Title: Our Atomic World: The Story of Atomic Energy
Author: C. Jackson Craven
Release date: September 8, 2021 [eBook #66246]
Most recently updated: October 18, 2024
Language: English
Credits: Stephen Hutcheson and the Online Distributed Proofreading Team at https://www.pgdp.net
by C. Jackson Craven
THE STORY OF ATOMIC ENERGY
U.S. ATOMIC ENERGY COMMISSION
Division of Technical Information
Understanding the Atom Series
Nuclear energy is playing a vital role in the life of every man, woman, and child in the United States today. In the years ahead it will affect increasingly all the peoples of the earth. It is essential that all Americans gain an understanding of this vital force if they are to discharge thoughtfully their responsibilities as citizens and if they are to realize fully the myriad benefits that nuclear energy offers them.
The United States Atomic Energy Commission provides this booklet to help you achieve such understanding.
Edward J. Brunenkant
Edward J. Brunenkant, Director
Division of Technical Information
UNITED STATES ATOMIC ENERGY COMMISSION
Dr. Glenn T. Seaborg, Chairman
James T. Ramey
Wilfrid E. Johnson
Dr. Theos J. Thompson
Dr. Clarence E. Larson
by C. Jackson Craven
United States Atomic Energy Commission
Division of Technical Information
Library of Congress Catalog Card Number: 63-64918
1963; 1964 (Rev.)
The cover is a time-exposed photograph
of an animated model of a uranium-235
atom. The center represents the nucleus,
greatly exaggerated in size. The fine
lines represent the electrons whirling
about the nucleus.
Courtesy Union Carbide Corporation
C. JACKSON CRAVEN is a teacher’s teacher as well as a student’s teacher, and has had an active career aiding understanding of atomic energy as a member of the University of Tennessee faculty and on the staff of the Oak Ridge Institute of Nuclear Studies. He has conducted short courses to instruct groups of high school science teachers in nuclear energy, and has served in a key capacity in training Institute demonstration-lecturers who visit high schools throughout the nation.
Dr. Craven worked during World War II for the Manhattan Project, which built the first atomic bomb. He earned bachelor’s and graduate degrees at the University of North Carolina, and later taught physics and mathematics at Delta State Teachers College and at Furman and Emory Universities.
His research interests include infrared spectroscopy, gaseous diffusion through porous media, and the physical properties of fibers.
By C. Jackson Craven
The story of atomic energy evolves from the curiosity of people concerning the nature and structure of matter, the stuff of which all material things are made.
Certain philosophers of ancient Greece—Democritus for one—were fascinated by the question: what is matter? You can imagine one of the philosophers saying to his pupils:
“Gentlemen, let us consider a piece of cheese. With a knife we can cut it in two, thus obtaining smaller pieces. We can then cut one of these smaller pieces in two, obtaining still smaller pieces. We can think about repeating this process over and over to get smaller and smaller pieces of cheese. Now can this process be continued without limit, or will a time come when we arrive at the smallest possible piece of cheese? In other words, is there a piece so small that we must have at least that much or none, with no choice in between?”
It is probable that most people who thought about this question at all during the next two thousand years answered the last question in the negative. The prevailing notion was that matter was continuous, with no theoretical limit as to how small a piece of cheese, or anything else, might be.
This concept was humorously expressed by the British mathematician Augustus De Morgan (1806-1871) in these lines:
Great fleas have little fleas upon their backs to bite ’em,
And little fleas have lesser fleas, and so, ad infinitum.
De Morgan evidently did not keep up with the latest developments in science, however, because two years before his birth, John Dalton, an English schoolteacher, had changed the atomic theory of matter from a philosophical speculation into a firmly established principle. The evidence that convinced Dalton and many other contemporary scientists of the reality of atoms came from quantitative chemical analysis.
