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<ANTIMG id="coverpage" src="images/cover.jpg" alt="Our Atomic World" width-obs="1000" height-obs="1592" /></div>
<div class="box">
<h1>OUR ATOMIC WORLD</h1>
<p class="center"><span class="ss">by C. Jackson Craven</span></p>
<p class="tbcenter"><span class="ss large">THE STORY OF ATOMIC ENERGY</span></p>
<p class="tbcenter"><span class="ss">U.S. ATOMIC ENERGY COMMISSION
<br/>Division of Technical Information</span>
<br/><i>Understanding the Atom Series</i></p>
</div>
<div class="pb" id="Page_i">i</div>
<h2><span class="small">The Understanding the Atom Series</span></h2>
<p>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.</p>
<p>The United States Atomic Energy Commission provides
this booklet to help you achieve such understanding.</p>
<p class="jr1"><ANTIMG class="inline" src="images/ejb.jpg" alt="Edward J. Brunenkant" width-obs="300" height-obs="98" />
<br/>Edward J. Brunenkant, Director
<br/>Division of Technical Information</p>
<div class="verse">
<p class="t0"><span class="ss">UNITED STATES ATOMIC ENERGY COMMISSION</span></p>
</div>
<div class="verse">
<p class="t0"><span class="ssn">Dr. Glenn T. Seaborg, Chairman</span></p>
<p class="t0"><span class="ssn">James T. Ramey</span></p>
<p class="t0"><span class="ssn">Wilfrid E. Johnson</span></p>
<p class="t0"><span class="ssn">Dr. Theos J. Thompson</span></p>
<p class="t0"><span class="ssn">Dr. Clarence E. Larson</span></p>
</div>
<div class="pb" id="Page_ii">ii</div>
<h1 title="">OUR ATOMIC WORLD</h1>
<p class="center"><span class="ss">by C. Jackson Craven</span></p>
<h2 id="toc" class="center">CONTENTS</h2>
<br/><SPAN href="#c1">THE GREEKS WERE CURIOUS ABOUT MATTER</SPAN> 1
<br/><SPAN href="#c2">THE ATOMIC THEORY IS CONFIRMED</SPAN> 2
<br/><SPAN href="#c3">CATHODE RAYS SHOW ATOMS CONTAIN SMALLER PARTS</SPAN> 3
<br/><SPAN href="#c4">RADIOACTIVE ATOMS DISCOVERED</SPAN> 5
<br/><SPAN href="#c5">RUTHERFORD FINDS THE ATOMIC NUCLEUS</SPAN> 6
<br/><SPAN href="#c6">THE PROTON IS RECOGNIZED</SPAN> 8
<br/><SPAN href="#c7">ISOTOPES ARE DISCOVERED</SPAN> 9
<br/><SPAN href="#c8">THE ALCHEMISTS’ DREAM COMES TRUE</SPAN> 10
<br/><SPAN href="#c9">SOME PARTICLES HAVE NO ELECTRIC CHARGE</SPAN> 13
<br/><SPAN href="#c10">MATTER IS ENERGY; ENERGY IS MATTER</SPAN> 14
<br/><SPAN href="#c11">NUCLEI CONTAIN ENERGY</SPAN> 15
<br/><SPAN href="#c12">CHRONOLOGY</SPAN> 18
<br/><SPAN href="#c13">FISSION IS EXPLAINED</SPAN> 20
<br/><SPAN href="#c14">THE FISSION BOMB IS EXPLODED</SPAN> 23
<br/><SPAN href="#c15">NUCLEAR ENERGY IS NEEDED FOR THE FUTURE</SPAN> 25
<br/><SPAN href="#c16">FUSION HAS POTENTIAL</SPAN> 26
<br/><SPAN href="#c17">ISOTOPES HAVE MANY USES</SPAN> 29
<br/><SPAN href="#c18">RADIOISOTOPES AT WORK</SPAN> 30
<br/><SPAN href="#c19">THE ATOMIC ENERGY COMMISSION</SPAN> 31
<br/><SPAN href="#c20">TOWARD AN INTERNATIONAL ATOM</SPAN> 33
<br/><SPAN href="#c21">SUGGESTED REFERENCES</SPAN> 35
<p class="tbcenter"><span class="ss">United States Atomic Energy Commission</span>
<br/><span class="ss">Division of Technical Information</span>
<br/><span class="small">Library of Congress Catalog Card Number: 63-64918</span>
<br/><span class="small">1963; 1964 (Rev.)</span></p>
<div class="pb" id="Page_iii">iii</div>
<div class="fig"> id="imgx1"> <ANTIMG src="images/p02.jpg" alt="" width-obs="401" height-obs="600" /> <p class="pcap">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.
