due to the large p and n contact resistances. In this particular device, the metal used for the

p contact is gold and for the n contact is aluminum alloy, and both the p and n regions are all

covered by metal (the open circuit voltage for a normal junction-type battery is in the range of

0.2 to 0.5 V). A very effective way of increasing the open circuit voltage in a junction-type

battery is by reducing the contact area. The maximum power can be approximately estimated by:

Pmax = Is * Vo= 1.31 nA * 0.053 V = 0.069 nW

Further research on improving the device design and its performance is still on the way and will

be released in the near future.

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Figure 4: I-V curves for a micromachined pn-junction with 63Ni at different times.

SELF-RECIPROCATING CANTILEVER:

This concept involves a more direct use of the charged particles produced by the decay of the

radioactive source: 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. This concept has been tested experimentally with positive results. Figure 5

shows the experimental setup, in which the charges emitted from the source are collected in the

beam to generate the electrostatic force that drives it. The radioactive source used was 63Ni with

an activity of 1 mCi. The beam is 5 cm × 5 mm, made from 60 µm thick copper. A probe tip is

glued to the beam to better detect and measure the movement of the beam. Both the source and

the beam are mounted on a glass base for electrical insulation. The glass base is clamped so that

the beam itself can only move by bending. The measuring scale is a silicon beam with 3µm

spaced gridlines so that the movement can be measured with a precision of 1.5µm. A CCD

camera connected to a VCR is used to record the movement of the beam and its periodicity. As

the radioactive beta source decays, it emits electrons. The copper beam collects these electrons

from the source, and the source itself would become positively charged since it keeps losing

electrons; therefore, in the ideal case, there would be an electrostatic force applied on the beam

that would bend it. However, in atmospheric conditions, no movement of the beam is observed,

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due to the ionization of the surrounding air. For that reason, the experiment has been performed

under vacuum (typically from 30 mTorr to 50 mTorr), where there is no extraneous ionization

and the bending of the beam can be observed.

Figure 5: Self-Reciprocating Cantilever Experimental Set-up

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.

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REFERENCES

https://en.wikipedia.org/wiki/Microelectromechanical_systems

https://www.mems-exchange.org/MEMS/processes/

https://en.wikipedia.org/wiki/Nuclear_micro-battery

" Standards For Protection Against Radiation". Title 10, Code of Federal Regulations,

Part 20, Nuclear Regulatory Commission, Washington, D.C. Continuosly updated.

(http://www.nrc.gov/NRC/CFR/PART020/).

https://www.mems-exchange.org/MEMS/what-is.html

P.Rappaport, and J.J.Loferski, “Thresholds for Electron Bombardment Induced Lattice

Displacements in Si and Ge,” Phys. Rev., Vol.100,p.1261,November,1955