Dalton knew that many chemical substances could be separated into two or more simpler substances. Chemicals that could be separated further were called compounds; those that could not were called elements. Careful experiments by Dalton and others showed that whenever two or more elements combined chemically to make a compound the relative amounts of the elements had to be carefully adjusted to fit a definite proportion in order to have no elements left over after the reaction was finished. For example, if hydrogen and oxygen were combined to form water, the weight of oxygen had to be eight times the weight of hydrogen; otherwise, either some hydrogen or some oxygen would be left over.
This fundamental truth is now called the Law of Definite Proportions. Another important principle, called the Law of Multiple Proportions, is illustrated by hydrogen peroxide, which is made up of the same two elements that are found in water. The weight of oxygen in hydrogen peroxide, however, is 16 times the weight of hydrogen or exactly twice the relative weight found in water.
These principles of chemical combination convinced Dalton that each chemical element consists of small, indivisible units, all just alike, called atoms, and that each chemical compound also has basic units, called molecules, which cannot be divided without reducing the compound into its elements—that is, destroying it as a compound. He visualized a molecule of a compound as formed by the uniting of individual atoms of two or more elements. It was obvious to him that in any molecule of a compound, the weight of each atom of a component element bore a proportionate relationship to the weight of the entire molecule which was equal to the proportion, by weight, of all that element in the compound. And although Dalton had no idea how heavy any individual atom really was, he could tell how many times heavier or lighter it was than an atom of another element.
Incidentally, Dalton mistakenly thought that one atom of oxygen was eight times as heavy as one atom of hydrogen instead of 16 times as heavy. He assumed a water molecule to be HO instead of H₂O.
Curiosity about the fundamental nature of matter was matched by equally avid curiosity about the fundamental nature of electricity. Before 1850 much had been learned about the behavior of electric charge and electric currents flowing through solids and liquids. Real progress in understanding electric charge, however, had to wait for the development of highly efficient vacuum pumps.
About 1854 Heinrich Geissler, a German glassblower, developed an improved suction pump, and also succeeded in sealing into a glass tube two wires attached to metal electrodes inside the tube. Experimenters were then able to study the flow of electricity through a near-vacuum. A Geissler tube is diagramed in Figure 1.
By the 1890s it had become clear that the flow of electricity through a highly evacuated tube consisted of a negative electric charge moving at a very high speed along straight lines between sealed-in electrodes. Since it originated at the negative electrode, or cathode, the invisible stream of charge was named “cathode rays.”
Figure 1 Geissler Tube.
Although many investigators contributed to knowledge about cathode rays, the experiments of Joseph J. Thomson, a British physicist, are generally considered to have been the most enlightening. Thomson arranged a cathode-ray tube so that the rays could be deflected by magnets and by electrically charged metal plates. By applying certain well-known principles of physics, he was able to confirm an impression already held by physical chemists, namely, that electric charge, like matter, was “atomized”—the stream of charge consisted of a swarm of very small particles, all alike. He succeeded also in determining that the speed of the particles was about one-tenth the speed of light.
Probably Thomson’s most significant result was determining the ratio of the charge of each little particle to its weight. He was able to do this by measuring the magnetic force required to divert a stream of charged particles. (You can do this experiment yourself with relatively simple equipment.) This charge-to-weight ratio proved to be nearly 2000 times greater than the already known charge-to-weight ratio for a positively charged hydrogen atom, or ion, which until then was thought to be the lightest constituent of matter. It remained to be determined whether charge or weight caused the difference. Further experimentation showed that the charges were approximately the same amount in the two cases. It was therefore proven that the weight of the hydrogen atom, lightest of all the atoms, was nearly 2000 times as great as the weight of one of the little negative particles.
The name “electron” was given to the small negative particles identified by Thomson. Since the electrons had come from the cathode, it was apparent that the atoms in the cathode must contain electrons. Thomson reasoned that electric current in a wire is a stream of electrons passing successively from atom to atom and that the difference between an electrically charged atom and a neutral atom is that the charged one has gained or lost one or more electrons.
