Worlds Within Worlds: The Story of Nuclear Energy, Volume 3 (of 3) - 3

However effective a fusion bomb may be in liberating vast quantities of
energy, it is not what one has in mind when speaking of a fusion power
station. The energy of a fusion bomb is released all at once and its
only function is that of utter destruction. What is wanted is the
production of fusion energy at a low and steady rate—a rate that is
under the control of human operators.
The sun, for instance, is a vast fusion furnace 866,000 miles across,
but it is a controlled one—even though that control is exerted by the
impersonal laws of nature. It releases energy at a very steady and very
slow rate. (The rate is not slow in human terms, of course, but stars
sometimes do release their energy in a much more cataclysmic fashion.
The result is a “supernova” in which for a short time a single star will
increase its radiation to as much as a trillion times its normal level.)
The sun (or any star) going at its normal rate is controlled and steady
in its output because of the advantage of huge mass. An enormous mass,
composed mainly of hydrogen, compresses itself, through its equally
enormous gravitational field, into huge densities and temperatures at
its center, thus igniting the fusion reaction—while the same
gravitational field keeps the sun together against its tendency to
expand.
There is, as far as scientists know, no conceivable way of concentrating
a high gravitational field in the absence of the required mass, and the
creation of controlled fusion on earth must therefore be done without
the aid of gravity. Without a huge gravitational force we cannot
simultaneously bring about sun-center densities and sun-center
temperatures; one or the other must go.
On the whole, it would take much less energy to aim at the temperatures
than at the densities and would be much more feasible. For this reason,
physicists have been attempting, all through the nuclear age, to heat
thin wisps of hydrogen to enormous temperature. Since the gas is thin,
the nuclei are farther apart and collide with each other far fewer times
per second. To achieve fusion ignition, therefore, temperatures must be
considerably higher than those at the center of the sun. In 1944 Fermi
calculated that it might take a temperature of 50,000,000° to ignite a
hydrogen-3 fusion with hydrogen-2 under earthly conditions, and
400,000,000° to ignite hydrogen-2 fusion alone. To ignite hydrogen-1
fusion, which is what goes on in the sun (at a mere 15,000,000°),
physicists would have to raise their sights to beyond the billion-degree
mark.
[Illustration: _A supernova photographed on March 10, 1935._]
[Illustration: _The same star on May 6._]
This would make it seem almost essential to use hydrogen-3 in one
fashion or another. Even if it can’t be prepared in quantity to begin
with, it might be formed by neutron bombardment of lithium, with the
neutrons being formed by the fusion reaction. In this way, you would
start with lithium and hydrogen-2 plus a little hydrogen-3. The
hydrogen-3 is formed as fast as it is used up. Although in the end
hydrogen is converted to helium in a controlled fusion reaction as in
the sun, the individual steps in the reaction under human control are
quite different from those in the sun.
Still, even the temperatures required for hydrogen-3 represent an
enormous problem, particularly since the temperature must not only be
reached, but must be held for a period of time. (You can pass a piece of
paper rapidly through a candle flame without lighting it. It must be
held in the flame for a short period to give it a chance to heat and
ignite.)
The English physicist John David Lawson (1923- ) worked out the
requirements in 1957. The time depended on the density of the gas. The
denser the gas, the shorter the period over which the temperature had to
be maintained. If the gas is about one hundred-thousand times as dense
as air, the proper temperature must be held, under the most favorable
conditions, for about one thousandth of a second.
There are a number of different ways in which a quantity of hydrogen can
be heated to very high temperatures—through electric currents, through
magnetic fields, through laser beams and so on. As the temperature goes
