Figure 9 In the MHD duct (a), the electrons in the hot plasma move to the right under influence of force F in the magnetic field B. The electrons collected by the right-hand side of the duct are carried to the load. In a wire in the armature of a conventional generator (b) the electrons are forced to the right by the magnetic field.
- a
- MHD Duct
- HOT PLASMA IN
- COOL GAS OUT TO RADIATOR
- Magnetic Field
- LOAD
- ELECTRONS
- b
- CONVENTIONAL GENERATOR
- SHAFT
- LOAD
- Magnetic Field
- ARMATURE WIRE
- ELECTRONS
In the conventional dynamic generator, an electromotive force is created in a wire that cuts through magnetic lines of force, as shown in Figure 9b. It may be helpful to visualize the conduction electrons as leaving one end of the wire and moving to the other under the influence of the magnetic field.
The force on the electrons in the wire is given by
F = qvB
where
F = the force (in newtons[10])
q = the charge on the electron (1.6 × 10⁻¹⁹ coulomb)
v = the wire’s velocity (in meters per second)
B = the magnetic field strength (in webers per square meter[10])
The surge of electrons along the length of the wire sets up a voltage difference across the ends of the wire. A generator uses this difference to convert the kinetic energy of the moving wire or armature into electrical energy. The wire is kept spinning by the shaft which is connected to a turbine driven by steam or water.
Let us try to eliminate the moving part, the generator armature. What we need is a moving conductor that has no shaft, no bearings, no wearing parts. The substance that meets these requirements is the plasma. Examine Figure 9a. The MHD generator substitutes a moving, conducting gas for the wires. Under the influence of an external magnetic field, the conduction electrons move through the plasma to one side of the duct which carries electrical power away to the load.
The MHD generator gets its energy from an expanding, hot gas; but, unlike the turbogenerator, the heat engine and generator are united in the static duct. The gradual widening of the duct shown in Figure 9a reflects the lower pressure, cooler plasma at the duct’s end. Some of the plasma’s thermal energy content has been tapped off by the duct’s electrodes as electrical power.
The Fourth State of Matter
Plasma can be created by temperatures over 2000°K. At this temperature many high-velocity gas atoms collide with enough energy to knock electrons off each other and thus become ionized. The material thus created, shown as a glowing gas in Figure 10, does not behave consistently as any of the three familiar states of matter: solid, liquid, or gas. Plasma has been called a fourth state of matter. Since we have difficulty in containing such high temperatures on earth, we adopt the strategy of seeding. In this technique gases that are ordinarily difficult to ionize, like helium, are made conducting by adding a fraction of a percent of an alkali metal such as potassium. Alkali metal atoms have loosely bound outer electrons and quickly become ionized at temperatures well below 2000°K.
Figure 10 Glowing plasma in experimental device at General Atomic’s John Jay Hopkins Laboratory, San Diego. T-shaped plasma gun provides data for research in thermonuclear fusion. Courtesy Texas Atomic Energy Research Foundation.
A helium-potassium mixture is a good enough conductor for use in an MHD generator. In this plasma the electrons move rapidly under the influence of the applied fields, though not as well as in metals. The positive ions move in the opposite direction from the electrons, but the electrons are much lighter and move thousands of times faster thus carrying the bulk of the electrical current.
MHD Power Prospects
The MHD duct is not a complete power plant in itself because, after leaving the duct, the stream of gas must be compressed, heated, and returned to the duct. Very high temperature materials and components must be developed for this kind of service. Moreover, while the duct is simple in concept, it must operate at very high temperatures in the presence of the corrosive alkali metals. This presents us with difficult materials problems. When the problems are solved, probably within the next decade, MHD power plants should be able to provide reliable power with high efficiency. They may then serve in large space power plants, and, most important, they may provide cheaper electricity for general use through their higher temperatures and greater efficiencies.
CHEMICAL BATTERIES
Electricity from the Chemical Bond
If you vigorously knead a lemon to free the juices and then stick a strip of zinc in one end and a copper strip in the other, you can measure a voltage across the strips. Electrons will flow through the load without the inconvenience of having to supply heat. You have made yourself a chemical battery.
The chemical battery was the first direct conversion device. Two hundred years ago it was the scientists’ only continuous source of electricity.
Since the chemical battery does not need heat for its operation, it is logical to ask what makes the current flow. Where does the energy come from?
