Title: Our Atomic World - The Story of Atomic Energy
Author: Craven, C. Jackson
Language: English
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                            OUR ATOMIC WORLD


                          by C. Jackson Craven


                       THE STORY OF ATOMIC ENERGY


                     U.S. ATOMIC ENERGY COMMISSION
                   Division of Technical Information
                    _Understanding the Atom Series_



                   The Understanding the Atom Series


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.

                                                  {Edward J. Brunenkant}
                                          Edward J. Brunenkant, Director
                                       Division of Technical Information

  UNITED STATES ATOMIC ENERGY COMMISSION

  Dr. Glenn T. Seaborg, Chairman
  James T. Ramey
  Wilfrid E. Johnson
  Dr. Theos J. Thompson
  Dr. Clarence E. Larson



                            OUR ATOMIC WORLD


                          by C. Jackson Craven



                                CONTENTS


  THE GREEKS WERE CURIOUS ABOUT MATTER                                 1
  THE ATOMIC THEORY IS CONFIRMED                                       2
  CATHODE RAYS SHOW ATOMS CONTAIN SMALLER PARTS                        3
  RADIOACTIVE ATOMS DISCOVERED                                         5
  RUTHERFORD FINDS THE ATOMIC NUCLEUS                                  6
  THE PROTON IS RECOGNIZED                                             8
  ISOTOPES ARE DISCOVERED                                              9
  THE ALCHEMISTS’ DREAM COMES TRUE                                    10
  SOME PARTICLES HAVE NO ELECTRIC CHARGE                              13
  MATTER IS ENERGY; ENERGY IS MATTER                                  14
  NUCLEI CONTAIN ENERGY                                               15
  CHRONOLOGY                                                          18
  FISSION IS EXPLAINED                                                20
  THE FISSION BOMB IS EXPLODED                                        23
  NUCLEAR ENERGY IS NEEDED FOR THE FUTURE                             25
  FUSION HAS POTENTIAL                                                26
  ISOTOPES HAVE MANY USES                                             29
  RADIOISOTOPES AT WORK                                               30
  THE ATOMIC ENERGY COMMISSION                                        31
  TOWARD AN INTERNATIONAL ATOM                                        33
  SUGGESTED REFERENCES                                                35


                 United States Atomic Energy Commission
                   Division of Technical Information
           Library of Congress Catalog Card Number: 63-64918
                           1963; 1964 (Rev.)

    [Illustration: The cover is a time-exposed photograph of an animated
    model of a uranium-235 atom. The center represents the nucleus,
    greatly exaggerated in size. The fine lines represent the electrons
    whirling about the nucleus.
    Courtesy Union Carbide Corporation]

C. JACKSON CRAVEN is a teacher’s teacher as well as a student’s teacher,
and has had an active career aiding understanding of atomic energy as a
member of the University of Tennessee faculty and on the staff of the
Oak Ridge Institute of Nuclear Studies. He has conducted short courses
to instruct groups of high school science teachers in nuclear energy,
and has served in a key capacity in training Institute
demonstration-lecturers who visit high schools throughout the nation.

Dr. Craven worked during World War II for the Manhattan Project, which
built the first atomic bomb. He earned bachelor’s and graduate degrees
at the University of North Carolina, and later taught physics and
mathematics at Delta State Teachers College and at Furman and Emory
Universities.

His research interests include infrared spectroscopy, gaseous diffusion
through porous media, and the physical properties of fibers.



                            OUR ATOMIC WORLD


                          By C. Jackson Craven

  _The story of atomic energy evolves from the curiosity of people
  concerning the nature and structure of matter, the stuff of which all
  material things are made._



                  The Greeks Were Curious About Matter


Certain philosophers of ancient Greece—Democritus for one—were
fascinated by the question: _what is matter?_ You can imagine one of the
philosophers saying to his pupils:

“Gentlemen, let us consider a piece of cheese. With a knife we can cut
it in two, thus obtaining smaller pieces. We can then cut one of these
smaller pieces in two, obtaining still smaller pieces. We can _think_
about repeating this process over and over to get smaller and smaller
pieces of cheese. Now can this process be continued without limit, or
will a time come when we arrive at the smallest possible piece of
cheese? In other words, is there a piece so small that we must have at
least that much or none, with no choice in between?”

It is probable that most people who thought about this question at all
during the next two thousand years answered the last question in the
negative. The prevailing notion was that matter was continuous, with no
theoretical limit as to how small a piece of cheese, or anything else,
might be.

This concept was humorously expressed by the British mathematician
Augustus De Morgan (1806-1871) in these lines:

  _Great fleas have little fleas upon their backs to bite ’em,
  And little fleas have lesser fleas, and so, ad infinitum._



                     The Atomic Theory Is Confirmed


De Morgan evidently did not keep up with the latest developments in
science, however, because two years before his birth, John Dalton, an
English schoolteacher, had changed the atomic theory of matter from a
philosophical speculation into a firmly established principle. The
evidence that convinced Dalton and many other contemporary scientists of
the reality of atoms came from quantitative chemical analysis.

Dalton knew that many chemical substances could be separated into two or
more simpler substances. Chemicals that could be separated further were
called compounds; those that could not were called elements. Careful
experiments by Dalton and others showed that whenever two or more
elements combined chemically to make a compound the relative amounts of
the elements had to be carefully adjusted to fit a definite proportion
in order to have no elements left over after the reaction was finished.
For example, if hydrogen and oxygen were combined to form water, the
weight of oxygen had to be eight times the weight of hydrogen;
otherwise, either some hydrogen or some oxygen would be left over.

This fundamental truth is now called the Law of Definite Proportions.
Another important principle, called the Law of Multiple Proportions, is
illustrated by hydrogen peroxide, which is made up of the same two
elements that are found in water. The weight of oxygen in hydrogen
peroxide, however, is 16 times the weight of hydrogen or exactly twice
the relative weight found in water.

These principles of chemical combination convinced Dalton that each
chemical element consists of small, indivisible units, all just alike,
called atoms, and that each chemical compound also has basic units,
called molecules, which cannot be divided without reducing the compound
into its elements—that is, destroying it as a compound. He visualized a
molecule of a compound as formed by the uniting of individual atoms of
two or more elements. It was obvious to him that in any molecule of a
compound, the weight of each atom of a component element bore a
proportionate relationship to the weight of the entire molecule which
was equal to the proportion, by weight, of all that element in the
compound. And although Dalton had no idea how heavy any individual atom
really was, he could tell how many _times_ heavier or lighter it was
than an atom of another element.

Incidentally, Dalton mistakenly thought that one atom of oxygen was
eight times as heavy as one atom of hydrogen instead of 16 times as
heavy. He assumed a water molecule to be HO instead of H₂O.



             Cathode Rays Show Atoms Contain Smaller Parts


Curiosity about the fundamental nature of matter was matched by equally
avid curiosity about the fundamental nature of electricity. Before 1850
much had been learned about the behavior of electric charge and electric
currents flowing through solids and liquids. Real progress in
understanding electric charge, however, had to wait for the development
of highly efficient vacuum pumps.

About 1854 Heinrich Geissler, a German glassblower, developed an
improved suction pump, and also succeeded in sealing into a glass tube
two wires attached to metal electrodes inside the tube. Experimenters
were then able to study the flow of electricity through a near-vacuum. A
Geissler tube is diagramed in Figure 1.