up into the tens of thousands of degrees, the hydrogen atoms (or any
atoms) are broken up into free electrons and bare nuclei. Such a mixture
of charged particles is called a “plasma”. Ever since physicists have
begun to try to work with very hot gases, with fusion energy in mind,
they have had to study the properties of such “plasma”, and a whole new
science of “plasma physics” has come into existence.
But if you do heat a gas to very high temperatures, it will tend to
expand and thin out to uselessness. How can such a super-hot gas be
confined in a fixed volume without an enormous gravitational field to
hold it together?
An obvious answer would be to place it in a container, but no ordinary
container of matter will serve to hold the hot gas. You may think this
is because the temperature of the gas will simply melt or vaporize
whatever matter encloses it. This is not so. Although the gas is at a
very high temperature, it is so thin that it has very little total heat.
It does not have enough heat to melt the solid walls of a container.
What happens instead is that the hot plasma cools down the moment it
touches the solid walls and the entire attempt to heat it is ruined.
What’s more, if you try to invest the enormous energies required to keep
the plasma hot despite the cooling effect of the container walls, then
the walls will gradually heat and melt. Nor must one wait for the walls
to melt and the plasma to escape before finding the attempt at fusion
ruined. Even as the walls heat up they liberate some of their own atoms
into the plasma and introduce impurities that will prevent the fusion
reaction.
Any material container is therefore out of the question.
Fortunately, there is a nonmaterial way of confining plasma. Since
plasma consists of a mixture of electrically charged particles, it can
experience electromagnetic interactions. Instead of keeping the plasma
in a material container, you can surround it by a magnetic field that is
designed to keep it in place. Such a magnetic field is not affected by
any heat, however great, and cannot be a source of material impurity.
In 1934, the American physicist Willard Harrison Bennett (1903- ) had
worked out a theory dealing with the behavior of magnetic fields
enclosing plasma. It came to be called the “pinch effect” because the
magnetic field pinched the gas together and held it in place.
The first attempt to make use of the pinch effect for confining plasma,
with eventual ignition of fusion in mind, was in 1951 by the English
physicist Alan Alfred Ware (1924- ). Other physicists followed, not
only in Great Britain, but in the United States and the Soviet Union as
well.
The first use of the pinch effect was to confine the plasma in a
cylinder. This, however, could not be made to work. The situation was
too unstable. The plasma was held momentarily, then writhed and broke
up.
[Illustration: _Plasma in a magnetic field._]
[Illustration: _Enormous machines and complex equipment, such as the
Scyllac machine shown above, are required for nuclear fusion research._]
Attempts were made to remove the instability. The field was so designed
as to be stronger at the ends of the cylinder than elsewhere. The
particles in the plasma would stream toward one end or another and would
then bounce back producing a so-called “magnetic mirror”.
In 1951 the American physicist Lyman Spitzer, Jr. (1914- ) had worked
out the theoretical benefits to be derived from a container twisted into
a figure-eight shape. Eventually, such devices were built and called
“stellarators” from the Latin word for “star”, because it was hoped that
it would produce the conditions that would allow the sort of fusion
reactions that went on in stars.
All through the 1950s and 1960s, physicists have been slowly inching
toward their goal, reaching higher and higher temperatures and holding
them for longer and longer periods in denser and denser gases.
In 1969 the Soviet Union used a device called “Tokamak-3” (a Russian
abbreviation for their phrase for “electric-magnetic”) to keep a supply
of hydrogen-2, a millionth as dense as air, in place while heating it to
tens of millions of degrees for a hundredth of a second.
A little denser, a little hotter, a little longer—and controlled fusion
might become possible.[5]