The battery has no semiconductors, but, like the thermoelectric couple and the thermionic diode, it uses dissimilar materials for its electrodes. A conducting fluid or solid is also present to provide for the passage of current between the electrodes. In the example of the lemon, the copper and zinc are the dissimilar electrodes, and the lemon juice is the conducting fluid or electrolyte that supplies positive and negative ions. The battery derives its energy from its complement of chemical fuel. The voltage difference arises because of the different strengths of the chemical bonds. The chemical bond is basically an electrostatic one; some atoms have stronger electrical affinities than others.
Chemical Reactions Used in Batteries and Fuel Cells
Consider the following chemical reactions of common batteries together with some fuel cell reactions which will be discussed further in the next section.
- Battery Reactions
- Pb + PbO₂ + 2H₂SO₄ ⇔ 2PbSO₄ + 2H₂O
- Fe + NiO₂ ⇔ FeO + NiO
- Zn + AgO + H₂O ⇔ Ag + Zn(OH)₂
- Pb + Ag₂O ⇔ PbO + 2Ag
- Fuel Cell Reactions
- 2LiH ⇔ 2Li + H₂
- 2CuBr₂ ⇔ 2CuBr + Br₂
- 2H₂ + O₂ ⇔ 2H₂O (Bacon cell)
- PbI₂ ⇔ Pb + I₂
In principle all these reactions are the same as those going on inside the lemon, although each type of cell produces a slightly different voltage because of the varying chemical affinities of the atoms and molecules involved. There are literally hundreds of materials which can be used for electrolytes and electrodes.
No heat needs to be added as the electrostatic chemical bonds are broken and remade in a battery to generate electrical power. The chemical reaction energy is transferred to the electrical load with almost 100% efficiency. The Carnot cycle is no limitation here; only “cold” electrostatic forces are in action. The reactions cannot go on forever, however, because the battery supplies the energy converter with a very limited supply of fuel. Eventually the fuel is consumed and the voltage drops to zero. This deficiency is remedied by the fuel cell in which fuel is supplied continuously.
An Old Standby in Outer Space
Almost every satellite and space vehicle has a chemical battery aboard. It is not there so much for continuous power production but as a rechargeable electrical accumulator or reservoir to provide electricity during peak loads. The battery is also needed to store energy for use during the periods when solar cells are in the earth’s shadow and therefore inoperative. In this capacity the dependable old battery serves the most modern science very well indeed.
THE FUEL CELL: A CONTINUOUSLY FUELED BATTERY
Potential Fuels
The battery has a very close relative, the fuel cell. Unlike the battery the fuel cell has a continuous supply of fuel.
Figure 11 This diagram shows how a hydrogen-oxygen fuel cell works. The chemical battery works in the same way, except that the chemicals are different and are not continuously supplied from outside the cell. The water produced by the H-O cell shown can be used for drinking on spaceships.
- ANODE H₂ IN
- CATHODE O₂ IN
- ELECTRONS
- LOAD
- KOH ELECTROLYTE
- K⁺ ION
- OH⁻ ION
- NEGATIVE ION FLOW
- 40H⁻ + 2H₂ ⇒ 4H₂O + 4e
- O₂ + 2H₂O + 4e ⇒ 40H⁻
The hydrogen-oxygen cell of Figure 11 is typical of all fuel cells. It essentially burns hydrogen and oxygen to form water. If the hydrogen and oxygen can be supplied continuously and the excess water drained off, we can greatly extend the life of the battery. The fuel cell accomplishes this. Fueled electrical cell would be more descriptive since the physical principles are identical with those of the battery.
Perhaps the most challenging task contemplated for the fuel cell is to bring about the consumption of raw or slightly processed coal, gas, and oil fuels with atmospheric oxygen. If fuel cells can be made to use these abundant fuels, then the high natural conversion efficiency of the fuel cells will make them economically superior to the lower efficiency steam-electric plants now in commercial service.
So far we have dwelt on the fuel cell as a cold energy conversion device that is not limited by the Carnot efficiency. A variation on this theme is possible. Take a hydrogen iodide (HI) cell, and heat the HI to 2000°K. Some of the HI molecules will collide at high velocities and dissociate into hydrogen and iodine: 2HI = H₂ + I₂; the higher the temperature, the more the dissociation. By separating the hydrogen and iodine gases and returning them for recycling to the fuel cell where they are recombined, we have eliminated the fuel supply problem and created a regenerative fuel cell. We have, however, also reintroduced the heat engine and the Carnot cycle efficiency. The thermally regenerative fuel cell is a true heat engine using a dissociating gas as the working fluid.