<br/><span class="smaller">Courtesy Union Carbide Corporation</span></p>
</div>
<p><span class="ss">C. JACKSON CRAVEN</span> 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.</p>
<p>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.</p>
<p>His research interests include infrared spectroscopy, gaseous
diffusion through porous media, and the physical properties of
fibers.</p>
<div class="pb" id="Page_1">1</div>
<h1 title="">OUR ATOMIC WORLD</h1>
<p class="center">By C. Jackson Craven</p>
<blockquote>
<p><i>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.</i></p>
</blockquote>
<h2 id="c1"><span class="small">The Greeks Were Curious About Matter</span></h2>
<p>Certain philosophers of ancient Greece—Democritus for
one—were fascinated by the question: <i>what is matter?</i> You
can imagine one of the philosophers saying to his pupils:</p>
<p>“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 <i>think</i> 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?”</p>
<p>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.</p>
<div class="pb" id="Page_2">2</div>
<p>This concept was humorously expressed by the British
mathematician Augustus De Morgan (1806-1871) in these
lines:</p>
<div class="verse">
<p class="t0"><i>Great fleas have little fleas upon their backs to bite ’em,</i></p>
<p class="t0"><i>And little fleas have lesser fleas, and so, ad infinitum.</i></p>
</div>
<h2 id="c2"><span class="small">The Atomic Theory Is Confirmed</span></h2>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<p>These principles of chemical combination convinced
Dalton that each chemical element consists of small,
<span class="pb" id="Page_3">3</span>
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 <i>times</i> heavier or lighter it was than an atom of
another element.</p>
<p>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.</p>
<h2 id="c3"><span class="small">Cathode Rays Show Atoms Contain Smaller Parts</span></h2>
<p>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.</p>
<p>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 <SPAN href="#fig1">Figure 1</SPAN>.</p>
<p>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.”</p>
<div class="pb" id="Page_4">4</div>
<div class="fig"> id="fig1"> <ANTIMG src="images/p03.jpg" alt="" width-obs="1000" height-obs="475" /> <p class="pcap"><b>Figure 1</b> <i>Geissler Tube.</i></p> </div>
<dl class="undent pcap"><br/>CURRENT SOURCE
<br/>CATHODE (-)
<br/>STREAM OF ELECTRONS
<br/>VACUUM PUMP
<br/>ANODE (+)
<p>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.</p>
<p>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.</p>
<div class="pb" id="Page_5">5</div>
<p>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.</p>
<h2 id="c4"><span class="small">Radioactive Atoms Discovered</span></h2>
<div class="fig"> id="imgx2"> <ANTIMG src="images/p03a.jpg" alt="" width-obs="504" height-obs="608" /> <p class="pcap"><i>Henri Becquerel</i> <br/><span class="smaller">Courtesy Journal of Chemical Education, <span class="u">Discovery of the Elements</span>, Mary Elvira Weeks.</span></p> </div>
<p>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.</p>
<p>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.</p>
<div class="pb" id="Page_6">6</div>
<h2 id="c5"><span class="small">Rutherford Finds the Atomic Nucleus</span></h2>
<div class="fig"> id="imgx3"> <ANTIMG src="images/p04.jpg" alt="" width-obs="466" height-obs="599" /> <p class="pcap"><i>Ernest Rutherford, 1871-1937</i> <br/><span class="smaller">Courtesy Nobelstiftelsen</span></p>
</div>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<p>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
<span class="pb" id="Page_7">7</span>
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 <i>stable</i>
atom is produced. The end product in this “decay” process
in naturally occurring radioactive elements is lead.</p>
<p>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 <SPAN href="#fig2">Figure 2</SPAN>.)</p>
<div class="fig"> id="fig2"> <ANTIMG src="images/p04a.jpg" alt="" width-obs="800" height-obs="408" /> <p class="pcap"><b>Figure 2</b> <i>Rutherford’s most famous experiment, which led him to the concept of the nucleus.</i></p> </div>
<p>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.