Henri Becquerel
Courtesy Journal of Chemical Education, Discovery of the Elements, Mary Elvira Weeks.
In 1896 the French physicist Henri Becquerel was investigating the relation between fluorescence and X rays, a puzzling kind of penetrating radiation discovered a few months earlier by the German, Wilhelm Roentgen. Various chemical compounds fluoresce, or glow, when exposed to ultraviolet rays and other types of radiation. While experimenting with a large number of chemicals, Becquerel discovered, quite by accident, that a compound containing the element uranium can, without being exposed to any kind of radiation, darken a photographic plate completely wrapped in heavy black paper.
Although no one realized it at the time, Becquerel had discovered that atoms of some elements will at random times transform themselves into atoms of a different element by emitting certain extremely high-speed charged particles. Atoms that can do this are said to be radioactive, and it was the radiation from transforming uranium atoms that darkened Becquerel’s photographic plate.
Ernest Rutherford,
1871-1937
Courtesy Nobelstiftelsen
We are greatly indebted to the imagination and experimental skill of the British physicist Ernest Rutherford for the interpretation of radioactivity in terms of the structure of atoms.
Rutherford, born and educated in New Zealand, moved to England to work under Thomson at Cambridge University in 1895. Shortly afterward, Wilhelm Roentgen in Germany discovered X rays, Becquerel in France discovered radioactivity, and Thomson proved the existence of the electron.
During the next few years, curiosity about the fundamental nature of radioactivity led a number of people to do a great deal of work. The element thorium was found to be radioactive, and Marie and Pierre Curie discovered two new elements, polonium and radium, that were also radioactive. The radiation from radioactive materials was found to be of three kinds called alpha rays, beta rays, and gamma rays. Alpha rays were first detected by Rutherford, who later identified them as positively charged helium atoms. Becquerel demonstrated that beta rays, like cathode rays, consist of negatively charged electrons. The highly penetrating gamma rays were proved by Rutherford and E. N. da C. Andrade to be electromagnetic radiation similar to X rays.
Rutherford, in collaboration with the English chemist Frederick Soddy, brought order out of a chaos of puzzling discoveries by establishing the general behavior of radioactive atoms. He determined that certain naturally occurring atoms of high atomic weight can spontaneously emit an alpha or a beta particle and thereby convert themselves into new atoms. These new atoms, being also radioactive, sooner or later convert themselves into still different atoms, and so on. Each time an alpha particle is emitted in this sequence, the new atom is lighter by the weight of the alpha particle, or helium atom. The disintegration process proceeds from stage to stage until at last a stable atom is produced. The end product in this “decay” process in naturally occurring radioactive elements is lead.
One experiment by Rutherford and his co-workers had a most profound effect on the understanding of atomic structure. What they did was to direct a stream of alpha particles at a thin piece of gold foil. The results were astonishing. Almost all the particles passed straight through the foil without changing direction. Of the few particles that did ricochet in new directions, however, some were deflected at very sharp angles. (See Figure 2.)
Figure 2 Rutherford’s most famous experiment, which led him to the concept of the nucleus.
As a result of this experiment, Rutherford proposed a concept of the atom entirely different from the one which prevailed at this time. The prevailing notion was one advanced by Thomson which conceived of an atom as a blob of positive electric charge in which were imbedded, in much the same way as plums are in a pudding, enough electrons to neutralize the positive charge. Rutherford’s concept, which quickly set aside Thomson’s “plum pudding” model, was that an atom has all of its positive charge and virtually all of its mass concentrated in a tiny space at its center. (Collisions with this center, which came to be known thereafter as the nucleus, had been responsible for the sharp changes in direction of some of the alpha particles.) The space surrounding this nucleus is entirely empty except for the presence of a number of electrons (79 in the case of the gold atom), each about the same size as the nucleus.
