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Title: Worlds Within Worlds: The Story of Nuclear Energy, Volume 3 (of 3) - Nuclear Fission; Nuclear Fusion; Beyond Fusion
Author: Asimov, Isaac
Language: English
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*** Start of this LibraryBlog Digital Book "Worlds Within Worlds: The Story of Nuclear Energy, Volume 3 (of 3) - Nuclear Fission; Nuclear Fusion; Beyond Fusion" ***
Worlds Within Worlds:
The Story of Nuclear Energy
Volume 3
Nuclear Fission · Nuclear Fusion · Beyond Fusion
by Isaac Asimov
United States Atomic Energy Commission
Office of Information Services
Library of Congress Catalog Card Number 75-189477
1972
_Nothing in the history of mankind has opened our eyes to the
possibilities of science as has the development of atomic power. In the
last 200 years, people have seen the coming of the steam engine, the
steamboat, the railroad locomotive, the automobile, the airplane, radio,
motion pictures, television, the machine age in general. Yet none of it
seemed quite so fantastic, quite so unbelievable, as what man has done
since 1939 with the atom ... there seem to be almost no limits to what
may lie ahead: inexhaustible energy, new worlds, ever-widening knowledge
of the physical universe._
Isaac Asimov
[Illustration: Photograph of night sky]
Nuclear energy is playing a vital role in the life of every man, woman,
and child in the United States today. In the years ahead it will affect
increasingly all the peoples of the earth. It is essential that all
Americans gain an understanding of this vital force if they are to
discharge thoughtfully their responsibilities as citizens and if they
are to realize fully the myriad benefits that nuclear energy offers
them.
The United States Atomic Energy Commission provides this booklet to help
you achieve such understanding.
UNITED STATES ATOMIC ENERGY COMMISSION
Dr. James R. Schlesinger, Chairman
James T. Ramey
Dr. Clarence E. Larson
William O. Doub
Dr. Dixy Lee Ray
[Illustration: Isaac Asimov]
ISAAC ASIMOV received his academic degrees from Columbia University and
is Associate Professor of Biochemistry at the Boston University School
of Medicine. He is a prolific author who has written over 100 books in
the past 18 years, including about 20 science fiction works, and books
for children. His many excellent science books for the public cover
subjects in mathematics, physics, astronomy, chemistry, and biology,
such as _The Genetic Code_, _Inside the Atom_, _Building Blocks of the
Universe_, _Understanding Physics_, _The New Intelligent Man’s Guide to
Science_, and _Asimov’s Biographical Encyclopedia of Science and
Technology_. In 1965 Dr. Asimov received the James T. Grady Award of the
American Chemical Society for his major contribution in reporting
science progress to the public.
[Illustration: Photograph of night sky]
CONTENTS
VOLUME 1
Introduction 5
Atomic Weights 6
Electricity 11
Units of Electricity 11
Cathode Rays 13
Radioactivity 17
The Structure of the Atom 25
Atomic Numbers 30
Isotopes 35
Energy 47
The Law of Conservation of Energy 47
Chemical Energy 50
Electrons and Energy 54
The Energy of the Sun 55
The Energy of Radioactivity 57
VOLUME 2
Mass and Energy 69
The Structure of the Nucleus 75
The Proton 75
The Proton-Electron Theory 76
Protons in Nuclei 80
Nuclear Bombardment 82
Particle Accelerators 86
The Neutron 92
Nuclear Spin 92
Discovery of the Neutron 95
The Proton-Neutron Theory 98
The Nuclear Interaction 101
Neutron Bombardment 107
VOLUME 3
Nuclear Fission 117
New Elements 117
The Discovery of Fission 122
The Nuclear Chain Reaction 127
The Nuclear Bomb 131
Nuclear Reactors 141
Nuclear Fusion 146
The Energy of the Sun 146
Thermonuclear Bombs 148
Controlled Fusion 150
Beyond Fusion 158
Antimatter 158
The Unknown 163
Reading List 165
[Illustration: _Enrico Fermi (left) and Niels Bohr discuss physics as
they stroll along the Appian Way outside Rome in 1931._]
NUCLEAR FISSION
New Elements
In 1934 Enrico Fermi began his first experiments involving the
bombardment of uranium with neutrons—experiments that were to change the
face of the world.
Fermi had found that slow neutrons, which had very little energy, were
easily absorbed by atomic nuclei—more easily than fast neutrons were
absorbed, and certainly more easily than charged particles were.
Often what happened was that the neutron was simply absorbed by the
nucleus. Since the neutron has a mass number of 1 and an atomic number
of 0 (because it is uncharged), a nucleus that absorbs a neutron remains
an isotope of the same element, but increases its mass number.
For instance, suppose that neutrons are used to bombard hydrogen-1,
which then captures one of the neutrons. From a single proton, it will
become a proton plus a neutron; from hydrogen-1, it will become
hydrogen-2. A new nucleus formed in this way will be at a higher energy
and that energy is emitted in the form of a gamma ray.
Sometimes the more massive isotope that is formed through neutron
absorption is stable, as hydrogen-2 is. Sometimes it is not, but is
radioactive instead. Because it has added a neutron, it has too many
neutrons for stability. The best way of adjusting the matter is to emit
a beta particle (electron). This converts one of the neutrons into a
proton. The mass number stays the same but the atomic number increases
by one.
The element rhodium, for example, which has an atomic number of 45, has
only 1 stable isotope, with a mass number of 103. If rhodium-103 (45
protons, 58 neutrons) absorbs a neutron, it becomes rhodium-104 (45
protons, 59 neutrons), which is not stable. Rhodium-104 emits a beta
particle, changing a neutron to a proton so that the nuclear combination
becomes 46 protons and 58 neutrons. This is palladium-104, which is
stable.
[Illustration: _Fermi’s laboratory in Rome in 1930._]
As another example, indium-115 (49 protons, 66 neutrons) absorbs a
neutron and becomes indium-116 (49 protons, 67 neutrons), which gives
off a beta particle and becomes tin-116 (50 protons, 66 neutrons), which
is stable.
There are over 100 isotopes that will absorb neutrons and end by
becoming an isotope of an element one higher in the atomic number scale.
Fermi observed a number of these cases.
Having done so, he was bound to ask what would happen if uranium were
bombarded with neutrons. Would its isotopes also be raised in atomic
number—in this case from 92 to 93? If that were so it would be very
exciting, for uranium had the highest atomic number in the entire scale.
Nobody had ever discovered any sample of element number 93, but perhaps
it could be formed in the laboratory.
In 1934, therefore, Fermi bombarded uranium with neutrons in the hope of
obtaining atoms of element 93. Neutrons were absorbed and whatever was
formed did give off beta particles, so element 93 should be there.