Scheme for Project Apollo
Most of the impetus for developing the fuel cell as a practical device comes from the space program. The cell has admirable properties for space missions that are less than a few months in duration. It is a clean, quiet, vibrationless source of energy. Like the battery it has a high electrical overload capacity for supplying power peaks and is easily controlled. It can even provide potable water for a crew if the Bacon H - O cell is used. For short missions where large fuel supplies are not needed, it is also among the lightest power plants available.
These compelling advantages have led the National Aeronautics and Space Administration to choose the fuel cell for some of the first manned space ventures. Project Apollo, the manned lunar landing mission, is the most notable example. Here the fuel cell will be not only an energy source, but also part of the ecological cycle which keeps the crew alive.
Problem 4
A manned space vehicle requires an average of 2 electrical kilowatts. A nuclear reactor thermoelectric plant having a mass of 1000 kilograms, including shielding, can supply this power for 10,000 hours. The basic fuel cell has a mass of 50 kilograms and consumes ½ kilogram of chemicals per hour. The chemical containers weigh 25 kilograms. What is the longest mission where the total weight of the fuel cell will be less than the weight of the nuclear power plant?
SOLAR CELLS
Photons as Energy Carriers
All our fossil fuels, such as coal and oil, owe their existence to the solar energy stream that has engulfed the earth for billions of years. The power in this stream amounts to about 1400 watts per square meter at the earth, nearly enough to supply an average home if all the energy were converted to electricity. The problem is to get the sun’s rays to yield up their energy with high efficiency.
The sun’s visible surface has a temperature around 6000°K. Any object heated to this temperature will radiate visible light mostly in the yellow-green portion of the spectrum (5500 A[11]). Our energy conversion device should be tuned to this wavelength.
The energy packets arriving from the sun are called photons. They travel, of course, at the speed of light, and each carries an amount of energy given by
E = hf = hc/λ
where
E = energy (in joules)
h = Planck’s constant (6.62 × 10⁻³⁴ joule-second)
f = the light’s frequency (in cycles per second = c/λ)
c = the velocity of light (300,000,000 meters per second)
λ = the wavelength (in meters)
Using the fact that an angstrom unit is 10⁻¹⁰ meter, the energy of a 5500 A photon could be calculated as
E = hf = hc/λ = (6.62 × 10⁻³⁴ × 3.00 × 10⁸)/(5.50 × 10⁻⁷)
= 3.61 × 10⁻¹⁹ joule = 2.2 electron volts
Comparing this result, 2.2 electron volts, with the energies required to cause atomic ionization or molecular dissociation (an electron volt or so), we see that it is in the right range to actuate direct conversion devices based on such phenomena.
Harnessing the Sun’s Energy
Historically, the sun’s energy has most often been used by concentrating it with a lens or mirror and then converting it to heat. We could do this and run a heat engine, but a more direct avenue is open.
About a decade ago it was found that the junction between p and n semiconductors would generate electricity if illuminated. This discovery led to the development of the solar cell, a thin, lopsided sandwich of silicon semiconductors. As shown in Figure 12, the top semiconductor layer exposed to the sun is extremely thin, only 2.5 microns. Solar photons can readily penetrate this layer and reach the junction separating it from the thick main body of the solar cell.
Figure 12 THE SOLAR CELL
The photograph shows the solar cell in use
on a satellite. The spherical, radioisotope, thermoelectric
generator at the bottom of the satellite is used to supplement
the solar cells. In the solar cell, hole-electron pairs
are created by solar photons in the vicinity of a p-n junction.
Courtesy U. S. Air Force and National Aeronautics and Space Administration.
- p SILICON
- n SILICON
- ELECTRON-MOLE PAIRS
- JUNCTION
- PHOTONS FROM SUN OR RADIOISOTOPE
- ELECTRONS
- ENERGY OUT
Whenever p- and n-type semiconductors are sandwiched together a voltage difference is created across the junction. The separated holes and electrons in the two semiconductor regions establish this electric field across the junction. Unfortunately, there are usually no current carriers in the immediate vicinity of the junction so that no power is produced.
The absorption of solar photons in the vicinity of the junction will create current carriers, as the photons’ energy is transformed into the potential energy of the hole-electron pairs. These pairs would quickly recombine and give up their newly acquired potential energy if the electric field existing across the junction did not whisk them away to an external load.