By the 1890s it had become clear that the flow of electricity through a
highly evacuated tube consisted of a negative electric charge moving at
a very high speed along straight lines between sealed-in electrodes.
Since it originated at the negative electrode, or cathode, the invisible
stream of charge was named “cathode rays.”

    [Illustration: Figure 1 _Geissler Tube._]

  CURRENT SOURCE
  CATHODE (-)
    STREAM OF ELECTRONS
    VACUUM PUMP
  ANODE (+)

Although many investigators contributed to knowledge about cathode rays,
the experiments of Joseph J. Thomson, a British physicist, are generally
considered to have been the most enlightening. Thomson arranged a
cathode-ray tube so that the rays could be deflected by magnets and by
electrically charged metal plates. By applying certain well-known
principles of physics, he was able to confirm an impression already held
by physical chemists, namely, that electric charge, like matter, was
“atomized”—the stream of charge consisted of a swarm of very small
particles, all alike. He succeeded also in determining that the speed of
the particles was about one-tenth the speed of light.

Probably Thomson’s most significant result was determining the ratio of
the charge of each little particle to its weight. He was able to do this
by measuring the magnetic force required to divert a stream of charged
particles. (You can do this experiment yourself with relatively simple
equipment.) This charge-to-weight ratio proved to be nearly 2000 times
greater than the already known charge-to-weight ratio for a positively
charged hydrogen atom, or ion, which until then was thought to be the
lightest constituent of matter. It remained to be determined whether
charge or weight caused the difference. Further experimentation showed
that the charges were approximately the same amount in the two cases. It
was therefore proven that the weight of the hydrogen atom, lightest of
all the atoms, was nearly 2000 times as great as the weight of one of
the little negative particles.

The name “electron” was given to the small negative particles identified
by Thomson. Since the electrons had come from the cathode, it was
apparent that the atoms in the cathode must contain electrons. Thomson
reasoned that electric current in a wire is a stream of electrons
passing successively from atom to atom and that the difference between
an electrically charged atom and a neutral atom is that the charged one
has gained or lost one or more electrons.



                      Radioactive Atoms Discovered


    [Illustration: _Henri Becquerel_
    Courtesy Journal of Chemical Education, Discovery of the Elements,
    Mary Elvira Weeks.]

In 1896 the French physicist Henri Becquerel was investigating the
relation between fluorescence and X rays, a puzzling kind of penetrating
radiation discovered a few months earlier by the German, Wilhelm
Roentgen. Various chemical compounds fluoresce, or glow, when exposed to
ultraviolet rays and other types of radiation. While experimenting with
a large number of chemicals, Becquerel discovered, quite by accident,
that a compound containing the element uranium can, without being
exposed to any kind of radiation, darken a photographic plate completely
wrapped in heavy black paper.

Although no one realized it at the time, Becquerel had discovered that
atoms of some elements will at random times transform themselves into
atoms of a different element by emitting certain extremely high-speed
charged particles. Atoms that can do this are said to be radioactive,
and it was the radiation from transforming uranium atoms that darkened
Becquerel’s photographic plate.



                  Rutherford Finds the Atomic Nucleus


    [Illustration: _Ernest Rutherford, 1871-1937_
    Courtesy Nobelstiftelsen]

We are greatly indebted to the imagination and experimental skill of the
British physicist Ernest Rutherford for the interpretation of
radioactivity in terms of the structure of atoms.

Rutherford, born and educated in New Zealand, moved to England to work
under Thomson at Cambridge University in 1895. Shortly afterward,
Wilhelm Roentgen in Germany discovered X rays, Becquerel in France
discovered radioactivity, and Thomson proved the existence of the
electron.

During the next few years, curiosity about the fundamental nature of
radioactivity led a number of people to do a great deal of work. The
element thorium was found to be radioactive, and Marie and Pierre Curie
discovered two new elements, polonium and radium, that were also
radioactive. The radiation from radioactive materials was found to be of
three kinds called alpha rays, beta rays, and gamma rays. Alpha rays
were first detected by Rutherford, who later identified them as
positively charged helium atoms. Becquerel demonstrated that beta rays,
like cathode rays, consist of negatively charged electrons. The highly
penetrating gamma rays were proved by Rutherford and E. N. da C. Andrade
to be electromagnetic radiation similar to X rays.

Rutherford, in collaboration with the English chemist Frederick Soddy,
brought order out of a chaos of puzzling discoveries by establishing the
general behavior of radioactive atoms. He determined that certain
naturally occurring atoms of high atomic weight can spontaneously emit
an alpha or a beta particle and thereby convert themselves into new
atoms. These new atoms, being also radioactive, sooner or later convert
themselves into still different atoms, and so on. Each time an alpha
particle is emitted in this sequence, the new atom is lighter by the
weight of the alpha particle, or helium atom. The disintegration process
proceeds from stage to stage until at last a _stable_ atom is produced.
The end product in this “decay” process in naturally occurring
radioactive elements is lead.

One experiment by Rutherford and his co-workers had a most profound
effect on the understanding of atomic structure. What they did was to
direct a stream of alpha particles at a thin piece of gold foil. The
results were astonishing. Almost all the particles passed straight
through the foil without changing direction. Of the few particles that
did ricochet in new directions, however, some were deflected at very
sharp angles. (See Figure 2.)

    [Illustration: Figure 2 _Rutherford’s most famous experiment, which
    led him to the concept of the nucleus._]

As a result of this experiment, Rutherford proposed a concept of the
atom entirely different from the one which prevailed at this time. The
prevailing notion was one advanced by Thomson which conceived of an atom
as a blob of positive electric charge in which were imbedded, in much
the same way as plums are in a pudding, enough electrons to neutralize
the positive charge. Rutherford’s concept, which quickly set aside
Thomson’s “plum pudding” model, was that an atom has all of its positive
charge and virtually all of its mass concentrated in a tiny space at its
center. (Collisions with this center, which came to be known thereafter
as the nucleus, had been responsible for the sharp changes in direction
of some of the alpha particles.) The space surrounding this nucleus is
entirely empty except for the presence of a number of electrons (79 in
the case of the gold atom), each about the same size as the nucleus.

To illustrate Rutherford’s concept, let us imagine a gold atom magnified
so that it is as large as a bale of cotton. The nucleus at the center of
this large atom would be the size of a speck of black pepper. If this
imaginary bale weighed 500 pounds, the little speck at its center would
weigh 499¾ pounds; the surrounding cotton (corresponding to empty space
in Rutherford’s concept) containing the 79 electrons would weigh but ¼
pound. To express this idea another way, any object such as a gold ring,
as dense and solid as it may seem to us, consists almost entirely of
nothing!