However, four different kinds of beta particles (different in their
energy content) were given off and the matter grew very confusing. Fermi
could not definitely identify the presence of atoms of element 93 and
neither could anyone else for several years. Other things turned up,
however, which were even more significant.
Before going on to these other things, however, it should be mentioned
that undoubtedly element 93 was formed even though Fermi couldn’t
clearly demonstrate the fact. In 1939 the American physicists Edwin
Mattison McMillan (1907- ) and Philip Hauge Abelson (1913- ),
after bombarding uranium atoms with slow neutrons, were able to identify
element 93. Since uranium had originally been named for the planet,
Uranus, the new element beyond uranium was eventually named for the
planet Neptune, which lay beyond Uranus. Element 93 is therefore called
“neptunium”.
[Illustration: _Lise Meitner_]
[Illustration: _Emilio Segrè_]
[Illustration: _Edwin M. McMillan_]
[Illustration: _Otto R. Frisch_]
[Illustration: _Glenn T. Seaborg_]
[Illustration: _Philip H. Abelson_]
What happened was exactly what was expected. Uranium-238 (92 protons,
146 neutrons) added a neutron to become uranium-239 (92 protons, 147
neutrons), which emitted a beta particle to become neptunium-239 (93
protons, 146 neutrons).
In fact, neptunium-239 also emitted a beta particle so it ought to
become an isotope of an element even higher in the atomic number scale.
This one, element 94, was named “plutonium” after Pluto, the planet
beyond Neptune. The isotope, plutonium-239, formed from neptunium-239,
was only feebly radioactive, however, and it was not clearly identified
until 1941.
The actual discovery of the element plutonium came the year before,
however, when neptunium-238 was formed. It emitted a beta particle and
became plutonium-238, an isotope that was radioactive enough to be
easily detected and identified by Glenn Theodore Seaborg (1912- ),
and his co-workers, who completed McMillan’s experiments when he was
called away to other defense research.
Neptunium and plutonium were the first “transuranium elements” to be
produced in the laboratory, but they weren’t the last. Over the next 30
years, isotopes were formed that contained more and more protons in the
nucleus and therefore had higher and higher atomic numbers. At the
moment of writing, isotopes of every element up to and including element
105 have been formed.
A number of these new elements have been named for some of the
scientists important in the history of nuclear research. Element 96 is
“curium”, named for Pierre and Marie Curie; element 99 is “einsteinium”
for Albert Einstein; and element 100 is “fermium” for Enrico Fermi.
Element 101 is “mendelevium” for the Russian chemist Dmitri Mendeléev,
who early in 1869 was the first to arrange the elements in a reasonable
and useful order. Element 103 is “lawrencium” for Ernest O. Lawrence.
“Rutherfordium” for Ernest Rutherford has been proposed for element 104.
And “hahnium” for Otto Hahn (1879-1968), a German physical chemist whose
contribution we will come to shortly, has been proposed for element 105.
Neptunium, however, was not the first new element to be created in the
laboratory. In the early 1930s, there were still 2 elements with fairly
low atomic numbers that had never been discovered. These were the
elements with atomic numbers 43 and 61.
In 1937, though, molybdenum (atomic number 42) had been bombarded with
neutrons in Lawrence’s laboratory in the United States. It might contain
small quantities of element 43 as a result. The Italian physicist Emilio
Segrè (1905- ), who had worked with Fermi, obtained a sample of the
bombarded molybdenum and indeed obtained indications of the presence of
element 43. It was the first new element to be manufactured by
artificial means and was called “technetium” from the Greek word for
“artificial”.
The technetium isotope that was formed was radioactive. Indeed, all the
technetium isotopes are radioactive. Element 61, discovered in 1945 and
named “promethium”, also has no stable isotopes. Technetium and
promethium are the only elements with atomic numbers less than 84 that
do not have even a single stable isotope.
The Discovery of Fission
But let us get back to the bombardment of uranium with neutrons research
that Fermi had begun. After he had reported his work, other physicists
repeated it and also got a variety of beta particles and were also
unable to decide what was going on.
[Illustration: _Lise Meitner and Otto Hahn in their laboratory in the
1930s._]
One way to tackle the problem was to add to the system some stable
element that was chemically similar to the tiny traces of radioactive
isotopes that might be produced through the bombardment of uranium.
Afterwards the stable element could probably be separated out of the
mixture and the trace of radioactivity would, it was hoped, be carried
along with it. The stable element would be a “carrier”.
Among those working on the problem were Otto Hahn and his Austrian
co-worker, the physicist Lise Meitner (1878-1968). Among the potential
carriers they added to the system was the element, barium, which has an
atomic number of 56. They found that a considerable quantity of the
radioactivity did indeed accompany the barium when they separated that
element out of the system.
A natural conclusion was that the isotopes producing the radioactivity
belonged to an element that was chemically very similar to barium.
Suspicion fell at once on radium (atomic number 88), which was very like
barium indeed as far as chemical properties were concerned.
Lise Meitner, who was Jewish, found it difficult to work in Germany,
however, for it was then under the rule of the strongly anti-Semitic
Nazi regime. In March 1938 Germany occupied Austria, which became part
of the German realm. Meitner was no longer protected by her Austrian
citizenship and had to flee the country and go to Stockholm, Sweden.
Hahn remained in Germany and continued working on the problem with the
German physical chemist Fritz Strassman (1902- ).
Although the supposed radium, which possessed the radioactivity, was
very like barium in chemical properties, the two were not entirely
identical. There were ways of separating them, and Hahn and Strassman
busied themselves in trying to accomplish this in order to isolate the
radioactive isotopes, concentrate them, and study them in detail. Over
and over again, however, they failed to separate the barium and the
supposed radium.
Slowly, it began to seem to Hahn that the failure to separate the barium
and the radioactivity meant that the isotopes to which the radioactivity
belonged had to be so much like barium as to be nothing else _but_
barium. He hesitated to say so, however, because it seemed unbelievable.
If the radioactive isotopes included radium, that was conceivable.
Radium had an atomic number of 88, only four less than uranium’s 92. You
could imagine that a neutron being absorbed by a uranium nucleus might
make the latter so unstable as to cause it to emit 2 alpha particles and
become radium. Barium, however, had an atomic number of 56, only a
little over half that of uranium. How could a uranium nucleus be made to
turn into a barium nucleus unless it more or less broke in half? Nothing
like that had ever been observed before and Hahn hesitated to suggest
it.