The solar cell produces electricity when hole-electron pairs are formed. Any other phenomenon that creates such pairs will also generate electricity. The source of energy is irrelevant so long as the current carriers are formed near the junction. Thus, particles emitted by radioactive atoms can also produce electricity from solar cells, although too much bombardment by such particles can damage the cell’s atomic structure and reduce its output.
The solar cell is not a heat engine. Yet it loses enough energy so that the sun’s energy is converted at less than 15% efficiency. Losses commonly occur because of the recombination of the hole-electron pairs before they can produce current, the absorption of photons too far from the junction, and the reflection of incident photons from the top surface of the cell. Despite these losses solar cells are now the mainstay of nonpropulsive space power.
NUCLEAR BATTERIES
Energy from Nuclear Particles
As we have seen, solar cells are able to convert the kinetic energy of charged nuclear particles directly into electricity, but a simpler and more straightforward way of doing this exists. This involves direct use of the flow of charged particles as current.
The nuclear battery shown in Figure 13 performs this trick. A central rod is coated with an electron-emitting radioisotope (a beta-emitter; say, strontium-90). The high-velocity electrons emitted by the radioisotope cross the gap between the cylinders and are collected by a simple metallic sleeve and sent to the load. Simple, but why don’t space charge effects prevent the electrons from crossing the gap as they do in the thermionic converter? The answer lies in the fact that the nuclear electrons have a million times more kinetic energy than those boiled off the thermionic converter’s emitter surface. Consequently, they are too powerful to be stopped by any space charge in the narrow gap.
Nuclear batteries are simple and rugged. They generate only microamperes of current at 10,000 to 100,000 volts.
Figure 13 A NUCLEAR BATTERY
The nuclear battery
depends upon the emission of
charged particles from a surface
coated with a radioisotope. The
particles are collected on another
surface.
- ENERGY OUT
- INSULATOR
- LAYER OF BETA-EMITTING RADIOISOTOPE
- VACUUM
Double Conversion
In the earlier description of the energy conversion matrix, we saw that we could go through the energy transformation process repeatedly until we obtained the kind of energy we wanted. This is exemplified in a type of nuclear battery which uses the so-called double conversion approach. First, the high-velocity nuclear particles are absorbed in a phosphor which emits visible light. The photons thus produced are then absorbed in a group of strategically placed solar cells, which deliver electrical power to the load. Although efficiency is lost at each energy transformation, the double conversion technique still ends up with an overall efficiency of from 1 to 5%, an acceptable value for power supplies in the watt and milliwatt ranges.
ADVANCED CONCEPTS
Ferroelectric and thermomagnetic conversion are subtle concepts which depend upon the gross alteration of a material’s physical properties by the application of heat. Devices employing such concepts are true heat engines. Instead of the gaseous and electronic working fluids used in the other direct conversion concepts, the ferroelectric and thermomagnetic concepts employ patterns of atoms and molecules that are actually rearranged periodically by heat.
Ferroelectric Conversion
Ferroelectric conversion makes use of the peculiar properties of dielectric[12] materials. Barium titanate, for example, has good dielectric properties at low temperatures, but, when its temperature is raised to more than 120°C, the properties get worse rapidly. We cannot discuss dielectric behavior thoroughly in this booklet; suffice it to say that in this process heat is absorbed in a realignment of molecules within the barium titanate latticework.
If we now place a slab of barium titanate between the two plates of an electrical condenser and charge the condenser, as shown in Figure 14, we have a unique way of converting heat into electricity directly. When the barium titanate is heated above its Curie point[13] of 120°C, the condenser’s capacitance is radically reduced as the dielectric constant falls. The condenser is forced to discharge and move electrons through an external circuit consisting of the load and the original source of charge. Useful electrical energy is delivered during this step. Figure 14 shows the process schematically and mathematically. When the dielectric is cooled, waste heat is given up by the barium titanate, and the cycle is complete.
Figure 14 FERROELECTRIC ENERGY CONVERSION
The ferroelectric converter is really an electrical capacitor
whose capacitance is changed by temperature. When heat is
added, capacitance drops, voltage rises, and the capacitor is made to
discharge through the load. CYCLE: ① Switch #1 closed, #2 open.
Condenser charges from battery to charge Q₂ at voltage V₁ with capacity
C₁. ② All switches open. Heat added, capacity changes from
C₁ to C₂, charge remains constant, so voltage changes from V₁ to V₂.