                        The Proton Is Recognized


Rutherford’s discovery aroused intense curiosity about the nature and
possible structure of this extremely small, but all-important, part of
an atom. It was assumed that the positive charge carried by the nucleus
must be a whole-number multiple of a small unit equal in size but
opposite in sign to the charge of an electron. This conclusion was based
on the information that all atoms contain electrons and that an
undisturbed atom is electrically neutral. Since it was known that a
neutral atom of hydrogen contains just one electron, it appeared that
the charge on a hydrogen nucleus must represent the fundamental unit of
positive charge, some multiple of which would represent the charge on
any other nucleus. Several lines of investigation combined to establish
quite firmly that nuclei of atoms occupying adjacent positions on the
periodic chart of the elements differed in charge by this fundamental
unit. Since the hydrogen nucleus seemed to play such an important role
in making up the charges of all other nuclei, it was given the name
proton from the Greek “protos,” which means “first.”



                        Isotopes Are Discovered


At a historic meeting of the British Association for the Advancement of
Science held in Birmingham, England, in 1913, two apparently unrelated
lines of investigation were reported, each of which showed that some
atomic nuclei have identical electric charges but different weights.

One report was presented by Frederick Soddy, who had collaborated with
Rutherford in explaining the pattern of natural radioactivity. Soddy
knew that the nucleus of a radioactive atom loses both weight and
positive charge when it throws out an alpha particle (helium nucleus).
On the other hand, when a nucleus emits a beta particle (negative
electron), its positive charge increases, but its weight is practically
unchanged. Thus Soddy could deduce the weights and nuclear charges of
many radioactive products. In several cases the products of two
different kinds of radioactivity had the same nuclear charge but
different weights. Since it is the positive charge carried by the
nucleus of an atom which fixes the number of negative electrons needed
to complete the atom, the nuclear charge is really responsible for the
exterior appearance, or chemical properties, of the atom.

This conclusion was confirmed by unsuccessful efforts to separate by
chemical means different radioactive products having the same nuclear
charge but different weights. The products might have had quite
different rates of radioactive disintegration, but they appeared to
consist of chemically identical atoms of the same chemical element and
hence to belong at the _same place_ on the periodic chart of the
elements. Soddy suggested that such atoms be called _isotopes_, from a
Greek word meaning “same place.”

At the same meeting, Francis W. Aston, an assistant of Thomson,
described what happened when charged atoms, or ions, of neon gas were
accelerated in a discharge tube similar to the cathode-ray tube in which
Thomson had discovered the electron. The rapidly moving neon ions were
deflected by a magnet. Since light objects are more easily deflected
than heavy objects, the amount of deflection indicated the weight. By
making a comparison with a familiar gas like oxygen, Thomson and Aston
were actually able to measure the atomic weight of neon. To their
surprise they found two kinds of neon. About nine-tenths of the neon
atoms had an atomic weight of 20, and the remainder an atomic weight of
22.

What Thomson and Aston had done was to show that the stable element neon
is a mixture of two isotopes. A device that can do what their apparatus
did is called a mass spectrograph. (See Figure 3.) Since their time,
instruments of this type have shown that more than three-fourths of the
stable chemical elements are mixtures of two or more stable isotopes; in
fact, there are about 300 such isotopes in all. The number of known
unstable radioactive isotopes (radioisotopes), natural or man-made, is
greater than 1000 and is still growing!

    [Illustration: Figure 3 _Mass spectrograph as used by Thomson and
    Aston to measure the atomic weight of neon._]

  NEON 20
  NEON 22



                    The Alchemists’ Dream Comes True


During the Middle Ages the desire to find a way to convert a base metal
like lead into gold was the outstanding incentive for research in
chemistry. When the important role of the nucleus in determining the
chemical properties of an atom became clear and the natural
transmutation accompanying radioactivity was understood, the fascinating
idea occurred to many people that perhaps man would soon be able to
alter the nucleus of a stable atom and thus deliberately convert one
element into another. In a historic lecture delivered in Washington, D.
C., in April 1914, Rutherford said, “It is possible that the nucleus of
an atom may be altered by direct collision of the nucleus with very
swift electrons or atoms of helium (i.e., beta or alpha particles) such
as are ejected from radioactive matter.... Under favorable conditions,
these particles must pass very close to the nucleus and may either lead
to a disruption of the nucleus or to a combination with it.”

    [Illustration: _Medieval Alchemist_
    Courtesy Fisher Scientific Company]

World War I began shortly after Rutherford made this statement, and
preoccupation with war work stopped his experiments with nuclei. In
1919, however, he published a paper describing what happens when alpha
particles pass through nitrogen gas. Very fast protons, or hydrogen
nuclei, appear to originate along the paths of the alpha particles. The
following is from Rutherford’s paper:

“If this be the case, we must conclude that the nitrogen atom is
disintegrated under the intense forces developed in a close collision
with a swift alpha particle, and that the hydrogen atom which is
liberated formed a constituent part of the nitrogen nucleus.... The
results as a whole suggest that, if alpha particles or similar
projectiles of still greater energy were available for experiment, we
might expect to break down the nuclear structure of many of the lighter
atoms.”

This prediction has certainly been verified through the use of the
atomic artillery provided by extremely powerful particle accelerators,
or “atom smashers.”[1]

    [Illustration: _The Bevatron accelerator at the University of
    California’s Lawrence Radiation Laboratory, Berkeley, California,
    shown after recent remodeling in which it was enclosed in concrete
    shielding._
    Courtesy Lawrence Radiation Laboratory]

Patrick Blackett in England and W. D. Harkins in the United States soon
proved independently that, during the nuclear event reported by
Rutherford in his 1919 paper, an alpha particle combines with a nitrogen
nucleus and that the resulting unstable combination immediately emits a
proton and ends up as one of the isotopes of oxygen. This was the first
instance of deliberate transmutation of one stable chemical element into
another. Since that time practically every known element has been
transmuted by bombardment. The dream of the alchemists has been
partially fulfilled in that mercury has been changed into gold. We say
“partially fulfilled” because the process is much too expensive to be
economically profitable.



                 Some Particles Have No Electric Charge


During the early 1920s a number of investigators, including Harkins in
the United States, Orme Masson in Australia, and Rutherford and his
assistant James Chadwick in England, seriously considered the
possibility that a neutral particle might exist in nature, possibly
formed by the very close association of a proton and an electron.
However, strenuous efforts to produce such particles by combining
protons and electrons were unsuccessful.

During these years the new technique of bombarding all kinds of matter
with alpha particles to see what would happen was widely exploited, and
it gradually became clear that in a few instances a peculiar and highly
penetrating kind of radiation was produced. In 1932, Chadwick succeeded
in showing that the peculiar radiation must consist of a stream of
particles, each weighing about the same as a proton but having no
electrical charge.

The name “neutron” for a possible neutral particle of this type was
suggested by Harkins in the United States in 1921. Much evidence now
exists that the neutron is a fundamental particle in its own right and
that it should not be thought of merely as a particle formed by a very
close association between a proton and an electron.

The new particle discovered by Chadwick was destined to play a totally
unexpected role, not only in the history of atomic science but also in
the fate of nations. It immediately outmoded a previous concept of the
nucleus that pictured it as a cluster of protons approximately half of
which were neutralized by electrons crowded into the nucleus. A nucleus
is now thought of as containing just protons and neutrons.

The neutron was also greeted by nuclear workers as a practically perfect
kind of bullet. Unlike charged alpha particles, uncharged neutrons can
approach a charged nucleus completely unopposed. It is physically
impossible for any kind of container to hold a swarm of free neutrons;
they seep right through its walls.