While he was nerving himself to do so, however, Lise Meitner, in
Stockholm, receiving reports of what was being done in Hahn’s laboratory
and thinking about it, decided that unheard-of or not, there was only
one explanation. The uranium nucleus _was_ breaking in half.
Actually, when one stopped to think of it (after getting over the
initial shock) it wasn’t so unbelievable at that. The nuclear force is
so short-range, it barely reaches from end to end of a large nucleus
like that of uranium. Left to itself, it holds together most of the
time, but with the added energy of an entering neutron, we might imagine
shock waves going through it and turning the nucleus into something like
a quivering drop of liquid. Sometimes the uranium nucleus recovers,
keeps the neutron, and then goes on to beta-particle emission. And
sometimes the nucleus stretches to the point where the nuclear force
doesn’t quite hold it together. It becomes a dumbbell shape and then the
electromagnetic repulsion of the two halves (both positively charged)
breaks it apart altogether.
It doesn’t break into equal halves. Nor does it always break at exactly
the same place, so that there were a number of different fragments
possible (which was why there was so much confusion). Still, one of the
more common ways in which it might break would be into barium and
krypton. (Their respective atomic numbers, 56 and 36, would add up to
92.)
Meitner and her nephew, Otto Robert Frisch (1904- ), who was in
Copenhagen, Denmark, prepared a paper suggesting that this was what was
happening. It was published in January 1939. Frisch passed it on to the
Danish physicist Niels Bohr (1885-1962) with whom he was working. The
American biologist William Archibald Arnold (1904- ), who was also
working in Copenhagen at the time, suggested that the splitting of the
uranium nucleus into halves be called “fission”, the term used for the
division-in-two of living cells. The name stuck.
In January 1939, just about the time Meitner and Frisch’s paper was
published, Bohr had arrived in the United States to attend a conference
of physicists. He carried the news of fission with him. The other
physicists attending the conference heard the news and in a high state
of excitement at once set about studying the problem. Within a matter of
weeks, the fact of uranium fission was confirmed over and over.
One striking fact about uranium fission was the large amount of energy
it released. In general, when a very massive nucleus is converted to a
less massive one, energy is released because of the change in the mass
defect, as Aston had shown in the 1920s. When the uranium nucleus breaks
down through the ordinary radioactive processes to become a less massive
lead nucleus, energy is given off accordingly. When, however, it breaks
in two to become the much less massive nuclei of barium and krypton (or
others in that neighborhood) much more energy is given off.
It quickly turned out that uranium fission gave off something like ten
times as much nuclear energy per nucleus than did any other nuclear
reaction known at the time.
Even so, the quantity of energy released by uranium fission was only a
tiny fraction of the energy that went into the preparation of the
neutrons used to bring about the fission, if each neutron that struck a
uranium atom brought about a single fission of that 1 atom.
Under those conditions, Rutherford’s suspicion that mankind would never
be able to tap nuclear energy probably still remained true. (He had been
dead for 2 years at the time of the discovery of fission.)
However, those were not the conditions.
The Nuclear Chain Reaction
Earlier in this history, we discussed chain reactions involving chemical
energy. A small bit of energy can ignite a chemical reaction that would
produce more than enough energy to ignite a neighboring section of the
system, which would in turn produce still more—and so on, and so on. In
this way the flame of a single match could start a fire in a leaf that
would burn down an entire forest, and the energy given off by the
burning forest would be enormously higher than the initial energy of the
match flame.
Might there not be such a thing as a “nuclear chain reaction”? Could one
initiate a nuclear reaction that would produce something that would
initiate more of the same that would produce something that would
initiate still more of the same and so on?
In that case, a nuclear reaction, once started, would continue of its
own accord, and in return for the trifling investment that would serve
to start it—a single neutron, perhaps—a vast amount of breakdowns would
result with the delivery of a vast amount of energy. Even if it were
necessary to expend quite a bit of energy to produce the 1 neutron that
would start the chain reaction, one would end with an enormous profit.
What’s more, since the nuclear reaction would spread from nucleus to
nucleus with millionths-of-a-second intervals, there would be, in a very
brief time, so many nuclei breaking down that there would be a vast
explosion. The explosion was sure to be millions of times as powerful as
ordinary chemical explosions involving the same quantity of exploding
material, since the latter used only the electromagnetic interaction,
while the former used the much stronger nuclear interaction.
The first to think seriously of such a nuclear chain reaction was the
Hungarian physicist Leo Szilard (1898-1964). He was working in Germany
in 1933 when Adolf Hitler came to power and, since he was Jewish, he
felt it would be wise to leave Germany. He went to Great Britain and
there, in 1934, he considered certain new types of nuclear reactions
that had been discovered.
In these, it sometimes happened that a fast neutron might strike a
nucleus with sufficient energy to cause it to emit 2 neutrons. In that
way the nucleus, absorbing 1 neutron and emitting 2, would become a
lighter isotope of the same element.
But what would happen if each of the 2 neutrons that emerged from the
original target nucleus struck new nuclei and forced the emission of a
pair of neutrons from each. There would now be a total of 4 neutrons
flying about and if each struck new nuclei there would next be 8
neutrons and so on. From the initial investment of a single neutron
there might soon be countless billions initiating nuclear reactions.
Szilard, fearing the inevitability of war and fearing further that the
brutal leaders of Germany might seek and use such a nuclear chain
reaction as a weapon in warfare, secretly applied for a patent on a
device intending to make use of such a nuclear chain reaction. He hoped
to turn it over to the British Government, which might then use its
possession as a way of restraining the Nazis and keeping the peace.
However, it wouldn’t have worked. It took the impact of a very energetic
neutron to bring about the emission of 2 neutrons. The neutrons that
then emerged from the nucleus simply didn’t have enough energy to keep
things going. (It was like trying to make wet wood catch fire.)
But what about uranium fission? Uranium fission was initiated by slow
neutrons. What if uranium fission also produced neutrons as well as
being initiated by a neutron? Would not the neutrons produced serve to
initiate new fissions that would produce new neutrons and so on
endlessly?
It seemed very likely that fission produced neutrons and indeed, Fermi,
at the conference where fission was first discussed, suggested it at
once. Massive nuclei possessed more neutrons per proton than less
massive ones did. If a massive nucleus was broken up into 2 considerably
less massive ones, there would be a surplus of neutrons. Suppose, for
instance, uranium-238 broke down into barium-138 and krypton-86.
Barium-138 contains 82 neutrons and krypton-86 50 neutrons for a total
of 132. The uranium-238 nucleus, however, contains 146 neutrons.
The uranium fission process was studied at once to see if neutrons were
actually given off and a number of different physicists, including
Szilard, found that they were.