③ Switch #2 closed, #1 open. Condenser discharges through load and
battery to charge Q₁ at voltage V₁ with capacity C₂. ④ All switches
open. Heat rejected, capacity changes from C₂ to C₁, charge remains
constant, so voltage changes from V₁ to V₀. CYCLE THEN REPEATS.
Energy supplied from battery each cycle is E₁. Energy delivered to
load and battery each cycle is E₂. Net energy converted is then E₂ - E₁,
the difference in the shaded areas.
- (a) CIRCUIT
- HEAT IN
- BARIUM TITANATE DIELECTRIC
- WASTE HEAT OUT
- SWITCH #2
- LOAD
- SWITCH #1
- BATTERY
- (b) CYCLE DIAGRAM
- charge
- volts
- Q₂, Q₁, E₁, E₂, V₀ V₁ V₂
- GENERAL INFORMATION:
- C₂ < C₁
- V = Q/C
Thermomagnetic Conversion
The analog[14] of ferroelectricity is ferromagnetism. A converter employing similar principles to those in ferroelectricity can be made using an electrical inductance with a ferromagnetic core. When the temperature of the ferromagnetic material is raised above its Curie point, its magnetic permeability drops quickly, causing the magnetic field to collapse partially. Energy may be delivered to an external load during this change. Instead of energy being stored in an electrostatic field, it is stored in a magnetic field.
Ferroelectric and thermomagnetic conversion both represent a class of energy transformations which involve internal molecular or crystalline rearrangements of solids. There is no change of phase as in a steam engine, but the energy changes are there nevertheless. In thermodynamics such internal geometrical changes are called second-order transitions, as opposed to the first-order transitions observed with heat engines using two-phase working fluids like water/steam.
On the Frontier
Other potential energy conversion schemes are being investigated by scientists and engineers. Those listed in the Energy Conversion Matrix (Figure 2) only scratch the surface.
In particular, we are just learning how to manipulate photons. There are photochemical, photoelectric, and even photomechanical transformations. These have hardly been tapped.
Consider the reaction when an electron and its antimatter equivalent, the positron, meet. They mutually annihilate each other in a burst of energy! This energy will be harnessed someday.
What energy conversion device are we going to use to completely convert mass into energy? The energy requirements for interstellar exploration are so great that these voyages will be impossible unless a new device is found that can completely transform mass into energy.
Then again, we haven’t the faintest idea of how to control gravitational energy, but we may learn.
The panorama is endless.
Problem 5
A 1,000,000-kilogram spaceship takes off for Alpha Centauri, our nearest star, 4.3 light years away. If it accelerates to nine-tenths the velocity of light, what is its kinetic energy? How much fuel mass will have to be completely converted to energy to acquire this velocity?
SUGGESTED REFERENCES
Articles
Fuel Cells, Leonard G. Austin, Scientific American, 201: 72 (October 1959). A survey of the different types.
Nuclear Power in Outer Space, William R. Corliss, Nucleonics, 18: 58 (August 1960). A review of all nuclear space power plants.
Fuel Cells for Space Vehicles, M. G. Del Duca, Astronautics, 5: 36 (March 1960).
Fuel Cells, E. Gorin and H. L. Recht, Chemical Engineering Progress, 55: 51 (August 1959).
Thermionic Converters, Karl G. Hernqvist, Nucleonics, 17: 49 (July 1959).
The Revival of Thermoelectricity, Abram F. Joffe, Scientific American, 199: 31 (November 1958). Excellent historical and technical review.
The Photovoltaic Effect and Its Utilization, P. Rappaport, RCA Review, 20: 373 (September 1959). Recommended for advanced students.
The Prospects of MHD Power Generation, Leo Steg and George W. Sutton, Astronautics, 5: 22 (August 1960).
Conversion of Heat to Electricity by Thermionic Emission, Volney C. Wilson, Journal of Applied Physics, 30: 475 (April 1959). Recommended for advanced students.
Improved Solar Cells Planned for IMP-D, R. D. Hibben, Aviation Week & Space Technology, 83: 53 (July 26, 1965).
Thin-film Solar Cells Boost Output Ratio, P. J. Klass, Aviation Week & Space Technology, 83: 67 (November 29, 1965).
Books
Direct Conversion of Heat to Electricity, Joseph Kaye and John A. Welsh, John Wiley & Sons, Inc., New York 10016, 1960, 387 pp., $11.50. Recommended for advanced students.
Selected Papers on New Techniques for Energy Conversion, Sumner N. Levine, (Ed.), Dover Publications, Inc., New York 10014, 1961, 444 pp., $3.00. A reprinting of many classical papers on direct conversion.