<span class="pb" id="Page_8">8</span>
(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.</p>
<p>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!</p>
<h2 id="c6"><span class="small">The Proton Is Recognized</span></h2>
<p>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.”</p>
<div class="pb" id="Page_9">9</div>
<h2 id="c7"><span class="small">Isotopes Are Discovered</span></h2>
<p>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.</p>
<p>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.</p>
<p>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 <i>same place</i> on the periodic chart of the elements.
Soddy suggested that such atoms be called <i>isotopes</i>,
from a Greek word meaning “same place.”</p>
<p>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
<span class="pb" id="Page_10">10</span>
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.</p>
<p>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 <SPAN href="#fig3">Figure 3</SPAN>.) 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!</p>
<div class="fig"> id="fig3"> <ANTIMG src="images/p05.jpg" alt="" width-obs="800" height-obs="519" /> <p class="pcap"><b>Figure 3</b> <i>Mass spectrograph as used by Thomson and Aston to measure the atomic weight of neon.</i></p> </div>
<dl class="undent pcap"><br/>NEON 20
<br/>NEON 22
<h2 id="c8"><span class="small">The Alchemists’ Dream Comes True</span></h2>
<p>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
<span class="pb" id="Page_11">11</span>
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.”</p>
<div class="fig"> id="imgx4"> <ANTIMG src="images/p05a.jpg" alt="" width-obs="407" height-obs="600" /> <p class="pcap"><i>Medieval Alchemist</i> <br/><span class="smaller">Courtesy Fisher Scientific Company</span></p> </div>
<p>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:</p>
<p>“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.”</p>
<div class="pb" id="Page_12">12</div>
<p>This prediction has certainly been verified through the
use of the atomic artillery provided by extremely powerful
particle accelerators, or “atom smashers.”<SPAN class="fn" id="fr_1" href="#fn_1">[1]</SPAN></p>
<div class="fig"> id="imgx5"> <ANTIMG src="images/p06.jpg" alt="" width-obs="1000" height-obs="605" /> <p class="pcap"><i>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.</i>
<br/><span class="smaller">Courtesy Lawrence Radiation Laboratory</span></p>
</div>
<p>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.</p>
<div class="pb" id="Page_13">13</div>
<h2 id="c9"><span class="small">Some Particles Have No Electric Charge</span></h2>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<div class="pb" id="Page_14">14</div>
<h2 id="c10"><span class="small">Matter Is Energy; Energy Is Matter</span></h2>
<p>So far, in the story about man’s curiosity concerning the
fundamental nature and structure of matter, the development
of ideas about <i>structure</i> has been emphasized. We will now
take a brief look at a development which strongly influenced
our ideas about the fundamental <i>nature</i> of matter.</p>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<div class="fig"> id="imgx6"> <ANTIMG src="images/p07.jpg" alt="" width-obs="650" height-obs="800" /> <p class="pcap"><i>Albert Einstein in 1905.</i> <br/><span class="smaller">Courtesy Lotte Jacobi, Hillsboro, New Hampshire</span></p> </div>
<p>One of Einstein’s predictions had to do with the equivalence
of matter and energy. Until 1905 <i>matter</i> had been
considered as something that has mass or inertia; <i>energy</i>,
on the other hand, had been regarded as the ability to do
<span class="pb" id="Page_15">15</span>
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:</p>
<div class="verse">
<p class="lc">E = MC²</p>
</div>
<div class="verse">
<p class="t0">where</p>
<p class="t2">E = quantity of energy,</p>
<p class="t2">M = quantity of matter, and</p>
<p class="t2">C = speed of light in a vacuum.</p>
</div>
<h2 id="c11"><span class="small">Nuclei Contain Energy</span></h2>
<p>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.</p>
<p>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.</p>
<p>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 <SPAN href="#fig4">Figure 4</SPAN>.)</p>
<div class="pb" id="Page_16">16</div>