Now Szilard was faced with a nuclear chain reaction he was certain would
work. Only slow neutrons were involved and the individual nuclear
breakdowns were far more energetic than anything else that had yet been
discovered. If a chain reaction could be started in a sizable piece of
uranium, unimaginable quantities of energy would be produced. Just 1
gram of uranium, undergoing complete fission, would deliver the energy
derived from the total burning of 3 tons of coal and would deliver that
energy in a tiny fraction of a second.
Szilard, who had come to the United States in 1937, clearly visualized
the tremendous explosive force of something that would have to be called
a “nuclear bomb”. Szilard dreaded the possibility that Hitler might
obtain the use of such a bomb through the agency of Germany’s nuclear
scientists.
Partly through Szilard’s efforts, physicists in the United States and in
other Western nations opposed to Hitler began a program of voluntary
secrecy in 1940, to avoid passing along any hints to Germany. What’s
more, Szilard enlisted the services of two other Hungarian refugees, the
physicists Eugene Paul Wigner (1902- ) and Edward Teller (1908- )
and all approached Einstein, who had also fled Germany and come to
America.
[Illustration: _Leo Szilard_]
[Illustration: _Eugene P. Wigner_]
Einstein was the most prestigious scientist then living and it was
thought a letter from him to the President of the United States would be
most persuasive. Einstein signed such a letter, which explained the
possibility of a nuclear bomb and urged that the United States not allow
a potential enemy to come into possession of it first.
Largely as a result of this letter, a huge research team was put
together in the United States, to which other Western nations also
contributed, with but one aim—to develop the nuclear bomb.
The Nuclear Bomb
Although the theory of the nuclear bomb seemed clear and simple, a great
many practical difficulties stood in the way. In the first place, if
only uranium atoms underwent fission a supply of uranium had at least to
be obtained in pure form, for if the neutrons struck nuclei of elements
other than uranium, they would simply be absorbed and removed from the
system, ending the possibility of a chain reaction. This alone was a
heavy task, since there had been so little use for uranium in quantity
that there was almost no supply in existence and no experience in how to
purify it.
Secondly, the supply of uranium might have to be a large one, for
neutrons didn’t necessarily enter the first uranium atom they
approached. They moved about here and there, making glancing collisions,
and travelling quite a distance, perhaps, before striking head-on and
entering a nucleus. If in that time they had passed outside the lump of
uranium, they were useless.
[Illustration: Franklin D. Roosevelt]
Albert Einstein
Old Grove Rd.
Nassau Point
Peconic, Long Island
August 2nd, 1939
F.D. Roosevelt,
President of the United States,
White House
Washington, D.C.
Sir:
Some recent work by E. Fermi and L. Szilard, which has been communicated
to me in manuscript, leads me to expect that the element uranium may be
turned into a new and important source of energy in the immediate
future. Certain aspects of the situation which has arisen seem to call
for watchfulness and, if necessary, quick action on the part of the
Administration. I believe therefore that it is my duty to bring to your
attention the following facts and recommendations:
In the course of the last four months it has been made probable—through
the work of Joliot in France as well as Fermi and Szilard in
America—that it may become possible to set up a nuclear chain reaction
in a large mass of uranium, by which vast amounts of power and large
quantities of new radium-like elements would be generated. Now it
appears almost certain that this could be achieved in the immediate
future.
This new phenomenon would also lead to the construction of bombs, and it
is conceivable—though much less certain—that extremely powerful bombs of
a new type may thus be constructed. A single bomb of this type, carried
by boat and exploded in a port, might very well destroy the whole port
together with some of the surrounding territory. However, such bombs
might very well prove to be too heavy for transportation by air.
[Illustration: _Albert Einstein_]
The United States has only very poor ores of uranium in moderate
quantities. There is some good ore in Canada and the former
Czechoslovakia, while the most important source of uranium is Belgian
Congo.
In view of this situation you may think it desirable to have some
permanent contact maintained between the Administration and the group
of physicists working on chain reactions in America. One possible way
of achieving this might be for you to entrust with this task a person
who has your confidence and who could perhaps serve in an inofficial
capacity. His task might comprise the following:
a) to approach Government Departments, keep them informed of the
further development, and put forward recommendations for Government
action, giving particular attention to the problem of securing a
supply of uranium ore for the United States;
b) to speed up the experimental work, which is at present being
carried on within the limits of the budgets of University
laboratories, by providing funds, if such funds be required, through
his contacts with private persons who are willing to make
contributions for this cause, and perhaps also by obtaining the
co-operation of industrial laboratories which have the necessary
equipment.
I understand that Germany has actually stopped the sale of uranium
from the Czechoslovakian mines which she has taken over. That she
should have taken such early action might perhaps be understood on the
ground that the son of the German Under-Secretary of State, von
Weizsäcker, is attached to the Kaiser-Wilhelm-Institut in Berlin where
some of the American work on uranium is now being repeated.
Yours very truly,
[Illustration: /signed/]
(Albert Einstein)
As the quantity of uranium within which the fission chain reaction was
initiated grew larger, more and more of the neutrons produced found a
mark and the fission reaction would die out more and more slowly.
Finally, at some particular size—the “critical size”—the fission
reaction did not die at all, but maintained itself, with enough of the
neutrons produced finding their mark to keep the nuclear reaction
proceeding at a steady rate. At any greater size the nuclear reaction
would accelerate and there would be an explosion.
It wasn’t even necessary to send neutrons into the uranium to start the
process. In 1941 the Russian physicist Georgii Nikolaevich Flerov
(1913- ) found that every once in a while a uranium atom would
undergo fission without the introduction of a neutron. Occasionally the
random quivering of a nucleus would bring about a shape that the nuclear
interaction could not bring back to normal and the nucleus would then
break apart. In a gram of ordinary uranium, there is a nucleus
undergoing such “spontaneous fission” every 2 minutes on the average.
Therefore, enough uranium need only be brought together to surpass
critical size and it will explode within seconds, for the first nucleus
that undergoes spontaneous fission will start the chain reaction.
First estimates made it seem that the quantity of uranium needed to
reach critical size was extraordinarily great. Fully 99.3% of the metal
is uranium-238, however, and, as soon as fission was discovered, Bohr
pointed out that there were theoretical reasons for supposing that it
was the uranium-235 isotope (making up only 0.7% of the whole) that was
the one undergoing fission. Investigation proved him right. Indeed, the
uranium-238 nucleus tended to absorb slow neutrons without fission, and
to go on to beta-particle production that formed isotopes of neptunium
and plutonium. In this way uranium-238 actually interfered with the
chain reaction.