                   Matter Is Energy; Energy Is Matter


So far, in the story about man’s curiosity concerning the fundamental
nature and structure of matter, the development of ideas about
_structure_ has been emphasized. We will now take a brief look at a
development which strongly influenced our ideas about the fundamental
_nature_ of matter.

In 1887 reports appeared on a famous study, often referred to as the
Michelson-Morley experiment, which was aimed at determining the earth’s
speed through absolute space. The entirely unexpected results of the
experiment had a great impact on the concepts of space and time. We will
here concern ourselves with just one outcome of the experiment.

In 1905, a young German-born physics student named Albert Einstein, who
was working as a patent examiner in Switzerland, published three papers,
each of which had a profound effect on a different field of physics.

One of the papers dealt with some peculiar speculations about space and
time which began to interest him when he was studying the
Michelson-Morley experiment. The contents of the paper are now referred
to as the Special Theory of Relativity. This paper contains several
predictions that seemed incredible to the average physicist of that day.
These predictions have, however, long since been proved valid.

    [Illustration: _Albert Einstein in 1905._
    Courtesy Lotte Jacobi, Hillsboro, New Hampshire]

One of Einstein’s predictions had to do with the equivalence of matter
and energy. Until 1905 _matter_ had been considered as something that
has mass or inertia; _energy_, on the other hand, had been regarded as
the ability to do work. It was believed that the two were as different
from each other as, say, a square yard is different from an hour.
Einstein’s theory, however, implies that matter and energy are merely
two different manifestations of the same fundamental physical reality,
and that each may be converted into the other according to the famous
equation:

                                  E = MC²

  where
      E = quantity of energy,
      M = quantity of matter, and
      C = speed of light in a vacuum.



                         Nuclei Contain Energy


One more piece of information must be fitted into the story of the atom
before it becomes clear why some people began to realize during the
1920s that atomic nuclei contain vast stores of energy that might some
day revolutionize civilization. This last item has to do with a nuclear
phenomenon known as the packing fraction.

Since any nucleus consists of a certain number of protons and neutrons,
it seems logical that the total weight of the nucleus could be
determined by adding together the individual weights of the particles in
it. When mass spectrographs of sufficiently high accuracy became
available, however, it was found that in the case of nuclear weights,
the whole was not equal to the sum of its parts! All nuclei (except
hydrogen) weigh less than the sum of the weights of the particles in
them.

For example, the atomic weight of a proton is 1.00812 and that of a
neutron is 1.00893. (These are relative weights based on an
internationally accepted scale.) It would seem then that a nucleus of
helium containing two protons and two neutrons should have an atomic
weight of 2 × 1.00812 plus 2 × 1.00893 or 4.0341. Actually the atomic
weight of helium as measured by the mass spectrograph is only 4.0039.
(See Figure 4.)

    [Illustration: Figure 4 _A case where the whole is not equal to the
    sum of its parts. Two protons and two neutrons are distinctly
    heavier than a helium nucleus, which also consists of two protons
    and two neutrons. Energy makes up the difference._]

  HELIUM NUCLEUS
  TWO PROTONS AND TWO NEUTRONS

What happens to the missing atomic weight of 0.0302? Physicists now
realize that, as postulated in Einstein’s formula, it must be converted
into energy! The conversion occurs when the protons and neutrons are
drawn together into a helium nucleus by the powerful nuclear forces
between them.

When the missing atomic weight 0.0302 is multiplied by the square of the
velocity of light according to Einstein’s theory, it is found to
represent a tremendous amount of energy. Indeed, the energy released in
forming a helium nucleus from two protons and two neutrons turns out to
be seven million times that released when a carbon atom combines with an
oxygen molecule to produce a molecule of carbon dioxide in the familiar
process of combustion.

The general behavior of such losses in atomic weight for atoms
throughout the periodic table had been determined as early as 1927,
largely through the work of Aston, the English scientist who developed
the first mass spectrograph. His results show that, in general, if two
light nuclei combine to form a heavier one, the new nucleus does not
weigh as much as the sum of the original ones. This behavior continues
up to the level of the so-called “transition metals”—iron, nickel, and
cobalt—in the periodic table. But if two nuclei heavier than iron are
coalesced into a single very heavy nucleus found near the end of the
periodic table (such as uranium), the new nucleus weighs more than the
sum of the two nuclei that formed it.

Thus, if a very heavy nucleus could be divided into parts, energy would
be released, and the sum of the weights of the fragments would be less
than that of the original nucleus.

In these two types of nuclear reactions, a small amount of matter would
actually vanish! Einstein’s Special Theory of Relativity states that the
vanished matter would reappear as an enormous quantity of energy.

During the late 1920s scientists began saying that a small amount of
matter could supply enough energy to drive a large ship across the
ocean. As we know, this prediction has since been borne out by the
performance of nuclear submarines and surface vessels.

    [Illustration: _The NS_ Savannah _was the first cargo-passenger ship
    to be driven by nuclear power_.
    Courtesy States Marine Lines]

    [Illustration: _The_ Nautilus _was the Navy’s first atomic-powered
    submarine_.
    Courtesy U. S. Navy]



                               CHRONOLOGY


  1800          Dalton firmly establishes atomic theory of matter.
  1890-1900     Thomson’s experiments with cathode rays prove the
                existence of electrons. Atoms are found to contain
                negative electrons and positive electric charge.
                Becquerel discovers unstable (radioactive) atoms.
  1905          Einstein postulates the equivalence of mass and energy.
  1911          Rutherford recognizes nucleus.
  1919          Rutherford achieves transmutation of one stable chemical
                element (nitrogen) into another (oxygen).
  1920-1925     Improved mass spectrographs show that changes in mass per
                nuclear particle accompanying transmutation account for
                energy released by nucleus.
  1932          Chadwick identifies neutrons.
  1939          Discovery of uranium fission by German scientists.
  1940          Discovery of neptunium by Edwin M. McMillan and Philip H.
                Abelson and of plutonium by Glenn T. Seaborg and
                associates at the University of California.
  1942          Achievement of first self-sustaining nuclear reaction,
                University of Chicago.
  1945          First successful test of an atomic device, near
                Alamagordo, New Mexico, followed by the dropping of
                atomic bombs on Hiroshima and Nagasaki, Japan.
  1946          U. S. Atomic Energy Commission established by Act of
                Congress.
                First shipment of radioisotopes from Oak Ridge goes to
                hospital in St. Louis, Missouri.
  1951          First significant amount of electricity (100 kilowatts)
                produced from atomic energy at testing station in Idaho.
  1952          First detonation of a thermonuclear bomb, Eniwetok Atoll,
                Pacific Ocean.
  1953          President Eisenhower announces U. S. Atoms-for-Peace
                program and proposes establishment of an international
                atomic energy agency.
  1954          First nuclear-powered submarine, _Nautilus_, commissioned.
  1955          First United Nations International Conference on Peaceful
                Uses of Atomic Energy held in Geneva, Switzerland.
  1957          First commercial use of power from a civilian reactor
                takes place in California.
                Shippingport Atomic Power Plant in Pennsylvania reaches
                full power of 60,000 kilowatts.
                International Atomic Energy Agency formally established.
  1959          First nuclear-powered merchant ship, the _Savannah_,
                launched at Camden, New Jersey.
                Commissioning of first nuclear-powered Polaris
                missile-launching submarine _George Washington_.
  1961          A radioisotope-powered electric power generator placed in
                orbit, the first use of nuclear power in space.
  1962          Nuclear power plant in the Antarctic becomes operational.
  1963          President Kennedy ratified the Limited Test Ban Treaty
                for the United States on October 7.
  1964          President Johnson signed law permitting private ownership
                of certain nuclear materials.