To illustrate Rutherford’s concept, let us imagine a gold atom magnified so that it is as large as a bale of cotton. The nucleus at the center of this large atom would be the size of a speck of black pepper. If this imaginary bale weighed 500 pounds, the little speck at its center would weigh 499¾ pounds; the surrounding cotton (corresponding to empty space in Rutherford’s concept) containing the 79 electrons would weigh but ¼ pound. To express this idea another way, any object such as a gold ring, as dense and solid as it may seem to us, consists almost entirely of nothing!
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.”
At a historic meeting of the British Association for the Advancement of Science held in Birmingham, England, in 1913, two apparently unrelated lines of investigation were reported, each of which showed that some atomic nuclei have identical electric charges but different weights.
One report was presented by Frederick Soddy, who had collaborated with Rutherford in explaining the pattern of natural radioactivity. Soddy knew that the nucleus of a radioactive atom loses both weight and positive charge when it throws out an alpha particle (helium nucleus). On the other hand, when a nucleus emits a beta particle (negative electron), its positive charge increases, but its weight is practically unchanged. Thus Soddy could deduce the weights and nuclear charges of many radioactive products. In several cases the products of two different kinds of radioactivity had the same nuclear charge but different weights. Since it is the positive charge carried by the nucleus of an atom which fixes the number of negative electrons needed to complete the atom, the nuclear charge is really responsible for the exterior appearance, or chemical properties, of the atom.
This conclusion was confirmed by unsuccessful efforts to separate by chemical means different radioactive products having the same nuclear charge but different weights. The products might have had quite different rates of radioactive disintegration, but they appeared to consist of chemically identical atoms of the same chemical element and hence to belong at the same place on the periodic chart of the elements. Soddy suggested that such atoms be called isotopes, from a Greek word meaning “same place.”
At the same meeting, Francis W. Aston, an assistant of Thomson, described what happened when charged atoms, or ions, of neon gas were accelerated in a discharge tube similar to the cathode-ray tube in which Thomson had discovered the electron. The rapidly moving neon ions were deflected by a magnet. Since light objects are more easily deflected than heavy objects, the amount of deflection indicated the weight. By making a comparison with a familiar gas like oxygen, Thomson and Aston were actually able to measure the atomic weight of neon. To their surprise they found two kinds of neon. About nine-tenths of the neon atoms had an atomic weight of 20, and the remainder an atomic weight of 22.
What Thomson and Aston had done was to show that the stable element neon is a mixture of two isotopes. A device that can do what their apparatus did is called a mass spectrograph. (See Figure 3.) Since their time, instruments of this type have shown that more than three-fourths of the stable chemical elements are mixtures of two or more stable isotopes; in fact, there are about 300 such isotopes in all. The number of known unstable radioactive isotopes (radioisotopes), natural or man-made, is greater than 1000 and is still growing!
Figure 3 Mass spectrograph as used by Thomson and Aston to measure the atomic weight of neon.
During the Middle Ages the desire to find a way to convert a base metal like lead into gold was the outstanding incentive for research in chemistry. When the important role of the nucleus in determining the chemical properties of an atom became clear and the natural transmutation accompanying radioactivity was understood, the fascinating idea occurred to many people that perhaps man would soon be able to alter the nucleus of a stable atom and thus deliberately convert one element into another. In a historic lecture delivered in Washington, D. C., in April 1914, Rutherford said, “It is possible that the nucleus of an atom may be altered by direct collision of the nucleus with very swift electrons or atoms of helium (i.e., beta or alpha particles) such as are ejected from radioactive matter.... Under favorable conditions, these particles must pass very close to the nucleus and may either lead to a disruption of the nucleus or to a combination with it.”
Medieval Alchemist
Courtesy Fisher Scientific Company
World War I began shortly after Rutherford made this statement, and preoccupation with war work stopped his experiments with nuclei. In 1919, however, he published a paper describing what happens when alpha particles pass through nitrogen gas. Very fast protons, or hydrogen nuclei, appear to originate along the paths of the alpha particles. The following is from Rutherford’s paper:
“If this be the case, we must conclude that the nitrogen atom is disintegrated under the intense forces developed in a close collision with a swift alpha particle, and that the hydrogen atom which is liberated formed a constituent part of the nitrogen nucleus.... The results as a whole suggest that, if alpha particles or similar projectiles of still greater energy were available for experiment, we might expect to break down the nuclear structure of many of the lighter atoms.”