In any quantity of uranium, the more uranium-235 present and the less
uranium-238, the more easily the chain reaction would proceed and the
lower the critical size needed. Vast efforts were therefore made to
separate the 2 isotopes and prepare uranium with a higher than normal
concentration of uranium-235 (“enriched uranium”).
Of course, there was no great desire for a fearful explosion to get out
of hand while the chain reaction was being studied. Before any bomb
could be constructed, the mechanism of the chain reaction would have to
be studied. Could a chain reaction capable of producing energy (for
useful purposes as well as for bombs) be established? To test this, a
quantity of uranium was gathered in the hope that a _controlled_ chain
reaction of uranium fission could be established. For that purpose,
control rods of a substance that would easily absorb neutrons and slow
the chain reaction were used. The metal, cadmium, served admirably for
this purpose.
Then, too, the neutrons released by fission were pretty energetic. They
tended to travel too far too soon and get outside the lump of uranium
too easily. To produce a chain reaction that could be studied with some
safety, the presence of a moderator was needed. This was a supply of
small nuclei that did not absorb neutrons readily, but absorbed some of
the energy of collision and slowed down any neutron that struck it.
Nuclei such as hydrogen-2, beryllium-9, or carbon-12 were useful
moderators. When the neutrons produced by fission were slowed, they
travelled a smaller distance before being absorbed in their turn and the
critical size would again be reduced.
Toward the end of 1942 the initial stage of the project reached a
climax. Blocks of graphite containing uranium metal and uranium oxide
were piled up in huge quantities (enriched uranium was not yet
available) in order to approach critical size. This took place under the
stands of a football stadium at the University of Chicago, with Enrico
Fermi (who had come to the United States in 1938) in charge.[1]
The large structure was called an “atomic pile” at first because of the
blocks of graphite being piled up. The proper name for such a device,
and the one that was eventually adopted, was, however, “nuclear
reactor”.
On December 2, 1942, calculations showed that the nuclear reactor was
large enough to have reached critical size. The only thing preventing
the chain reaction from sustaining itself was the cadmium rods that were
inserted here and there in the pile and that were soaking up neutrons.
[Illustration: _Cutaway model of the West Stands of Stagg Field showing
the first pile in the squash court beneath it._]
[Illustration: _The exterior of the building._]
[Illustration: _Graphite layers form the base of the pile, left. On the
right is the seventh layer of graphite and edges of the sixth layer
containing 3¼-inch pseudospheres of black uranium oxide. Beginning with
layer 6, alternate courses of graphite containing uranium metal and/or
uranium oxide fuel were separated by layers of solid graphite blocks._]
[Illustration: _Tenth layer of graphite blocks containing pseudospheres
of black and brown uranium oxide. The brown briquets, slightly richer in
uranium, were concentrated in the central area. On the right is the
nineteenth layer of graphite covering layer 18 containing slugs of
uranium oxide._]
One by one the cadmium rods were pulled out. The number of uranium atoms
undergoing fission each second rose and, finally, at 3:45 p.m., the
uranium fission became self-sustaining. It kept going on its own (with
the cadmium rods ready to be pushed in if it looked as though it were
getting out of hand—something calculations showed was not likely).
News of this success was announced to Washington by a cautious telephone
call from Arthur Holly Compton (1892-1962) to James Bryant Conant
(1893- ). “The Italian navigator has landed in the new world”, said
Compton. Conant asked, “How were the natives?”, and the answer was,
“Very friendly”.
This was the day and moment when the world entered the “nuclear age”.
For the first time, mankind had constructed a device in which the
nuclear energy being given off was greater than the energy poured in.
Mankind had tapped the reservoirs of nuclear energy and could put it to
use. Had Rutherford lived but 6 more years, he would have seen how wrong
he was to think it could never be done.
The people of earth remained unaware of what had taken place in Chicago
and physicists continued to work toward the development of the nuclear
bomb.
Enriched uranium was successfully prepared. Critical sizes were brought
low enough to make a nuclear bomb small enough to be carried by plane to
some target. Suppose one had 2 slabs of enriched uranium, each below
critical size, but which were above critical size if combined. And
suppose an explosive device were added that, at some desired moment,
could be set off in such a way that it would drive 1 slab of enriched
uranium against the other. There would be an instant explosion of
devastating power. Or suppose the enriched uranium were arranged in
loosely packed pieces to begin with so that the flying neutrons were in
open air too often to maintain the chain reaction. A properly arranged
explosion might compress the uranium into a dense ball. Neutron
absorption would become more efficient and again, an explosion would
follow.
[Illustration: _Nuclear Fission of Uranium: A neutron hits the nucleus
of an atom of uranium. The neutron splits the nucleus into two parts and
creates huge amounts of energy in the form of heat. At the same time
other neutrons are released from the splitting nucleus and these
continue the fission process in a chain reaction._]
On July 16, 1945, a device that would result in a nuclear explosion was
set up near Alamogordo, New Mexico, with nervous physicists watching
from a safe distance. It worked perfectly; the explosion was tremendous.
By that time Nazi Germany had been defeated, but Japan was still
fighting. Two more devices were prepared. After a warning, one was
exploded over the Japanese city of Hiroshima on August 6, 1945, and the
other over Nagasaki 2 days later. The Japanese government surrendered
and World War II came to an end.
It was with the blast over Hiroshima that the world came to know it was
in the nuclear age and that the ferocious weapon of the nuclear bomb
existed. (The popular name for it at the time was “atomic bomb” or
“A-bomb”.)
During the war, German scientists may have been trying to develop a
nuclear bomb, but, if so, they had not yet succeeded at the time Germany
met its final defeat. Soviet physicists, under Igor Vasilievich
Kurchatov (1903-1960), were also working on the problem. The dislocation
of the war, which inflicted much more damage on the Soviet Union than on
the United States, kept the Soviet effort from succeeding while it was
on. However, since the Soviets were among the victors, they were able to
continue after the war.
In 1949 the Soviets exploded their first nuclear bomb. In 1952 the
British did the same; in 1960, the French; and in 1964, the Chinese.
Although many nuclear bombs have been exploded for test purposes, the
two over Hiroshima and Nagasaki have been the only ones used in time of
war.
Nor need nuclear bombs be considered as having destructive potential
only. There is the possibility that, with proper precautions, they might
be used to make excavations, blast out harbors or canals, break up
underground rock formations to recover oil or other resources, and in
other ways do the work of chemical explosives with far greater speed and
economy. It has even been suggested that a series of nuclear bomb
explosions might be used to hurl space vehicles forward in voyages away
from earth.