                          Fission is Explained


    [Illustration: _Enrico Fermi 1901-1954_
    Courtesy Chemical and Engineering News]

Physicists welcomed the neutron as a bullet that could strike any
nucleus, unopposed by electric repulsion. During the middle 1930s, a
number of investigators, chief among them the Italian physicist Enrico
Fermi, exposed many different isotopes of the chemical elements to beams
of neutrons to see what would happen.

What usually happened was that the bombarded nuclei would absorb
neutrons, emit alpha, beta, or gamma rays, and change into different
isotopes. The identification of the extremely small quantities of
isotopes produced required the development of a fantastic new branch of
chemistry known as radiochemistry, or, as one chemist put it, “phantom
chemistry.”

In some cases the absorption of a neutron by a nucleus was followed by
the emission of a negative electron (beta particle). This produced an
atom whose nuclear positive charge had been increased by one unit and
which therefore belonged at the next higher place on the periodic table.
Fermi and others then considered the fascinating possibility of doing
the same thing to uranium, the last-known element on the periodic table,
to create previously unknown chemical elements. The results of
bombarding uranium with neutrons turned out to be extremely complex, but
it eventually became clear that “transuranic” elements (those heavier
than uranium) could actually be made in this way.[2]

Some of the complex results of bombarding uranium with neutrons formed
an intriguing puzzle that kept various investigators busy for several
years. In 1939 the German chemists Otto Hahn and Fritz Strassmann and
the physicists Lise Meitner and Otto Frisch were able to announce a
solution. The absorption of a neutron by a certain uranium nucleus
(later shown to be that of the relatively rare isotope uranium-235) can
result in a splitting, or _fission_, of the nucleus into two parts with
separate weights that place them somewhere near the middle of the
periodic table.

    [Illustration: _Lise Meitner and Otto Hahn in their laboratory in
    the 1930s._
    Courtesy Addison-Wesley Publishing Co.]

The announcement of this discovery created quite a stir among physicists
because a nuclear process of this nature must release a very large
amount of energy.

    [Illustration: _Scale model of the CP-1 (Chicago Pile No. 1) used by
    Enrico Fermi and his associates on December 2, 1942, to achieve the
    first self-sustaining nuclear reaction. Alternate layers of
    graphite, containing uranium metal and/or uranium oxide, were
    separated by layers of solid graphite blocks. Graphite was used to
    slow down neutrons to increase the likelihood of fissions._]

The excitement among physicists became even greater when it was realized
that this newly discovered process of fission was accompanied by the
release of several free neutrons from the splitting nucleus. Each new
neutron could, if properly slowed down by a moderating material, cause
another nucleus to split and release more energy and still more
neutrons, and so on, as illustrated in Figure 5. (A moderator is
necessary because fast, newly released neutrons are too readily absorbed
by uranium-238 nuclei, which rarely split.) Apparently all that was
needed to achieve this spectacular kind of a chain reaction was to
assemble enough uranium in one place so that the released neutrons would
have a good chance of finding another ²³⁵U nucleus before escaping from
the pile. The amount of fissionable material required to sustain a chain
reaction is termed the “critical mass.” A team of scientists led by
Fermi achieved the first self-sustaining nuclear reaction on December 2,
1942, under the grandstand at the University of Chicago’s athletic
field. This date is often referred to as the beginning of the Nuclear
Age.

    [Illustration: Figure 5 _This diagram shows what happens in a chain
    reaction resulting from fission of uranium-235 atoms._]

  STRAY NEUTRON
  ²³⁵U
  ORIGINAL FISSION
    FISSION FRAGMENTS
    One to three neutrons from fission process
    A NEUTRON SOMETIMES LOST
  ²³⁸U
    CHANGES TO PLUTONIUM
  ²³⁵U
    ONE NEW FISSION
    FISSION FRAGMENT
    One to three neutrons again
  ²³⁵U
  ²³⁵U
    TWO NEW FISSIONS
    FISSION FRAGMENTS



                      The Fission Bomb Is Exploded


The American scientists present on that historic December day were part
of the tremendous super-secret scientific and industrial complex that
bore the unrevealing title Manhattan District. The United States had
been at war almost a year. An uncontrolled fission reaction gave promise
of producing an explosion of untold proportions. This promise, coupled
with the possibility that enemy scientists might be nearing such a goal,
had launched a vast Allied effort.

The Manhattan Project, as it was commonly known, included a variety of
“hush-hush” facilities. Each of these installations, in New York,
Illinois, Tennessee, New Mexico, California, and Washington, had its own
experts working night and day to solve the baffling problems surrounding
development of a fission weapon.

Ordinary uranium as found in nature was not suitable for an atomic bomb
because less than one percent of the atoms in it are fissionable isotope
²³⁵U.[3] It therefore became necessary to find some means for separating
the rare ²³⁵U from the large quantity of ²³⁸U. Chemistry could not do it
since the two isotopes are identical chemically.

Several methods of achieving large-scale separation were tried. The most
successful and economical, known as “gaseous diffusion,” involves
compressing normal uranium, in the form of uranium hexafluoride gas,
against a porous barrier containing millions of holes, each smaller than
two-millionths of an inch. Since the ²³⁵U molecules are slightly lighter
than the ²³⁸U, they bounce against the barrier more frequently and have
a greater chance of penetrating. Thus, although the gas at first
contains only 0.7% ²³⁵U, the process of compression is repeated several
thousand times, and the proportion gradually increases until the
necessary concentration is reached.

For this operation an enormous plant containing a very large barrier
area, miles of piping, and countless pumps was built at Oak Ridge,
Tennessee.

At the same time that vast efforts were being made to produce a ²³⁵U
bomb, another project of equal importance was being pursued to develop a
different kind of fission bomb. Uncertainty as to whether it would be
possible to separate usable amounts of ²³⁵U led to a decision to exploit
a highly significant discovery about one of the transuranic elements.

By 1941 Glenn T. Seaborg, Edwin M. McMillan, Philip H. Abelson, and
others at the Radiation Laboratory, Berkeley, California, had identified
isotopes of two new transuranic elements developed when they bombarded
²³⁸U nuclei with neutrons. The new elements were named neptunium and
plutonium after the planets Neptune and Pluto, which lie beyond Uranus
in the solar system.[4] One isotope of plutonium, plutonium-239, which
resulted from the absorption of a neutron by a ²³⁸U nucleus and the
emission of two beta particles, was discovered to be as fissionable as
²³⁵U and hence theoretically just as feasible for a bomb. Since
plutonium is chemically different from uranium, it offered the
tremendous advantage that it could readily be concentrated by
conventional chemical techniques.