BEYOND FUSION

Antimatter
Is there anything that lies beyond fusion?
When hydrogen undergoes fusion and becomes helium, only 0.7% of the
original mass of the hydrogen is converted to energy. Is it possible to
take a quantity of mass and convert all of it, every bit, to energy?
Surely that would be the ultimate energy source. Mass for mass, that
would deliver 140 times as much energy as hydrogen fusion would; it
would be as far beyond hydrogen fusion as hydrogen fusion is beyond
uranium fission.
And, as a matter of fact, total annihilation of matter is conceivable
under some circumstances.
In 1928 the English physicist Paul Adrien Maurice Dirac (1902- )
presented a treatment of the electron’s properties that made it appear
as though there ought also to exist a particle exactly like the electron
in every respect except that it would be opposite in charge. It would
carry a positive electric charge exactly as large as the electron’s
negative one.
If the electron is a particle, this suggested positively charged twin
would be an “antiparticle”. (The prefix comes from a Greek word meaning
“opposite”.)
[Illustration: _P. A. M. Dirac_]
[Illustration: _The first picture of the positron (left) was taken in a
Wilson cloud chamber. On the right is C. D. Anderson, the discoverer of
the positron._]
The proton is _not_ the electron’s antiparticle. Though a proton carries
the necessary positive charge that is exactly as large as the negative
charge of the electron, the proton has a much larger mass than the
electron has. Dirac’s theory required that the antiparticle have the
same mass as the particle to which it corresponded.
In 1932 C. D. Anderson was studying the impact of cosmic particles on
lead. In the process, he discovered signs of a particle that left tracks
exactly like those of an electron, but tracks that curved the wrong way
in a magnetic field. This was a sure sign that it had an electric charge
opposite to that of the electron. He had, in short, discovered the
electron’s antiparticle and this came to be called the “positron”.
Positrons were soon detected elsewhere too. Some radioactive isotopes,
formed in the laboratory by the Joliot-Curies and by others, were found
to emit positive beta particles—positrons rather than electrons. When an
ordinary beta particle, or electron, was emitted from a nucleus, a
neutron within the nucleus was converted to a proton. When a positive
beta particle, a positron, was emitted, the reverse happened—a proton
was converted to a neutron.
A positron, however, does not endure long after formation. All about it
were atoms containing electrons. It could not move for more than a
millionth of a second or so before it encountered one of those
electrons. When it did, there was an attraction between the two, since
they were of opposite electric charge. Briefly they might circle each
other (to form a combination called “positronium”) but only very
briefly. Then they collided and, since they were opposites, each
cancelled the other.
The process whereby an electron and a positron met and cancelled is
called “mutual annihilation”. Not everything was gone, though. The mass,
in disappearing, was converted into the equivalent amount of energy,
which made its appearance in the form of one or more gamma rays.
(It works the other way, too. A gamma ray of sufficient energy can be
transformed into an electron and a positron. This phenomenon, called
“pair production”, was observed as early as 1930 but was only properly
understood after the discovery of the positron.)
Of course, the mass of electrons and positrons is very small and the
amount of energy released per electron is not enormously high. Still,
Dirac’s original theory of antiparticles was not confined to electrons.
By his theory, any particle ought to have some corresponding
antiparticle. Corresponding to the proton, for instance, there ought to
be an “antiproton”. This would be just as massive as the proton and
would carry a negative charge just as large as the proton’s positive
charge.
An antiproton, however, is 1836 times as massive as a positron. It would
take gamma rays or cosmic particles with 1836 times as much energy to
form the proton-antiproton pair as would suffice for the
electron-positron pair. Cosmic particles of the necessary energies
existed but they were rare and the chance of someone being present with
a particle detector just as a rare super-energetic cosmic particle
happened to form a proton-antiproton pair was very small.
[Illustration: _The Bevatron began operation in 1954._]
Physicists had to wait until they had succeeded in designing particle
accelerators that would produce enough energy to allow the creation of
proton-antiproton pairs. This came about in the early 1950s when a
device called the “Cosmotron” was built at Brookhaven National
Laboratory in Long Island in 1952 and another called the “Bevatron” at
the University of California in Berkeley in 1954.
Using the Bevatron in 1956, Segrè (the discoverer of technetium who had,
by that time, emigrated to the United States), the American physicist
Owen Chamberlain (1920- ), and others succeeded in detecting the
antiproton.
The antiproton was as unlikely to last as long as the positron was. It
was surrounded by myriads of proton-containing nuclei and in a tiny
fraction of a second it would encounter one. The antiproton and the
proton also underwent mutual annihilation, but having 1836 times the
mass, they produced 1836 times the energy that was produced in the case
of an electron and a positron.
There was even an “antineutron”, a particle reported in 1956 by the
Italian-American physicist Oreste Piccioni (1915- ) and his
co-workers. Since the neutron has no charge, the antineutron has no
charge either, and one might wonder how the antineutron would differ
from the neutron then. Actually, both have a small magnetic field. In
the neutron the magnetic field is pointed in one direction with
reference to the neutron’s spin; in the antineutron it is pointed in the
other.
[Illustration: _Bubble chamber photograph of an antiproton
annihilation._]
In 1965 the American physicist Leon Max Lederman (1922- ) and his
co-workers produced a combination of an antiproton and an antineutron
that together formed an “antideuteron”, which is the nucleus of
antihydrogen-2.
This is good enough to demonstrate that if antiparticles existed by
themselves without the interfering presence of ordinary particles, they
could form “antimatter”, which would be precisely identical with
ordinary matter in every way except for the fact that electric charges
and magnetic fields would be turned around.
If antimatter were available to us, and if we could control the manner
in which it united with matter, we would have a source of energy much
greater and, perhaps, simpler to produce than would be involved in
hydrogen fusion.
To be sure, there is no antimatter on earth, except for the
submicroscopic amounts that are formed by the input of tremendous
energies. Nor does anyone know of any conceivable way of forming
antimatter at less energy than that produced by mutual annihilation, so
that we might say that mankind can never make an energy profit out of
it—except that with the memory of Rutherford’s prediction that nuclear
energy of any kind could never be tapped, one hesitates to be
pessimistic about anything.