<div class="fig"> id="fig4"> <ANTIMG src="images/p08.jpg" alt="" width-obs="800" height-obs="727" /> <p class="pcap"><b>Figure 4</b> <i>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.</i></p>
</div>
<dl class="undent pcap"><br/>HELIUM NUCLEUS
<br/>TWO PROTONS AND TWO NEUTRONS
<p>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.</p>
<p>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.</p>
<p>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,
<span class="pb" id="Page_17">17</span>
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.</p>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<div class="fig"> id="imgx7"> <ANTIMG src="images/p08b.jpg" alt="" width-obs="1000" height-obs="382" /> <p class="pcap"><i>The NS</i> Savannah <i>was the first cargo-passenger ship to be driven by nuclear power</i>. <br/><span class="smaller">Courtesy States Marine Lines</span></p>
</div>
<div class="fig"> id="imgx8"> <ANTIMG src="images/p08c.jpg" alt="" width-obs="1000" height-obs="384" /> <p class="pcap"><i>The</i> Nautilus <i>was the Navy’s first atomic-powered submarine</i>. <br/><span class="smaller">Courtesy U. S. Navy</span></p> </div>
<div class="pb" id="Page_18">18</div>
<h2 id="c12"><span class="small">CHRONOLOGY</span></h2>
<table class="center">
<tr><td class="l">1800 </td><td class="l">Dalton firmly establishes atomic theory of matter.</td></tr>
<tr><td class="l">1890-1900 </td><td class="l">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.</td></tr>
<tr><td class="l">1905 </td><td class="l">Einstein postulates the equivalence of mass and energy.</td></tr>
<tr><td class="l">1911 </td><td class="l">Rutherford recognizes nucleus.</td></tr>
<tr><td class="l">1919 </td><td class="l">Rutherford achieves transmutation of one stable chemical element (nitrogen) into another (oxygen).</td></tr>
<tr><td class="l">1920-1925 </td><td class="l">Improved mass spectrographs show that changes in mass per nuclear particle accompanying transmutation account for energy released by nucleus.</td></tr>
<tr><td class="l">1932 </td><td class="l">Chadwick identifies neutrons.</td></tr>
<tr><td class="l">1939 </td><td class="l">Discovery of uranium fission by German scientists.</td></tr>
<tr><td class="l">1940 </td><td class="l">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.</td></tr>
<tr><td class="l">1942 </td><td class="l">Achievement of first self-sustaining nuclear reaction, University of Chicago.</td></tr>
<tr><td class="l">1945 </td><td class="l">First successful test of an atomic device, near Alamagordo, New Mexico, followed by the dropping of atomic bombs on Hiroshima and Nagasaki, Japan.</td></tr>
<tr><td class="l">1946 </td><td class="l">U. S. Atomic Energy Commission established by Act of Congress.</td></tr>
<tr><td class="l"> </td><td class="l">First shipment of radioisotopes from Oak Ridge goes to hospital in St. Louis, Missouri.</td></tr>
<tr class="pbtr"><td colspan="2">
<span class="pb" id="Page_19">19</span>
</td></tr>
<tr><td class="l">1951 </td><td class="l">First significant amount of electricity (100 kilowatts) produced from atomic energy at testing station in Idaho.</td></tr>
<tr><td class="l">1952 </td><td class="l">First detonation of a thermonuclear bomb, Eniwetok Atoll, Pacific Ocean.</td></tr>
<tr><td class="l">1953 </td><td class="l">President Eisenhower announces U. S. Atoms-for-Peace program and proposes establishment of an international atomic energy agency.</td></tr>
<tr><td class="l">1954 </td><td class="l">First nuclear-powered submarine, <i>Nautilus</i>, commissioned.</td></tr>
<tr><td class="l">1955 </td><td class="l">First United Nations International Conference on Peaceful Uses of Atomic Energy held in Geneva, Switzerland.</td></tr>
<tr><td class="l">1957 </td><td class="l">First commercial use of power from a civilian reactor takes place in California.</td></tr>
<tr><td class="l"> </td><td class="l">Shippingport Atomic Power Plant in Pennsylvania reaches full power of 60,000 kilowatts.</td></tr>
<tr><td class="l"> </td><td class="l">International Atomic Energy Agency formally established.</td></tr>
<tr><td class="l">1959 </td><td class="l">First nuclear-powered merchant ship, the <i>Savannah</i>, launched at Camden, New Jersey.</td></tr>