Nuclear Reactors
The development of the nuclear chain reaction was not in the direction
of bombs only. Nuclear reactors designed for the controlled production
of useful energy multiplied in number and in efficiency since Fermi’s
first “pile”. Many nations now possess them, and they are used for a
variety of purposes.[2]
[Illustration: _The USS_ Nautilus, _the world’s first nuclear powered
submarine, in New York harbor_.]
In 1954 the first nuclear submarine the USS _Nautilus_ was launched by
the United States. Its power was obtained entirely from a nuclear
reactor, and it was not necessary for it to rise to the surface at short
intervals in order to recharge its batteries. Nuclear submarines have
crossed the Arctic Ocean under the ice cover, and have circumnavigated
the globe without surfacing.
In 1959 both the Soviet Union and the United States launched
nuclear-powered surface vessels. The Soviet ship was the icebreaker,
_Lenin_, and the American ship was a merchant vessel, the NS _Savannah_.
In the 1950s nuclear reactors were also used as the source of power for
the production of electricity for civilian use. The Soviet Union built a
small station of this sort in 1954, which had a capacity of 5,000
kilowatts. The British built one of 92,000 kilowatt capacity, which they
called Calder Hall. The first American nuclear reactor for civilian use
began operation at Shippingport, Pennsylvania, in 1958. It was the first
really full-scale civilian nuclear power plant in the world.
The world appeared to have far greater sources of energy than had been
expected. The “fossil fuels”—coal, oil and natural gas—were being used
at such a rate that many speculated that the gas and oil would be gone
in decades and the coal in centuries. Was it possible that uranium might
now serve as a new source that would last indefinitely?
It was rather disappointing that it was uranium-235 which underwent
fission, because that isotope made up only 0.7% of the uranium that
existed. If uranium-235 were all we had and all we ever could have, the
energy supply of the world would still be rather too limited.
There were other possible “nuclear fuels”, however. There was
plutonium-239, which would also fission under neutron bombardment. It
had an ordinary half-life (for a radioactive change in which it gave off
alpha particles) of 24,300 years, which is long enough to make it easy
to handle.
But how can plutonium-239 be formed in sufficient quantities to be
useful? After all, it doesn’t occur in nature. Surprisingly, that turned
out to be easy. Uranium-238 atoms will absorb many of the neutrons that
are constantly leaking out of the reactor and will become first
neptunium-239 and then plutonium-239. The plutonium, being a different
element from the uranium, can be separated from uranium and obtained in
useful quantities.
Such a device is called a “breeder reactor” because it breeds fuel.
Indeed, it can be so designed to produce more plutonium-239 than the
uranium-235 it uses up, so that you actually end up with more nuclear
fuel than you started with. In this way, all the uranium on earth (and
not just uranium-235) can be considered potential nuclear fuel.
[Illustration: _The Shippingport Atomic Power Station, the first
full-scale, nuclear-electric station built exclusively for civilian
needs, provides electricity for the homes and factories of the greater
Pittsburgh area. The pressurized-water reactor, which now has a
90,000-net-electrical-kilowatt capacity, began commercial operation in
1957. The reactor is in the large building in the center._]
[Illustration: _The lights of downtown Pittsburgh._]
The first breeder reactor was completed at Arco, Idaho, in August 1951,
and on December 20 produced the very first electricity on earth to come
from nuclear power. Nevertheless, breeder reactors for commercial use
are still a matter for the future.[3]
Another isotope capable of fissioning under neutron bombardment is
uranium-233. It does not occur in nature, but was formed in the
laboratory by Seaborg and others in 1942. It has a half-life of 162,000
years. It can be formed from naturally occurring thorium-232.
Thorium-232 will absorb a neutron to become thorium-233. Then 2 beta
particles are given off so that the thorium-233 becomes first
protactinium-233 and then uranium-233.
If a thorium shell surrounds a nuclear reactor, fissionable uranium-233
is formed within it and is easily separated from the thorium. In this
way, thorium is also added to the list of earth’s potential nuclear
fuels.[4]
If all the uranium and thorium in the earth’s crust (including the thin
scattering of those elements through granite, for instance) were
available for use, we might get up to 100 times as much energy from it
as from all the coal and oil on the planet. Unfortunately, it is very
unlikely that we will ever be able to make use of all the uranium and
thorium. It is widely and thinly spread through the crustal rocks and
much of it could not be extracted without using up more energy than
would be supplied by it once isolated.
Another problem rests with the nature of the fission reaction. When the
uranium-235 nucleus (or plutonium-239 or uranium-233) undergoes fission,
it breaks up into any of a large number of middle-sized nuclei that are
radioactive—much more intensely radioactive than the original fuel. (It
was from among these “fission products” that isotopes of element 61 were
first obtained in 1945. Coming from the nuclear fire, it reminded its
discoverers of Prometheus, who stole fire from the sun in the Greek
myths, and so it was called “promethium”.)
The fission products still contain energy and some of them can be used
in lightweight “nuclear batteries”. Such nuclear batteries were first
built in 1954. Some batteries, using plutonium-238 rather than fission
products, have been put to use in powering artificial satellites over
long periods.
Unfortunately, only a small proportion of the fission products can be
put to profitable use. Most must be disposed of. They are dangerous
because the radiations they give off are deadly and cannot be detected
by the ordinary senses. They are very difficult to dispose of safely,
and they must not be allowed to get into the environment, especially
since some of them remain dangerous for decades or even centuries.
[Illustration: _The Experimental Breeder Reactor No. 2 building complex
in Idaho. The reactor is in the dome-shaped structure._]
NUCLEAR FUSION
The Energy of the Sun
As it happens, though, nuclear fission is not the only route to useful
nuclear energy.
Aston’s studies in the 1920s had shown that it was the middle-sized
nuclei that were most tightly packed. Energy would be given off if
middle-sized nuclei were produced from either extreme. Not only would
energy be formed by the breakup of particularly massive nuclei through
fission, but also through the combination of small nuclei to form larger
ones (“nuclear fusion”).
In fact, from Aston’s studies it could be seen that, mass for mass,
nuclear fusion would produce far more energy than nuclear fission. This
was particularly true in the conversion of hydrogen to helium; that is,
the conversion of the individual protons of 4 separate hydrogen nuclei
into the 2-proton—2-neutron structure of the helium nucleus. A gram of
hydrogen, undergoing fusion to helium, would deliver some fifteen times
as much energy as a gram of uranium undergoing fission.
As early as 1920, the English astronomer Arthur Stanley Eddington
(1882-1944) had speculated that the sun’s energy might be derived from
the interaction of subatomic particles. Some sort of nuclear reaction
seemed, by then, to be the most reasonable way of accounting for the
vast energies constantly being produced by the sun.