The way to manufacture usable amounts of plutonium, an element that had
never before been detected on earth, is to expose uranium to a very
intense neutron bombardment. The best-known place to find a rich supply
of neutrons was the heart of a self-sustaining chain-reacting pile of
uranium. Accordingly, very large piles, or _reactors_, were rushed to
completion near the Columbia River at Hanford, Washington, to make
plutonium.

    [Illustration: _First atomic bomb explosion at Alamagordo, New
    Mexico, at 5:30 a.m. on July 16, 1945._
    Courtesy U. S. Army]

On July 16, 1945, a plutonium bomb, carefully assembled by another group
of scientists at “Project Y,” Los Alamos, New Mexico, was successfully
tested in the New Mexico desert. The heat from that first man-made
nuclear explosion completely vaporized a tall steel tower and melted
several acres of surrounding surface sand. The flash of light was the
brightest the earth had ever witnessed.

A ²³⁵U bomb was dropped on Hiroshima, Japan, on August 6, 1945. Three
days later a plutonium bomb was dropped on Nagasaki, Japan. Hostilities
ended on August 14, 1945.



                Nuclear Energy Is Needed for the Future


The chief source of the enormous quantities of energy used daily by
modern civilization is fossil fuels in the form of coal, petroleum, and
natural gas. Concentrated sources of these fuels, though large, are far
from inexhaustible, and it has been said that future historians may
refer to the brief time when they were used as “the fossil-fuel
incident.”

    [Illustration: _These lights of downtown Pittsburgh are symbolic of
    the generation of electricity by atomic power from Shippingport,
    Pennsylvania, the site of the world’s first full-scale
    atomic-electric generation station exclusively for civilian needs.
    Homes and factories of the greater Pittsburgh area are receiving the
    electricity produced at the plant and transmitted through the
    Duquesne Light Company system. The Shippingport plant is a joint
    project of Westinghouse Electric Corporation, U. S. Atomic Energy
    Commission, and the Duquesne Light Company._
    Courtesy Westinghouse Electric Corporation]

The next great source of energy will probably be nuclear reactors, in
which controlled chain reactions release energy from the large store of
fissionable materials in the world.[5]

The accomplishments of nuclear power in the propulsion of ships have
already been noted. In addition, there is now going on in industrialized
countries in different parts of the world a large-scale development of
nuclear power plants for production of electricity. Nuclear electric
power is approaching the point where it will be economically competitive
with power from hydroelectric plants or those burning coal, oil, or gas
as fuels. Improvements in nuclear power technology are rapidly being
made, and it is now widely predicted that before the end of this century
most new electric power plants will be nuclear.



                          Fusion Has Potential


One of the greatest puzzles to be solved by physicists arose from the
work of geologists. When it became clear that coal and other fossil
remains of living things date from many hundreds of millions of years
ago, it was obvious that the earth’s sun had been shining at a quite
steady rate for an extremely long time.

How does it manage to do it? What is its source of energy? Chemical
energy supplied by combustion and gravitational potential energy
supplied by contraction are thousands of times too small to have kept
the sun going for such a long time.

The principle illustrated by Figure 4 suggests the most probable source
of energy for the sun and all the other stars as well. It is known that
the sun consists chiefly of hydrogen and that it has a temperature of
about 40,000,000 degrees Fahrenheit near its center. Several kinds of
nuclear reactions produced in atom smashers have demonstrated that
hydrogen nuclei, if energized by being heated to a very high
temperature, can actually combine, or fuse, to form helium nuclei.

The accompanying loss of weight per particle indicated by Figure 4 must
result in the appearance of sufficient energy to balance Einstein’s
famous equation. In fact, calculations by the German-born American
physicist Hans A. Bethe and others show that, based on reasonable
estimates of the conditions within the sun, familiar nuclear reactions
account for its energy. The calculations predict, furthermore, that the
sun can continue to operate at its present level for many billions of
years.

    [Illustration: _Large loop prominences on the sun, caused by a
    locally intense magnetic field. Project Sherwood, the U. S. program
    in controlled fusion, is devoted to research on fusion reactions
    similar to those from which the sun derives its energy._
    Courtesy Sacramento Peak Observatory, AFCRL]

Since fusion of light nuclei is produced by extremely high temperatures,
fusion events are called _thermonuclear reactions_. The possibility of
bringing about thermonuclear reactions on earth to serve as a source of
energy has naturally attracted much attention.

In spite of the fact that fusion of ordinary hydrogen atoms (each of
which has one proton as its nucleus) supports the activity of the sun,
this particular reaction seems to occur much too slowly to be usable on
earth. Other isotopes of hydrogen, called deuterium and tritium,
however, which contain one and two neutrons in their nuclei,
respectively, fuse much more rapidly and seem to be potential earthly
sources of controlled thermonuclear energy.

    [Illustration: _An early phase of a nuclear detonation at Eniwetok
    Atoll during the 1951 tests._
    Courtesy Joint Task Force Three]

The first large-scale application of thermonuclear energy was the
so-called hydrogen bomb, or “H-bomb.” For a brief time an exploding
fission bomb develops a temperature of hundreds of millions of degrees
Fahrenheit, hot enough to cause some light nuclei to fuse. In the
hydrogen bomb, light nuclei of deuterium and/or tritium are exposed to
this temperature during such a fission explosion. The resulting fusion
of these nuclei causes the explosion to be hundreds of times more
powerful than that of the fission device alone. In 1952 the Atomic
Energy Commission test-fired such a thermonuclear device at Eniwetok
Atoll in the Pacific Ocean. The energy released by the highly efficient
device produced an explosion that completely destroyed the coral islet
where it was detonated.

At such extreme temperatures all atoms are stripped of electrons; the
resulting mixture of nuclei and free electrons is called a _plasma_.
Several laboratories are now working on the problems connected with
creating and containing plasma. Ordinary solid containers cannot be
used. On contact with plasma they would instantly vaporize and would
cool the plasma below the temperature necessary for fusion to occur.
Fortunately, however, the particles that make up a plasma, being charged
electrically, respond to forces in a magnetic field. A strong magnetic
field of proper shape exerts a large confining pressure on a body of
plasma in a high-vacuum chamber. Thus plasma can be contained in a small
volume well removed from the walls of the chamber by surrounding the
chamber with suitably designed large magnets or solenoids to create a
“magnetic bottle.” In addition, a sudden increase in the intensity of
the field can compress the plasma; this compression raises the
temperature of the plasma to near that required for fusion.

    [Illustration: _This plasma is being pushed outward by an internal
    magnetic field as instabilities grow on its internal surface. The
    photo was taken by means of fast-shutter photography permitting
    photo sequences at intervals of 3 to 5 millionths of a second._
    Courtesy General Atomic Division, General Dynamics Corporation]

Fusion of light nuclei would be a much “cleaner” source of energy for
peaceful purposes than fission of heavy ones, because the “ashes” of
fission reactions are radioactive while those of fusion (helium atoms)
are not. Great technical difficulties must be overcome, however, before
a controlled thermonuclear reaction is possible. Fusionable material
must be heated to a temperature of over 100 million degrees Fahrenheit
and must be contained long enough for an appreciable amount of fusion to
occur.

The greatest problem encountered to date is the extreme instability of
the plasma and the corresponding difficulty of maintaining it at the
proper temperature longer than a few millionths of a second. Many
physicists now think that the successful exploitation of thermonuclear
energy will not occur for many years. When and if it is achieved,
however, the deuterium present in the oceans of the earth will represent
an almost inexhaustible source of energy.