<tr><td class="l"> </td><td class="l">Commissioning of first nuclear-powered Polaris missile-launching submarine <i>George Washington</i>.</td></tr>
<tr><td class="l">1961 </td><td class="l">A radioisotope-powered electric power generator placed in orbit, the first use of nuclear power in space.</td></tr>
<tr><td class="l">1962 </td><td class="l">Nuclear power plant in the Antarctic becomes operational.</td></tr>
<tr><td class="l">1963 </td><td class="l">President Kennedy ratified the Limited Test Ban Treaty for the United States on October 7.</td></tr>
<tr><td class="l">1964 </td><td class="l">President Johnson signed law permitting private ownership of certain nuclear materials.</td></tr>
</table>
<div class="pb" id="Page_20">20</div>
<h2 id="c13"><span class="small">Fission is Explained</span></h2>
<div class="fig"> id="imgx9"> <ANTIMG src="images/p09.jpg" alt="" width-obs="543" height-obs="600" /> <p class="pcap"><i>Enrico Fermi 1901-1954</i> <br/><span class="smaller">Courtesy Chemical and Engineering News</span></p>
</div>
<p>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.</p>
<p>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.”</p>
<p>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.<SPAN class="fn" id="fr_2" href="#fn_2">[2]</SPAN></p>
<div class="pb" id="Page_21">21</div>
<p>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 <i>fission</i>, of
the nucleus into two parts with separate weights that place
them somewhere near the middle of the periodic table.</p>
<div class="fig"> id="imgx10"> <ANTIMG src="images/p09a.jpg" alt="" width-obs="800" height-obs="671" /> <p class="pcap"><i>Lise Meitner and Otto Hahn in their laboratory in the 1930s.</i> <br/><span class="smaller">Courtesy Addison-Wesley Publishing Co.</span></p>
</div>
<p>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.</p>
<div class="fig"> id="imgx11"> <ANTIMG src="images/p09c.jpg" alt="" width-obs="1000" height-obs="658" /> <p class="pcap"><i>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.</i></p>
</div>
<p>The excitement among physicists became even greater
when it was realized that this newly discovered process of
<span class="pb" id="Page_22">22</span>
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 <SPAN href="#fig5">Figure 5</SPAN>.
(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.</p>
<div class="fig"> id="fig5"> <ANTIMG src="images/p10.jpg" alt="" width-obs="959" height-obs="1000" /> <p class="pcap"><b>Figure 5</b> <i>This diagram shows what happens in a chain reaction resulting
from fission of uranium-235
atoms.</i></p>
</div>
<dl class="undent pcap"><br/>STRAY NEUTRON
<br/>²³⁵U
<br/><b>ORIGINAL FISSION</b>
<br/>FISSION FRAGMENTS
<br/>One to three neutrons from fission process
<br/>A NEUTRON SOMETIMES LOST
<br/>²³⁸U
<br/>CHANGES TO PLUTONIUM
<br/>²³⁵U
<br/><b>ONE NEW FISSION</b>
<br/>FISSION FRAGMENT
<br/>One to three neutrons again
<br/>²³⁵U
<br/>²³⁵U
<br/><b>TWO NEW FISSIONS</b>
<br/>FISSION FRAGMENTS
<div class="pb" id="Page_23">23</div>
<h2 id="c14"><span class="small">The Fission Bomb Is Exploded</span></h2>
<p>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.</p>
<p>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.</p>
<p>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.<SPAN class="fn" id="fr_3" href="#fn_3">[3]</SPAN> 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.</p>
<p>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.</p>
<p>For this operation an enormous plant containing a very
large barrier area, miles of piping, and countless pumps
was built at Oak Ridge, Tennessee.</p>
<div class="pb" id="Page_24">24</div>
<p>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.</p>
<p>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.<SPAN class="fn" id="fr_4" href="#fn_4">[4]</SPAN> 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.</p>
<p>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 <i>reactors</i>, were
rushed to completion near the
Columbia River at Hanford,
Washington, to make plutonium.</p>
<div class="fig"> id="imgx12"> <ANTIMG src="images/p11.jpg" alt="" width-obs="800" height-obs="463" /> <p class="pcap"><i>First atomic bomb explosion at Alamagordo, New Mexico, at 5:30 a.m. on July 16, 1945.</i>
<br/><span class="smaller">Courtesy U. S. Army</span></p>
</div>
<p>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