The speculation became more plausible with each year. Eddington himself
studied the structure of stars, and by 1926 had produced convincing
theoretical reasons for supposing that the center of the sun was at
enormous densities and temperatures. A temperature of some 15,000,000 to
20,000,000°C seemed to characterize the sun’s center.
At such temperatures, atoms could not exist in earthly fashion. Held
together by the sun’s strong gravitational field, they collided with
such energy that all or almost all their electrons were stripped off,
and little more than bare nuclei were left. These bare nuclei could
approach each other much more closely than whole atoms could (which was
why the center of the sun was so much more dense than earthly matter
could be). The bare nuclei, smashing together at central-sun
temperatures, could cling together and form more complex nuclei. Nuclear
reactions brought about by such intense heat (millions of degrees) are
called “thermonuclear reactions”.
As the 1920s progressed further studies of the chemical structure of the
sun showed it to be even richer in hydrogen than had been thought. In
1929 the American astronomer Henry Norris Russell (1877-1957) reported
evidence that the sun was 60% hydrogen in volume. (Even this was too
conservative; 80% is considered more nearly correct now.) If the sun’s
energy were based on nuclear reactions at all, then it had to be the
result of hydrogen fusion. Nothing else was present in sufficient
quantity to be useful as a fuel.
More and more was learned about the exact manner in which nuclei
interacted and about the quantity of energy given off in particular
nuclear reactions. It became possible to calculate what might be going
on inside the sun by considering the densities and temperatures present,
the kind and number of different nuclei available, and the quantity of
energy that must be produced. In 1938 the German-American physicist Hans
Albrecht Bethe (1906- ) and the German astronomer Carl Friedrich von
Weizsäcker (1912- ) independently worked out the possible reactions,
and hydrogen fusion was shown to be a thoroughly practical way of
keeping the sun going.
Thanks to the high rate of energy production by thermonuclear reactions
and to the vast quantity of hydrogen in the sun, not only has it been
possible for the sun to have been radiating energy for the last
5,000,000,000 years or so, but it will continue to radiate energy in the
present fashion for at least 5,000,000,000 years into the future.
[Illustration: _Hans Bethe_]
Even so, the sheer quantity of what is going on in the sun is staggering
in earthly terms. In the sun 650,000,000 tons of hydrogen are converted
into helium every second, and in the process each second sees the
disappearance of 4,600,000 tons of mass.
Thermonuclear Bombs
Could thermonuclear reactions be made to take place on earth? The
conditions that exist in the center of the sun would be extremely
difficult to duplicate on the earth, so there was a natural search for
any kind of nuclear fusion that would produce similar energies to those
going on in the sun but which would be easier to bring about.
There are 3 hydrogen isotopes known to exist. Ordinary hydrogen is
almost entirely hydrogen-1, with a nucleus made up of a single proton.
Small quantities of hydrogen-2 (deuterium) with a nucleus made up of a
proton plus a neutron also exist and such atoms are perfectly stable.
In 1934 Rutherford, along with the Australian physicist Marcus Laurence
Elwin Oliphant (1901- ) and the Austrian chemist Paul Harteck
(1902- ) sent hydrogen-2 nuclei flying into hydrogen-2 targets and
formed hydrogen-3 (also called “tritium” from the Greek word for
“third”) with a nucleus made up of a proton plus 2 neutrons. Hydrogen-3
is mildly radioactive.
Hydrogen-2 fuses to helium more easily than hydrogen-1 does and, all
things being equal, hydrogen-2 will do so at lower temperatures than
hydrogen-1. Hydrogen-3 requires lower temperatures still. But even for
hydrogen-3 it still takes millions of degrees.
Hydrogen-3, although the easiest to be forced to undergo fusion, exists
only in tiny quantities.
Hydrogen-2, therefore, is the one to pin hopes on especially in
conjunction with hydrogen-3. Only 1 atom out of every 6000 hydrogen
atoms is hydrogen-2, but that is enough. There exists a vast ocean on
earth that is made up almost entirely of water molecules and in each
water molecule 2 hydrogen atoms are present. Even if only 1 in 6000 of
these hydrogen atoms is deuterium that still means there are about
35,000 billion tons of deuterium in the ocean.
What’s more, it isn’t necessary to dig for that deuterium or to drill
for it. If ocean water is allowed to run through separation plants, the
deuterium can be extracted without very much trouble. In fact, for the
energy you could get out of it, deuterium from the oceans, extracted by
present methods and without allowing for future improvement, would be
only one-hundredth as expensive as coal.
The deuterium in the world’s ocean, if allowed to undergo fusion little
by little, would supply mankind with enough energy to keep us going at
the present rate for 500,000,000,000 years. To be sure, to make
deuterium fusion practical, it may be necessary to make use of rarer
substances such as the light metal lithium. This will place a sharper
limit on the energy supply but even if we are careful, fusion would
probably supply mankind with energy for as long as mankind will exist.
Then, too, there would seem to be no danger of hydrogen fusion plants
running out of control. Only small quantities of deuterium would be in
the process of fusion at any one time. If anything at all went wrong,
the deuterium supply could be automatically cut off and the fusion
process, with so little involved, would then stop instantly. Moreover,
there would be less reason to worry about atomic wastes, for the most
dangerous products—hydrogen-3 and neutrons—could be easily taken care
of.
It seems ideal, but there is a catch. However clear the theory, before a
fusion power station can be established some practical method must be
found to start the fusion process, which means finding some way for
attaining temperatures in the millions of degrees.
One method for obtaining the necessary temperature was known by 1945. An
exploding fission bomb would do it. If, somehow, the necessary
hydrogen-2 was combined with a fission bomb, the explosion would set off
a fusion reaction that would greatly multiply the energy released. You
would have in effect a “thermonuclear bomb”. (To the general public,
this was commonly known as a “hydrogen bomb” or an “H-bomb”.)
In 1952 the first fusion device was exploded by the United States in the
Marshall Islands. Within months, the Soviet Union had exploded one of
its own and in time thermonuclear bombs thousands of times as powerful
as the first fission bomb over Hiroshima were built and exploded.
All thermonuclear bombs have been exploded only for test purposes. Even
testing seems to be dangerous, however, at least if it is carried on in
the open atmosphere. The radioactivity liberated spreads over the world
and may do slow but cumulative damage.
Controlled Fusion
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
struggle to overcome class barriers in 19th century England—is well
presented. Quotations from letters, diaries, and published works give
a clear picture of Dalton’s atomic theory research and his time.
_Man-made Transuranium Elements_, Glenn T. Seaborg, Prentice Hall,
Inc., Englewood Cliffs, New Jersey, 1963, 120 pp., $6.95 (hardback);
$2.95 (paperback). The discovery, properties, and applications of
elements heavier than uranium are considered in this book, which is
designed as an introduction to the subject. Glenn Seaborg was
co-discoverer of nine of the twelve transuranium elements.