The Unknown
Physical theory makes it seem that particles and antiparticles ought to
exist in the universe in equal quantities. Yet on earth (and, we can be
quite certain, in the rest of the solar system and even, very likely, in
the rest of the galaxy) protons, neutrons, and electrons are common,
while antiprotons, antineutrons, and positrons are exceedingly rare.
Could it be that when the universe was first formed there were indeed
equal quantities of particles and antiparticles but that they were
somehow segregated, perhaps into galaxies and “antigalaxies”? If so,
there might occasionally be collisions of a galaxy and an antigalaxy
with the evolution of vast quantities of energy as mutual annihilation
on a cosmic scale takes place.
There are, in fact, places in the heavens where radiation is unusually
high in quantity and in energy. Can we be witnessing such enormous
mutual annihilation?
Indeed, it is not altogether inconceivable that we may still have new
types of forces and new sources of energy to discover. Until about 1900,
no one suspected the existence of nuclear energy. Are we quite sure now
that nuclear energy brings us to the end, and that there is not a form
of energy more subtle still, and greater?
In 1962, for instance, certain puzzling objects called “quasars” were
discovered far out in space, a billion light-years or more away from us.
Each one shines from 10 to 100 times as brilliantly as an entire
ordinary galaxy does, and yet may be no more than a hundred-thousandth
as wide as a galaxy.
This is something like finding an object 10 miles across that delivers
as much total light as 100 suns.
It is very hard to understand where all that energy comes from and why
it should be concentrated into so tiny a volume. Astronomers have tried
to explain it in terms of the four interactions now known, but is it
possible that there is a fifth greater than any of the four?
If so, it is not impossible that eventually man’s restless brain may
come to understand and even utilize it.


FOOTNOTES

[1]See _The First Reactor_, another booklet in this series.
[2]See _Nuclear Reactors_ and _Nuclear Power Plants_, companion booklets
in this series.
[3]See _Breeder Reactors_, another booklet in this series.
[4]See _Thorium—and the Third Fuel_, another booklet in this series.
[5]See _Controlled Nuclear Fusion_, another booklet in this series.


QUOTATION CREDIT

Inside front cover Copyright © by Abelard-Shuman, Ltd., New York.
Reprinted by permission from _Inside the Atom_,
Isaac Asimov, 1966.