<span class="pb" id="Page_25">25</span>
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.</p>
<p>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.</p>
<h2 id="c15"><span class="small">Nuclear Energy Is Needed for the Future</span></h2>
<p>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.”</p>
<div class="fig"> id="imgx13"> <ANTIMG src="images/p11a.jpg" alt="" width-obs="800" height-obs="890" /> <p class="pcap"><i>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.</i>
<br/><span class="smaller">Courtesy Westinghouse Electric Corporation</span></p>
</div>
<p>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.<SPAN class="fn" id="fr_5" href="#fn_5">[5]</SPAN></p>
<div class="pb" id="Page_26">26</div>
<p>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.</p>
<h2 id="c16"><span class="small">Fusion Has Potential</span></h2>
<p>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.</p>
<p>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.</p>
<p>The principle illustrated by <SPAN href="#fig4">Figure 4</SPAN> 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.</p>
<p>The accompanying loss of weight per particle indicated
by <SPAN href="#fig4">Figure 4</SPAN> 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
<span class="pb" id="Page_27">27</span>
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.</p>
<div class="fig"> id="imgx14"> <ANTIMG src="images/p12.jpg" alt="" width-obs="658" height-obs="800" /> <p class="pcap"><i>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.</i>
<br/><span class="smaller">Courtesy Sacramento Peak Observatory, AFCRL</span></p>
</div>
<p>Since fusion of light nuclei is produced by extremely high
temperatures, fusion events are called <i>thermonuclear reactions</i>.
The possibility of bringing about thermonuclear reactions
on earth to serve as a source of energy has naturally
attracted much attention.</p>
<p>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.</p>
<div class="fig"> id="imgx15"> <ANTIMG src="images/p12a.jpg" alt="" width-obs="800" height-obs="707" /> <p class="pcap"><i>An early phase of a nuclear detonation at Eniwetok Atoll during the 1951 tests.</i>
<br/><span class="smaller">Courtesy Joint Task Force Three</span></p>
</div>
<p>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
<span class="pb" id="Page_28">28</span>
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.</p>
<p>At such extreme temperatures
all atoms are stripped
of electrons; the resulting
mixture of nuclei and free
electrons is called a <i>plasma</i>.
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.</p>
<div class="fig"> id="imgx16"> <ANTIMG src="images/p13.jpg" alt="" width-obs="598" height-obs="800" /> <p class="pcap"><i>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.</i>
<br/><span class="smaller">Courtesy General Atomic Division, General Dynamics Corporation</span></p>
</div>
<p>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.</p>
<div class="pb" id="Page_29">29</div>
<p>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.</p>
<h2 id="c17"><span class="small">Isotopes Have Many Uses</span></h2>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<div class="pb" id="Page_30">30</div>
<h2 id="c18"><span class="small">Radioisotopes at Work</span></h2>
<div class="fig"> id="imgx17"> <ANTIMG src="images/p14.jpg" alt="" width-obs="609" height-obs="800" /> <p class="pcap"><b>IN MEDICINE:</b> <i>Iodine-131 reveals spread of thyroid cancer in patient’s body.</i></p>
</div>
<div class="fig"> id="imgx18"> <ANTIMG src="images/p14c.jpg" alt="" width-obs="796" height-obs="786" /> <p class="pcap"><b>IN SPACE:</b> <i>Plutonium-238 is the fuel for the atomic generator powering this TRANSIT satellite.</i>
<br/><span class="smaller">Courtesy The Martin Company</span></p>
</div>
<div class="fig"> id="imgx19"> <ANTIMG src="images/p14d.jpg" alt="" width-obs="800" height-obs="562" /> <p class="pcap"><b>IN FOOD PRESERVATION:</b> <i>Potatoes stored for 18 months at 47°F. Potato at right had been irradiated, that on left had not.</i></p>
</div>
<div class="fig"> id="imgx20"> <ANTIMG src="images/p14e.jpg" alt="" width-obs="382" height-obs="801" /> <p class="pcap"><b>IN INDUSTRY:</b> <i>Radioactive iridium was used to inspect the hull of the carrier</i> Independence.