Energy Conversion for Space Power, Nathan W. Snyder, (Ed.), Academic Press, Inc., New York 10003, 1961, 779 pp., $8.50. A collection of American Rocket Society papers.
Man and Energy, Alfred Rene Ubbelohde, George Braziller, New York 10016, 1955, 247 pp., $5.00 (hardback); $1.25 (paperback), from Penguin Books, Inc., Baltimore, Maryland 21211. A popular treatment of energy and power.
Motion Pictures
The following films are produced by Educational Services, Inc., and are available from Modern Learning Aids, A Division of Modern Talking Picture Service, Inc., 3 East 54th St., New York 22, New York.
Energy and Work, 0311, 29 minutes, $150.
Mechanical Energy and Thermal Energy, 0312, 27 minutes, $120.
Conservation of Energy, 0313, 27 minutes, $150.
Photo-Electric Effect, 0417, 28 minutes, $220.
ANSWERS TO PROBLEMS
First, mechanical energy drives the car’s electric generator. Second, the electrical energy is converted into chemical energy when the battery is recharged.
From the kinetic energy equation we get
v = √(2 E/m)
Since the engine is 25% efficient, the energy available to propel the car is 48,000 × 0.25 or 12,000 joules. So
v = √(24,000/1,000) = 2√6 = 4.9 meters per second
e = (300 - 20)/300 = 14/15 = 0.93 = 93%
The crossover point, t, in hours is found by equating the nuclear power plant mass and that of the fuel cell with its associated fuel. The equation is
1000 = 50 + 25 + ½t t = 1850 hours = 77 days
E = ½ mv² = (10⁶(0.9 × 3 × 10⁸)²)/2 = 3.6 × 10²² joules
The ship will use the same amount of energy to decelerate at its destination. Note that this calculation assumes a perfect efficiency in converting the energy of matter annihilation into the kinetic energy of the space ship. The mass consumed is
m = E/c² = (3.6 × 10²²)/(9 × 10¹⁶) = 4.0 × 10⁵ kg
almost half the spaceship mass.
Footnotes
This booklet is one of the “Understanding the Atom” Series. Comments are invited on this booklet and others in the series; please send them to the Division of Technical Information, U. S. Atomic Energy Commission, Washington, D. C. 20545.
Published as part of the AEC’s educational assistance program, the series includes these titles:
Accelerators
Animals in Atomic Research
Atomic Fuel
Atomic Power Safety
Atoms at the Science Fair
Atoms in Agriculture
Atoms, Nature, and Man
Careers in Atomic Energy
Computers
Controlled Nuclear Fusion
Cryogenics, The Uncommon Cold
Direct Conversion of Energy
Fallout From Nuclear Tests
Food Preservation by Irradiation
Genetic Effects of Radiation
Index to the UAS Series
Lasers
Microstructure of Matter
Neutron Activation Analysis
Nondestructive Testing
Nuclear Clocks
Nuclear Energy for Desalting
Nuclear Power and Merchant Shipping
Nuclear Power Plants
Nuclear Propulsion for Space
Nuclear Reactors
Nuclear Terms, A Brief Glossary
Our Atomic World
Plowshare
Plutonium
Power from Radioisotopes
Power Reactors in Small Packages
Radioactive Wastes
Radioisotopes and Life Processes
Radioisotopes in Industry
Radioisotopes in Medicine
Rare Earths
Reading Resources in Atomic Energy
Research Reactors
SNAP, Nuclear Space Reactors
Sources of Nuclear Fuel
Synthetic Transuranium Elements
The Atom and the Ocean
The Chemistry of the Noble Gases
The First Reactor
Whole Body Counters
Your Body and Radiation
A single copy of any one booklet, or of no more than three different booklets, may be obtained free by writing to:
USAEC, P. O. BOX 62, OAK RIDGE, TENNESSEE 37830
Complete sets of the series are available to school and public librarians, and to teachers who can make them available for reference or for use by groups. Requests should be made on school or library letterheads and indicate the proposed use.
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Printed in the United States of America
USAEC Division of Technical Information Extension, Oak Ridge, Tennessee
May 1968
Transcriber’s Notes
- Silently corrected a few typos.
- Modified some image references to reflect the pageless flowable eBook format.
- Retained publication information from the printed edition: this eBook is public-domain in the country of publication.
- In the text versions only, text in italics is delimited by _underscores_.