                        Isotopes Have Many Uses


The ability to produce and control nuclear reactions is affecting, and
will doubtless continue to affect, human life in two outstanding ways.
One way is by making tremendous amounts of energy available, either as
explosions or as energy released from controlled reactions for peacetime
use. The other way is by producing a vast variety of radioactive
isotopes, first in the particle accelerators (“atom smashers”) mentioned
earlier, and now in large quantities in nuclear reactors.

The presence of a radioactive isotope can be detected by instruments
like the familiar Geiger counter; for this reason isotopes make
wonderful tracers. These telltale atoms, which, in effect, continually
cry “Here I am,” can trace the course of a chemical element through any
kind of chemical reaction. Chemists are taking advantage of this new way
of tagging atoms to study reaction patterns that, heretofore, have been
obscure.

As a consequence, a scientist’s ability to synthesize scarce chemicals
is being increased. The exact role of numerous essential trace elements
in the growth and metabolism of living things, including people, is
being studied by the use of tagged atoms.



                         Radioisotopes at Work


    [Illustration: IN MEDICINE: _Iodine-131 reveals spread of thyroid
    cancer in patient’s body._]

    [Illustration: IN SPACE: _Plutonium-238 is the fuel for the atomic
    generator powering this TRANSIT satellite._
    Courtesy The Martin Company]

    [Illustration: IN FOOD PRESERVATION: _Potatoes stored for 18 months
    at 47°F. Potato at right had been irradiated, that on left had
    not._]

    [Illustration: IN INDUSTRY: _Radioactive iridium was used to inspect
    the hull of the carrier_ Independence.
    Courtesy Technical Operations, Inc.]

As sources of radiation, radioactive isotopes are frequently replacing
more expensive and less convenient sources such as radium and X-ray
machines. The medical treatment of diseased tissue has been greatly
expedited by the new sources. In industry many applications of radiation
sources have been made. They are used, for example, in thickness gauging
and in making radiographs to check the quality of large castings. The
sterilization and preservation of food is another promising use for
inexpensive radioactive sources.

As a controllable means for inducing genetic mutations, radioactive
isotopes are speeding up the process of selecting and developing
superior agricultural products. Practically every agricultural research
center in the world has one or more projects under way which involve the
use of isotopes.

Small devices have also been constructed which produce electricity from
heat generated by decay of radioisotopes. Such devices have been used to
power instruments in a remotely located unmanned weather station, a
navigational buoy, a lighthouse, an underwater navigational beacon, and
space satellites. Many additional uses are foreseen for these isotopic
power generators.



                      The Atomic Energy Commission


Following the end of World War II a vigorous controversy developed as to
whether atomic energy development in the United States should continue
under military control or be transferred to civilian control. The
proponents of civilian control won out, and a civilian Atomic Energy
Commission was established by the Atomic Energy Act of 1946. Under this
Act, which was amended in 1954, the AEC manufactures nuclear weapons for
the armed services; produces fissionable materials for both military and
civilian purposes; fosters research and development in the basic
sciences underlying atomic energy and in applications such as power
production and uses of radioisotopes; regulates the activities of
private organizations using atomic energy; and distributes information
about atomic energy. (This booklet is a small example; most of the
information distributed is much more detailed and technical.)

    [Illustration: _President Truman signs the bill creating the U. S.
    Atomic Energy Commission on August 1, 1946. Behind the President,
    left to right: Senators Tom Connally, Eugene D. Millikin, Edwin C.
    Johnson, Thomas C. Hart, Brien McMahon, Warren R. Austin, and
    Richard B. Russell._
    Courtesy United Press International]

Almost all of the AEC’s materials production and research and
development activities are carried out under contract by other
organizations. American industry, universities, and research
organizations also are engaged in widespread atomic energy activities of
their own, subject only to such government regulations as are needed to
protect national security and public health and safety. For example, the
largest atomic electric power plants now in operation in this country
are privately owned, as are numerous small atomic reactors used for
research. At the end of 1962 some 7000 firms, institutions or
individuals in the United States held federal or state licenses giving
them permission to use radioisotopes. The number of persons employed in
atomic energy work in the United States is estimated to be about
140,000, of which only 8000 work for the Federal Government.



                      Toward an International Atom


In December 1953, President Eisenhower, in a memorable address to the
General Assembly of the United Nations, proposed the establishment under
the aegis of the United Nations of an International Atomic Energy Agency
“to serve the peaceful pursuits of mankind.” This proposal captured the
imagination of people everywhere, and negotiations soon began as to the
purpose, structure, scope, and program of such an organization. In
October 1956 an 81-nation United Nations conference unanimously adopted
a statute for the agency, which came into existence a year later with
headquarters in Vienna, Austria. By the end of 1962 the IAEA had 78
member countries. Its most important work has been assisting some of the
less developed nations of the world to begin programs for peaceful use
of atomic energy.

    [Illustration: _On December 8, 1953, President Dwight D. Eisenhower
    proposed before the United Nations General Assembly that an
    International Atomic Energy Agency be established through which all
    nations could share knowledge and materials to develop the peaceful
    uses of atomic energy for the benefit of all mankind. Seated on the
    presidential platform are, left to right, Mr. Dag Hammarskjöld,
    Secretary-General of the U. N., Madame Vijaya Lakshmi Pandit of
    India, President of the General Assembly, and Mr. Andrew Cordier,
    Executive Assistant to the Secretary-General._
    Courtesy United Nations]

    [Illustration: _This 150,000-kilowatt, dual-cycle, boiling-water
    reactor, located 35 miles north of Naples, Italy, on the Garigliano
    River, was built by General Electric under the United States-Euratom
    Joint Program. It achieved criticality on June 5, 1963._]

Even before the international agency became an accomplished fact, the
United States sought on its own to implement the spirit of President
Eisenhower’s proposal. It initiated in 1955 an Atoms-for-Peace Program
under which the United States has made bilateral agreements with some 40
nations for the sharing of information on peaceful uses of atomic energy
and under which the United States has helped other nations to acquire
nuclear reactors and materials for peaceful use.

Mention should also be made of the International Conferences on Peaceful
Uses of Atomic Energy which the United Nations held in Geneva,
Switzerland, in 1955, 1958, and 1964. The 1955 conference was
particularly noteworthy in that it marked the first time that scientists
had met on a worldwide basis to discuss atomic energy. At and following
this meeting much information previously kept secret was made public.



                          Suggested References


Books

_Atomic Energy_, Irene D. Jaworski and Alexander Joseph, Harcourt, Brace
      and World, Inc., New York 10017, 1961, 218 pp., $4.95.

_Atompower_, Joseph M. Dukert, Coward-McCann, Inc., New York 10016,
      1962, 127 pp., $3.50.

_Atoms Today and Tomorrow_ (revised edition), Margaret O. Hyde,
      McGraw-Hill Book Company, New York 10036, 1966, 160 pp., $3.25.

_Basic Laws of Matter_ (revised edition), Harrie S. W. Massey and Arthur
      R. Quinton, Herald Books, Bronxville, New York 10710, 1965, 178
      pp., $3.75.