<br/><span class="smaller">Courtesy Technical Operations, Inc.</span></p>
</div>
<div class="pb" id="Page_31">31</div>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<h2 id="c19"><span class="small">The Atomic Energy Commission</span></h2>
<p>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
<span class="pb" id="Page_32">32</span>
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.)</p>
<div class="fig"> id="imgx21"> <ANTIMG src="images/p15.jpg" alt="" width-obs="1000" height-obs="741" /> <p class="pcap"><i>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.</i>
<br/><span class="smaller">Courtesy United Press International</span></p>
</div>
<p>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.</p>
<div class="pb" id="Page_33">33</div>
<h2 id="c20"><span class="small">Toward an International Atom</span></h2>
<p>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.</p>
<div class="fig"> id="imgx22"> <ANTIMG src="images/p15a.jpg" alt="" width-obs="1000" height-obs="660" /> <p class="pcap"><i>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.</i>
<br/><span class="smaller">Courtesy United Nations</span></p>
</div>
<div class="pb" id="Page_34">34</div>
<div class="fig"> id="imgx23"> <ANTIMG src="images/p16.jpg" alt="" width-obs="1000" height-obs="784" /> <p class="pcap"><i>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.</i></p>
</div>
<p>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.</p>
<p>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.</p>
<div class="pb" id="Page_35">35</div>
<h2 id="c21"><span class="small">Suggested References</span></h2>
<h3 id="c22">Books</h3>
<p class="revint"><i>Atomic Energy</i>, Irene D. Jaworski and Alexander Joseph, Harcourt,
Brace and World, Inc., New York 10017, 1961, 218 pp., $4.95.</p>
<p class="revint"><i>Atompower</i>, Joseph M. Dukert, Coward-McCann, Inc., New York
10016, 1962, 127 pp., $3.50.</p>
<p class="revint"><i>Atoms Today and Tomorrow</i> (revised edition), Margaret O. Hyde,
McGraw-Hill Book Company, New York 10036, 1966, 160 pp.,
$3.25.</p>
<p class="revint"><i>Basic Laws of Matter</i> (revised edition), Harrie S. W. Massey and
Arthur R. Quinton, Herald Books, Bronxville, New York 10710,
1965, 178 pp., $3.75.</p>
<p class="revint"><i>Building Blocks of the Universe</i> (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.</p>
<p class="revint"><i>Elements of the Universe</i>, 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).</p>
<p class="revint"><i>Inside the Atom</i> (revised edition), Isaac Asimov, Abelard-Schuman,
Ltd., New York 10019, 1966, 197 pp., $4.00.</p>
<p class="revint"><i>Introducing the Atom</i>, Roslyn Leeds, Harper and Row, Publishers,
New York 10016, 1967, 224 pp., $3.95.</p>
<p class="revint"><i>Peacetime Uses of Atomic Energy</i> (revised edition), Martin Mann,
The Viking Press, New York 10022, 1961, 191 pp., $5.00 (hardback);
$1.65 (paperback).</p>
<p class="revint"><i>The Useful Atom</i>, William R. Anderson and Vernon Pizer, The
World Publishing Company, Cleveland, Ohio 44102, 1966, 185 pp.,
$5.75.</p>
<p class="revint"><i>Secret of the Mysterious Rays: The Discovery of Nuclear Energy</i>,
Vivian Grey, Basic Books, Inc., Publishers, New York 10016,
1966, 120 pp., $3.95.</p>
<p class="revint"><i>The Heart of the Atom: The Structure of the Atomic Nucleus</i>,
Bernard L. Cohen, Doubleday and Company, Inc., New York
10017, 1967, 120 pp., $3.95 (hardback); $1.25 (paperback).</p>
<p class="revint"><i>The Questioners: Physicists and the Quantum Theory</i>, Barbara L.
Cline, Thomas Y. Crowell Company, New York 10003, 1965,
274 pp., $5.00.</p>
<p class="revint"><i>The Atom and Its Nucleus</i>, George Gamow, Prentice-Hall, Inc.,
Englewood Cliffs, New Jersey 07632, 1961, 153 pp., $1.95.</p>
<p class="revint"><i>The Atomic Energy Deskbook</i>, John F. Hogerton, Reinhold Publishing
Corporation, New York 10022, 1963, 673 pp., $11.00.</p>
<p class="revint"><i>Atomic Energy Encyclopedia in the Life Sciences</i>, Charles W.