READING LIST

Basic Books
_Basic Laws of Matter_ (revised edition), Harrie S. W. Massey and
Arthur R. Quinton, Herald Books, Bronxville, New York, 1965, 178 pp.,
$3.75. Grades 7-9. A nontechnical presentation of atoms and the laws
governing their behavior.
_Biography of Physics_, George Gamow, Harper & Row, Publishers, New
York, 1961, 338 pp., $6.50 (hardback); $2.75 (paperback). Grades 9-12.
A history of theoretical physics.
_Discoverer of X Rays: Wilhelm Conrad Roentgen_, Arnulf K. Esterer,
Julian Messner, New York, 1968, 191 pp., $3.50. Grades 7-10. This
interesting biography includes a brief, but very helpful, pronouncing
gazetteer of the German, Swiss, and Dutch names in the text.
_Ernest Rutherford: Architect of the Atom_, Peter Kelman and A. Harris
Stone, Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1969, 72
pp., $3.95. Grades 5-7. A well-done biography of this famous atomic
scientist. Many of the drawings illustrate theoretical ideas very well
for the elementary grades. A glossary is included.
_Enrico Fermi: Atomic Pioneer_, Doris Faber, Prentice-Hall, Inc.,
Englewood Cliffs, New Jersey, 1966, 86 pp., $3.95. Grades 5-8. A
biography of the man who built the first reactor.
_Giant of the Atom: Ernest Rutherford_, Robin McKown, Julian Messner,
New York, 1962, 191 pp., $3.50. Grades 7-12. The life and
accomplishments of a great physicist.
_The History of the Atomic Bomb_, Michael Blow, American Heritage
Publishing Company, Inc., New York, 1968, 150 pp., $5.95. Grades 5-9.
This sumptuously illustrated history provides an informative
explanation of nuclear physics in addition to comprehensive coverage
of the bomb’s development and use.
_Inside the Atom_, Isaac Asimov, Abelard-Schuman, Ltd., New York,
1966, 197 pp., $4.00. Grades 7-10. This comprehensive, well-written
text explains nuclear energy and its applications.
_Madame Curie: A Biography_, Eve Curie, translated by Vincent Sheean,
Doubleday and Company, Inc., New York, 1937, 385 pp., $5.95
(hardback); $0.95 (paperback). Grades 9-12. This superb biography,
which won the 1937 National Book Award for Nonfiction, illustrates
dramatically the full spectrum of Marie Curie’s life.
_Men Who Mastered the Atom_, Robert Silverberg, G. P. Putnam’s Sons,
New York, 1965, 193 pp., $3.49. Grades 7-9. Atomic energy history is
told through the work of pioneer scientists from Thales to present-day
researchers.
_The Neutron Story_, Donald J. Hughes, Doubleday and Company, Inc.,
New York, 1959, 158 pp., out of print. Grades 7-9. A substantial and
interesting account of neutron physics.
_Niels Bohr: The Man Who Mapped the Atom_, Robert Silverberg, MacRae
Smith Company, Philadelphia, Pennsylvania, 1965, 189 pp., $3.95.
Grades 8-12. An exciting, suspenseful, and humorous biography of one
of the pioneers in atomic energy. Includes a glossary and references.
_The Questioners: Physicists and the Quantum Theory_, Barbara Lovett
Cline, Crowell Collier and MacMillan, Inc., New York, 1965, 274 pp.,
$5.00 (hardback); available in paperback with the title _Men Who Made
A New Physics: Physicists and the Quantum Theory_, New American
Library, Inc., New York, $0.75. Grades 9-12. An exceptionally
well-delineated and personable account of the development of the
quantum theory by physicists in the first quarter of this century.
_The Restless Atom_, Alfred Romer, Doubleday and Company, Inc., New
York, 1960, 198 pp., $1.25. Grades 9-12. A stimulating nonmathematical
account of the classic early experiments that advanced knowledge about
atomic particles.
_Roads to Discovery_, Ralph E. Lapp, Harper and Row, Publishers, New
York, 1960, 191 pp., out of print. Grades 10-12. Historical survey of
nuclear physics beginning with Roentgen’s discovery of X rays and
concluding with the discoveries of the rare elements.
_Secret of the Mysterious Rays: The Discovery of Nuclear Energy_,
Vivian Grey, Basic Books, Inc., Publishers, New York, 1966, 120 pp.,
$3.95. Grades 4-8. This outstanding history of nuclear research from
Roentgen to Fermi is dramatically presented. The uncertainty of the
unknown, the accidental discovery and the often lengthy and tedious
research are woven in this story of scientists from around the world
who pooled their knowledge and experience to unlock “the secrets of
the mysterious rays”.
_Wilhelm Roentgen and the Discovery of X Rays_, Bern Dibner, Franklin
Watts, Inc., New York, 1968, 149 pp., $2.95. Grades 5-8. This detailed
biography, illustrated with line drawings, historical photographs, and
papers, is a fine addition to Watts’ “Immortals of Science” Series.
_Working with Atoms_, Otto R. Frisch, Basic Books, Inc., New York,
1965, 96 pp., $4.95. Grades 9-12. Dr. Frisch presents a history of
nuclear energy research and provides experiments for the reader. He
gives a personal account of the pioneering work in which he and Lise
Meitner explained the splitting of uranium and introduced the term
“nuclear fission”.