_Building Blocks of the Universe_ (revised edition), Isaac Asimov,
      Abelard-Schuman, Ltd., New York 10019, 1961, 380 pp., $3.50
      (hardback); $2.70 (paperback) from E. M. Hale and Company, Eau
      Claire, Wisconsin 54701.

_Elements of the Universe_, Glenn T. Seaborg and Evans G. Valens, E. P.
      Dutton and Company, Inc., New York 10003, 1958, 253 pp., $4.95
      (hardback); $2.15 (paperback).

_Inside the Atom_ (revised edition), Isaac Asimov, Abelard-Schuman,
      Ltd., New York 10019, 1966, 197 pp., $4.00.

_Introducing the Atom_, Roslyn Leeds, Harper and Row, Publishers, New
      York 10016, 1967, 224 pp., $3.95.

_Peacetime Uses of Atomic Energy_ (revised edition), Martin Mann, The
      Viking Press, New York 10022, 1961, 191 pp., $5.00 (hardback);
      $1.65 (paperback).

_The Useful Atom_, William R. Anderson and Vernon Pizer, The World
      Publishing Company, Cleveland, Ohio 44102, 1966, 185 pp., $5.75.

_Secret of the Mysterious Rays: The Discovery of Nuclear Energy_, Vivian
      Grey, Basic Books, Inc., Publishers, New York 10016, 1966, 120
      pp., $3.95.

_The Heart of the Atom: The Structure of the Atomic Nucleus_, Bernard L.
      Cohen, Doubleday and Company, Inc., New York 10017, 1967, 120 pp.,
      $3.95 (hardback); $1.25 (paperback).

_The Questioners: Physicists and the Quantum Theory_, Barbara L. Cline,
      Thomas Y. Crowell Company, New York 10003, 1965, 274 pp., $5.00.

_The Atom and Its Nucleus_, George Gamow, Prentice-Hall, Inc., Englewood
      Cliffs, New Jersey 07632, 1961, 153 pp., $1.95.

_The Atomic Energy Deskbook_, John F. Hogerton, Reinhold Publishing
      Corporation, New York 10022, 1963, 673 pp., $11.00.

_Atomic Energy Encyclopedia in the Life Sciences_, Charles W. Shilling
      (Ed.), W. B. Saunders Company, Philadelphia, Pennsylvania 19105,
      1964, 474 pp., $10.50.

_Atoms for Peace_ (revised edition), David O. Woodbury, Dodd, Mead and
      Company, New York 10016, 1965, 275 pp., $4.50.

_Manhattan Project_, Stephane Groueff, Little, Brown and Company,
      Boston, Massachusetts 02106, 1967, 372 pp., $6.95.

_The New World, 1939/1946_, Volume 1—History of the United States Atomic
      Energy Commission, Richard G. Hewlett and Oscar E. Anderson, Jr.,
      The Pennsylvania State University Press, University Park,
      Pennsylvania 16802, 1962, 766 pp., $5.50.

_Sourcebook on Atomic Energy_ (third edition), Samuel Glasstone, D. Van
      Nostrand Company, Inc., Princeton, New Jersey 08540, 1967, 883
      pp., $9.25.

_The World of the Atom_, 2 volumes, Henry A. Boorse and Lloyd Matz
      (Eds.), Basic Books, Inc., Publishers, New York 10016, 1966, 1873
      pp., $35.00.


Motion Pictures

Available for loan without charge from the AEC Headquarters Film
Library, Division of Public Information, U. S. Atomic Energy Commission,
Washington, D. C., and from other AEC film libraries.

Each of the following motion pictures explains atomic structure,
fission, and the chain reaction. Additional contents are listed below
with the film.

_A Is for Atom_, 15 minutes, sound, color, 1964. Produced by the General
      Electric Company. This film discusses natural and artificially
      produced elements, stable and unstable atoms, principles and
      applications of nuclear reactors, and the benefits of atomic
      radiation to biology, medicine, industry, and agriculture. (Level:
      elementary through high school.)

_Atomic Energy_, 10 minutes, sound, black and white, 1950. Produced by
      Encyclopedia Britannica Films, Inc. The film explains nuclear
      synthesis and shows how, through photosynthesis, the sun’s energy
      is stored on earth and released through combustion. (Level:
      intermediate through high school.)

_Controlling Atomic Energy_, 13½ minutes, sound, color, 1961. Produced
      by United World Films, Inc. This film gives a summary explanation
      of the following: radioactive atoms, radioactivity measurement,
      nuclear reactors, and the production and application of
      radioisotopes in biology, medicine, industry, agriculture, and
      research. (Level: 5th through 8th grades.)

_Introducing Atoms and Nuclear Energy_, 11 minutes, sound, color, 1963.
      Produced by Coronet Instructional Films. This film discusses
      nuclear fusion in the sun and, very briefly, the uses of nuclear
      energy. (Level: 4th through 9th grades.)

_Atomic Physics_, 90 minutes, sound, black and white, 1948. Produced by
      the J. Arthur Rank Organisation, Inc. This film discusses in
      detail the history and development of atomic energy with emphasis
      on nuclear physics. Dalton’s basic atomic theory, Faraday’s early
      electrolysis experiments, and Mendeleev’s periodic table, the
      investigation of cathode rays, discovery of the electron, how the
      nature of positive rays was established, and the discovery of X
      rays are among the historical highlights. Explanation is presented
      of the work of the Joliot-Curie’s and Chadwick in the discovery of
      the neutron, and the splitting of the lithium atom by Cockcroft
      and Walton. Einstein tells how their work illustrates his theory
      of equivalence of mass and energy. (Level: high school.)

_Unlocking the Atom_, 20 minutes, sound, black and white, 1950. Produced
      by United World Films, Inc. This film explains the properties of
      alpha, beta, and gamma rays, cyclotrons, and the contributions of
      various scientists. (Level: junior and senior high school.)


This “Understanding the Atom” series of semi-technical lecture films is
designed for inclusion in a high school senior-level chemistry or
physics course, or it could be used as an introductional unit in nuclear
science at the college level. The films all have sound and are in black
and white.

  _Alpha, Beta, and Gamma_, 44 minutes, 1962.
  _Radiation and Matter_, 44 minutes, 1962.
  _Radiation Detection by Ionization_, 30 minutes, 1962.
  _Radiation Detection by Scintillation_, 30 minutes, 1963.
  _Properties of Radiation_, 30 minutes, 1962.
  _Nuclear Reactions_, 29½ minutes, 1963.
  _Radiological Safety_, 30 minutes, 1963.



                               FOOTNOTES


[1]For more information about these devices, see _Accelerators_, a
    companion booklet in this Understanding the Atom series.

[2]For more information, see _Synthetic Transuranium Elements_, another
    booklet in this series.

[3]The designation ²³⁵U is a new format, now in international usage, for
    the more familiar style, U²³⁵, to designate isotopes.

[4]For more about plutonium, see _Plutonium_, a companion booklet in
    this series.

[5]For more information on reactors, see _Nuclear Reactors_, another
    booklet in this series.



                          Transcriber’s Notes


—Silently corrected a few typos.

—Retained publication information from the printed edition: this eBook
  is public-domain in the country of publication.

—In the text versions only, text in italics is delimited by
  _underscores_.





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