_The Nature of Matter: Physical Theory from Thales to Fermi_, Ginestra
Amaldi, translated by Peter Astbury, Chicago University Press,
Chicago, Illinois, 1966, 332 pp., $5.95. A nontechnical history of
atomic energy.
_Niels Bohr: His Life and Work as Seen by His Friends and Colleagues_,
S. Rozental (Editor), John Wiley and Sons, Inc., New York, 1967, 355
pp., $5.95. An articulate and scholarly biography by the friends and
co-workers of this outstanding atomic pioneer.
_Niels Bohr: The Man, His Science, and the World They Changed_, Ruth
Moore, Alfred A. Knopf, Inc., New York, 1966, 436 pp., $7.95. An
interesting biography of one of the pioneers in the study of the
internal structure of the atom.
_Otto Hahn: My Life_, Otto Hahn, translated by Ernest Kaiser and
Eithne Wilkins, Herder and Herder, Inc., New York, 1970, 240 pp.,
$6.50. Autobiography of the man who discovered that the atom could be
split.
_Otto Hahn: A Scientific Autobiography_, Otto Hahn, Willy Ley, editor
and translator, Charles Scribner’s Sons, New York, 1966, 320 pp.,
$9.95. Otto Hahn, winner of the 1944 Nobel Prize for his work in
atomic fission, reviews the pioneer days in which a new science was
created, and the role he played in its development.
_Physics and Beyond: Encounters and Conversations_, Werner Heisenberg,
translated by Arthur J. Pomerans, Harper and Row, Publishers, New
York, 1970, 247 pp., $7.95. Werner Heisenberg, a Nobel Prize
physicist, presents his autobiography in the form of conversations
with such men as Max Planck, Albert Einstein, Niels Bohr, Ernest
Rutherford, Otto Hahn, and Enrico Fermi.
_Physics for Poets_, Robert H. March, McGraw-Hill Book Company, New.
York, 1970, 302 pp., $7.50. A physics textbook for nonscience
students. The book covers certain developments of classical mechanics,
relativity, and atomic and quantum physics. With this book the author
won the 1971 American Institute of Physics—U. S. Steel Foundation
Science Writing Award in Physics and Astronomy.
_Sourcebook on Atomic Energy_ (third edition), Samuel Glasstone, Van
Nostrand Reinhold Company, New York, 1967, 883 pp., $15.00. An
excellent standard reference work, written for both scientists and the
general public.
_The Swift Years: The Robert Oppenheimer Story_, Peter Michelmore,
Dodd, Mead and Company, New York, 1969, 273 pp., $6.95. Oppenheimer’s
complex personality is delineated in this well-written biography. In
the bibliography is a list of books that Oppenheimer felt “had done
the most to shape his vocational attitude and philosophy of life”.
_The World of the Atom_, 2 volumes, Henry A. Boorse and Lloyd Motz
(Eds.), Basic Books, Inc., Publishers, New York, 1966, 1873 pp.,
$35.00. Contains the actual text of landmark documents in the history
of atomic physics, each preceded by commentary that places it in the
context of the discoverer’s personal life and in the conditions
prevailing in science and in society in his time.
Photo Credits
Page facing inside The “Horsehead” Nebula in Orion. Hale
cover Observatories.
Author’s Photo Jay K. Klein
Contents page Lick Observatory
116 Samuel A. Goudsmit
118 From _Atoms in the Family: My Life With Enrico
Fermi_, Laura Fermi, 1954. Copyright © by the
University of Chicago Press.
120 Top row, left, Institut fur Radium-forschung und
Kemphysik, right, Lotte Meitner-Graff, middle
row, left, Nobel Institute, right, Ernest Orlando
Lawrence Berkeley Laboratory; bottom row, right,
Ernest Orlando Lawrence Berkeley Laboratory,
left, P. H. Abelson.
123 Addison-Wesley Publishing Company
130 Top, Ike Verne; bottom, Oak Ridge National
Laboratory.
132 & 133 Letter and Roosevelt picture from the Franklin D.
Roosevelt Library; Johan Hagemeyer.
136 & 137 Argonne National Laboratory
141 U. S. Navy
143 Right, Westinghouse Electric Corporation
145 Argonne National Laboratory
152 Lick Observatory
155 Gulf Energy and Environmental Systems
156 Los Alamos Scientific Laboratory
158 Nobel Institute
159 Left, C. D. Anderson; right, Nobel Institute.
161 Ernest Orlando Lawrence Berkeley Laboratory
★ U. S. GOVERNMENT PRINTING OFFICE: 1972 - 747-189/2
The U. S. Atomic Energy Commission publishes this series of information
booklets for the general public. These booklets explain the many uses of
nuclear energy.
The booklets are listed below by subject category.
General Interest
WAS-009 Atomic Energy and Your World
WAS-002 A Bibliography of Basic Books on Atomic Energy
WAS-004 Computers
WAS-008 Electricity and Man
WAS-006 Nuclear Terms, A Glossary
WAS-013 Secrets of the Past: Nuclear Energy Applications in Art and
Archaeology
The Environment
WAS-414 Nature’s Invisible Rays
WAS-204 Nuclear Power and the Environment
Biology
WAS-102 Atoms in Agriculture
WAS-105 The Genetic Effects of Radiation
WAS-107 Radioisotopes in Medicine
WAS-109 Your Body and Radiation
Physics
WAS-401 Accelerators
WAS-403 Controlled Nuclear Fusion
WAS-404 Direct Conversion of Energy
WAS-416 Inner Space: The Structure of the Atom
WAS-406 Lasers
WAS-407 Microstructure of Matter
WAS-411 Power from Radioisotopes
Chemistry
WAS-303 The Atomic Fingerprint: Neutron Activation Analysis
WAS-302 Cryogenics, The Uncommon Cold
WAS-306 Radioisotopes in Industry
Nuclear Reactors
WAS-502 Atomic Power Safety
WAS-513 Breeder Reactors
WAS-503 The First Reactor
WAS-505 Nuclear Power Plants
WAS-507 Nuclear Reactors
WAS-508 Radioactive Wastes
Members of the general public may obtain free, single copies of six
titles of their choice. Librarians and teachers may obtain free a
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on prices and availability should be directed to:
USAEC—Technical Information Center, P. O. Box 62, Oak Ridge, TN 37830
Comments are invited regarding this booklet and others in the series.
[Illustration: UNITED STATES OF AMERICA ATOMIC ENERGY COMMISSION]
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