Advanced Books
_An American Genius: The Life of Ernest Orlando Lawrence_, Herbert
Childs, E. P. Dutton and Company, Inc., New York, 1968, 576 pp.,
$12.95. This well-written, scientifically accurate, and very
interesting biography captures the excitement of Lawrence’s life.
Ernest Lawrence was the inventor of the cyclotron, a major member of
the wartime atomic energy development, and the director of the
Lawrence Radiation Laboratory.
_The Atom and Its Nucleus_, George Gamow, Prentice-Hall, Inc.,
Englewood Cliffs, New Jersey, 1961, 153 pp., $1.25. A popular-level
discussion of nuclear structure and the applications of nuclear
energy.
_Atomic Energy for Military Purposes_, Henry D. Smyth, Princeton
University Press, Princeton, New Jersey, 1945, 308 pp., $4.00. A
complete account of the wartime project that developed the first
nuclear weapons and of the considerations that prompted their use.
_Atomic Quest_, Arthur H. Compton, Oxford University Press, Inc., New
York, 1956, 370 pp., $7.95. A personal narrative of the research that
led to the release of atomic energy on a useful scale by a scientist
who played a principal part in the atomic bomb project during World
War II.
_The Atomists_ (_1805-1933_), Basil Schonland, Oxford University
Press, Inc., New York, 1968, 198 pp., $5.60. This book, which can be
understood by anyone who has had a high school physics course,
presents atomic theory development from Dalton through Bohr. It
achieves a good balance between popular treatments and highly
technical works without slighting the technical aspects.
_Atoms in the Family: My Life with Enrico Fermi_, Laura Fermi, Chicago
University Press, Chicago, Illinois, 1954, 267 pp., $5.00 (hardback);
$2.45 (paperback). Laura Fermi writes about her husband, Enrico Fermi,
the physicist who led the group that built the first nuclear reactor.
_The Born-Einstein Letters: The Correspondence Between Albert Einstein
and Max and Hedwig Born from 1916 to 1955_, commentaries by Max Born,
translated by Irene Born, Walker and Company, 1971, 240 pp., $8.50.
These interesting letters reveal the scientific and personal lives of
these two atomic scientists.
_Einstein: His Life and Times_, Philipp Frank, Alfred A. Knopf, Inc.,
New York, 1953, 298 pp., $6.95. A brilliant biography that reveals the
richness of Einstein’s life and work and the tremendous impact he made
upon physics.
_Enrico Fermi, Physicist_, Emilio Segrè, Chicago University Press,
Chicago, Illinois, 1970, 288 pp., $6.95. This biography tells of
Enrico Fermi’s intellectual history, achievements, and his scientific
style. The scientific problems faced or solved by Fermi are explained
in layman’s terms. Emilio Segrè was a friend and scientific
collaborator who worked with Fermi for many years.
_An Introduction to Physical Science: The World of Atoms_ (second
edition), John J. G. McCue, The Ronald Press Company, New York, 1963,
775 pp., $9.50. This textbook was written for college humanities
students.
_J. J. Thomson: Discoverer of the Electron_, George Thomson, Doubleday
and Company, Inc., New York, 1966, 240 pp., $1.45. This biography,
written by J. J. Thomson’s son, describes his research at the famed
Cavendish Laboratory in Cambridge, England.
_John Dalton and the Atom_, Frank Greenaway, Cornell University Press,
Ithaca, New York, 1966, 256 pp., $7.50. A biography for the general
reader and the high school science student. Dalton is famous for his
development of chemical combinations based on atomic theory. This
provided the basis for modern structural theories of chemistry.
_John Dalton and the Atomic Theory: The Biography of a Natural
Philosopher_, Elizabeth C. Patterson, Doubleday and Company, Inc., New
York, 1970, 320 pp., $6.95 (hardback); $1.95 (paperback). The drama of
Dalton’s life—his rigorous self-teaching, scientific work, and