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.
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.
Figure 5 This diagram shows what happens in a chain reaction resulting from fission of uranium-235 atoms.
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.
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.
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.”
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.
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.
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.
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.
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.
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.
IN MEDICINE: Iodine-131 reveals spread of thyroid cancer in patient’s body.
IN SPACE: Plutonium-238 is the
fuel for the atomic generator
powering this TRANSIT satellite.
Courtesy The Martin Company
IN FOOD PRESERVATION: Potatoes stored for 18 months at 47°F. Potato at right had been irradiated, that on left had not.
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.
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.)
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.
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.
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
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.
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.
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.