This prediction has certainly been verified through the use of the atomic artillery provided by extremely powerful particle accelerators, or “atom smashers.”[1]
The Bevatron accelerator at the University of California’s Lawrence
Radiation Laboratory, Berkeley, California, shown after
recent remodeling in which it was enclosed in concrete shielding.
Courtesy Lawrence Radiation Laboratory
Patrick Blackett in England and W. D. Harkins in the United States soon proved independently that, during the nuclear event reported by Rutherford in his 1919 paper, an alpha particle combines with a nitrogen nucleus and that the resulting unstable combination immediately emits a proton and ends up as one of the isotopes of oxygen. This was the first instance of deliberate transmutation of one stable chemical element into another. Since that time practically every known element has been transmuted by bombardment. The dream of the alchemists has been partially fulfilled in that mercury has been changed into gold. We say “partially fulfilled” because the process is much too expensive to be economically profitable.
During the early 1920s a number of investigators, including Harkins in the United States, Orme Masson in Australia, and Rutherford and his assistant James Chadwick in England, seriously considered the possibility that a neutral particle might exist in nature, possibly formed by the very close association of a proton and an electron. However, strenuous efforts to produce such particles by combining protons and electrons were unsuccessful.
During these years the new technique of bombarding all kinds of matter with alpha particles to see what would happen was widely exploited, and it gradually became clear that in a few instances a peculiar and highly penetrating kind of radiation was produced. In 1932, Chadwick succeeded in showing that the peculiar radiation must consist of a stream of particles, each weighing about the same as a proton but having no electrical charge.
The name “neutron” for a possible neutral particle of this type was suggested by Harkins in the United States in 1921. Much evidence now exists that the neutron is a fundamental particle in its own right and that it should not be thought of merely as a particle formed by a very close association between a proton and an electron.
The new particle discovered by Chadwick was destined to play a totally unexpected role, not only in the history of atomic science but also in the fate of nations. It immediately outmoded a previous concept of the nucleus that pictured it as a cluster of protons approximately half of which were neutralized by electrons crowded into the nucleus. A nucleus is now thought of as containing just protons and neutrons.
The neutron was also greeted by nuclear workers as a practically perfect kind of bullet. Unlike charged alpha particles, uncharged neutrons can approach a charged nucleus completely unopposed. It is physically impossible for any kind of container to hold a swarm of free neutrons; they seep right through its walls.
So far, in the story about man’s curiosity concerning the fundamental nature and structure of matter, the development of ideas about structure has been emphasized. We will now take a brief look at a development which strongly influenced our ideas about the fundamental nature of matter.
In 1887 reports appeared on a famous study, often referred to as the Michelson-Morley experiment, which was aimed at determining the earth’s speed through absolute space. The entirely unexpected results of the experiment had a great impact on the concepts of space and time. We will here concern ourselves with just one outcome of the experiment.
In 1905, a young German-born physics student named Albert Einstein, who was working as a patent examiner in Switzerland, published three papers, each of which had a profound effect on a different field of physics.
One of the papers dealt with some peculiar speculations about space and time which began to interest him when he was studying the Michelson-Morley experiment. The contents of the paper are now referred to as the Special Theory of Relativity. This paper contains several predictions that seemed incredible to the average physicist of that day. These predictions have, however, long since been proved valid.
Albert Einstein in 1905.