Shilling (Ed.), W. B. Saunders Company, Philadelphia, Pennsylvania
19105, 1964, 474 pp., $10.50.</p>
<p class="revint"><i>Atoms for Peace</i> (revised edition), David O. Woodbury, Dodd,
Mead and Company, New York 10016, 1965, 275 pp., $4.50.</p>
<p class="revint"><i>Manhattan Project</i>, Stephane Groueff, Little, Brown and Company,
Boston, Massachusetts 02106, 1967, 372 pp., $6.95.</p>
<div class="pb" id="Page_36">36</div>
<p class="revint"><i>The New World, 1939/1946</i>, 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.</p>
<p class="revint"><i>Sourcebook on Atomic Energy</i> (third edition), Samuel Glasstone,
D. Van Nostrand Company, Inc., Princeton, New Jersey 08540,
1967, 883 pp., $9.25.</p>
<p class="revint"><i>The World of the Atom</i>, 2 volumes, Henry A. Boorse and Lloyd
Matz (Eds.), Basic Books, Inc., Publishers, New York 10016,
1966, 1873 pp., $35.00.</p>
<h3 id="c23">Motion Pictures</h3>
<p>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.</p>
<p>Each of the following motion pictures explains atomic structure,
fission, and the chain reaction. Additional contents are listed below
with the film.</p>
<p class="revint"><i>A Is for Atom</i>, 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.)</p>
<p class="revint"><i>Atomic Energy</i>, 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.)</p>
<p class="revint"><i>Controlling Atomic Energy</i>, 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.)</p>
<p class="revint"><i>Introducing Atoms and Nuclear Energy</i>, 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.)</p>
<p class="revint"><i>Atomic Physics</i>, 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
<span class="pb" id="Page_37">37</span>
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.)</p>
<p class="revint"><i>Unlocking the Atom</i>, 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.)</p>
<p class="tb">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.</p>
<div class="verse">
<p class="t0"><i>Alpha, Beta, and Gamma</i>, 44 minutes, 1962.</p>
<p class="t0"><i>Radiation and Matter</i>, 44 minutes, 1962.</p>
<p class="t0"><i>Radiation Detection by Ionization</i>, 30 minutes, 1962.</p>
<p class="t0"><i>Radiation Detection by Scintillation</i>, 30 minutes, 1963.</p>
<p class="t0"><i>Properties of Radiation</i>, 30 minutes, 1962.</p>
<p class="t0"><i>Nuclear Reactions</i>, 29½ minutes, 1963.</p>
<p class="t0"><i>Radiological Safety</i>, 30 minutes, 1963.</p>
</div>
<h2 id="c24"><span class="small">FOOTNOTES</span></h2>
<div class="fnblock"><div class="fndef"><SPAN class="fn" id="fn_1" href="#fr_1">[1]</SPAN>For more information about these devices, see <i>Accelerators</i>, a
companion booklet in this Understanding the Atom series.</div>
<div class="fndef"><SPAN class="fn" id="fn_2" href="#fr_2">[2]</SPAN>For more information, see <i>Synthetic Transuranium Elements</i>,
another booklet in this series.</div>
<div class="fndef"><SPAN class="fn" id="fn_3" href="#fr_3">[3]</SPAN>The designation ²³⁵U is a new format, now in international usage,
for the more familiar style, U²³⁵, to designate isotopes.</div>
<div class="fndef"><SPAN class="fn" id="fn_4" href="#fr_4">[4]</SPAN>For more about plutonium, see <i>Plutonium</i>, a companion booklet
in this series.</div>
<div class="fndef"><SPAN class="fn" id="fn_5" href="#fr_5">[5]</SPAN>For more information on reactors, see <i>Nuclear Reactors</i>, another
booklet in this series.</div>
</div>
<h2 id="trnotes">Transcriber’s Notes</h2>
<ul>
<li>Silently corrected a few typos.</li>
<li>Retained publication information from the printed edition: this eBook is public-domain in the country of publication.</li>
<li>In the text versions only, text in italics is delimited by _underscores_.</li>
</ul>
<SPAN name="endofbook"></SPAN>
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