Courtesy Lotte Jacobi, Hillsboro, New Hampshire
One of Einstein’s predictions had to do with the equivalence of matter and energy. Until 1905 matter had been considered as something that has mass or inertia; energy, on the other hand, had been regarded as the ability to do work. It was believed that the two were as different from each other as, say, a square yard is different from an hour. Einstein’s theory, however, implies that matter and energy are merely two different manifestations of the same fundamental physical reality, and that each may be converted into the other according to the famous equation:
E = MC²
where
E = quantity of energy,
M = quantity of matter, and
C = speed of light in a vacuum.
One more piece of information must be fitted into the story of the atom before it becomes clear why some people began to realize during the 1920s that atomic nuclei contain vast stores of energy that might some day revolutionize civilization. This last item has to do with a nuclear phenomenon known as the packing fraction.
Since any nucleus consists of a certain number of protons and neutrons, it seems logical that the total weight of the nucleus could be determined by adding together the individual weights of the particles in it. When mass spectrographs of sufficiently high accuracy became available, however, it was found that in the case of nuclear weights, the whole was not equal to the sum of its parts! All nuclei (except hydrogen) weigh less than the sum of the weights of the particles in them.
For example, the atomic weight of a proton is 1.00812 and that of a neutron is 1.00893. (These are relative weights based on an internationally accepted scale.) It would seem then that a nucleus of helium containing two protons and two neutrons should have an atomic weight of 2 × 1.00812 plus 2 × 1.00893 or 4.0341. Actually the atomic weight of helium as measured by the mass spectrograph is only 4.0039. (See Figure 4.)
Figure 4 A case where the whole is not equal to the sum of its parts. Two protons and two neutrons are distinctly heavier than a helium nucleus, which also consists of two protons and two neutrons. Energy makes up the difference.
What happens to the missing atomic weight of 0.0302? Physicists now realize that, as postulated in Einstein’s formula, it must be converted into energy! The conversion occurs when the protons and neutrons are drawn together into a helium nucleus by the powerful nuclear forces between them.
When the missing atomic weight 0.0302 is multiplied by the square of the velocity of light according to Einstein’s theory, it is found to represent a tremendous amount of energy. Indeed, the energy released in forming a helium nucleus from two protons and two neutrons turns out to be seven million times that released when a carbon atom combines with an oxygen molecule to produce a molecule of carbon dioxide in the familiar process of combustion.
The general behavior of such losses in atomic weight for atoms throughout the periodic table had been determined as early as 1927, largely through the work of Aston, the English scientist who developed the first mass spectrograph. His results show that, in general, if two light nuclei combine to form a heavier one, the new nucleus does not weigh as much as the sum of the original ones. This behavior continues up to the level of the so-called “transition metals”—iron, nickel, and cobalt—in the periodic table. But if two nuclei heavier than iron are coalesced into a single very heavy nucleus found near the end of the periodic table (such as uranium), the new nucleus weighs more than the sum of the two nuclei that formed it.
Thus, if a very heavy nucleus could be divided into parts, energy would be released, and the sum of the weights of the fragments would be less than that of the original nucleus.
In these two types of nuclear reactions, a small amount of matter would actually vanish! Einstein’s Special Theory of Relativity states that the vanished matter would reappear as an enormous quantity of energy.
During the late 1920s scientists began saying that a small amount of matter could supply enough energy to drive a large ship across the ocean. As we know, this prediction has since been borne out by the performance of nuclear submarines and surface vessels.
The NS Savannah was the first cargo-passenger ship to be driven
by nuclear power.
Courtesy States Marine Lines
The Nautilus was the Navy’s first atomic-powered submarine.
Courtesy U. S. Navy
| 1800 | Dalton firmly establishes atomic theory of matter. |
| 1890-1900 | Thomson’s experiments with cathode rays prove the existence of electrons. Atoms are found to contain negative electrons and positive electric charge. Becquerel discovers unstable (radioactive) atoms. |
| 1905 | Einstein postulates the equivalence of mass and energy. |
| 1911 | Rutherford recognizes nucleus. |
| 1919 | Rutherford achieves transmutation of one stable chemical element (nitrogen) into another (oxygen). |
| 1920-1925 | Improved mass spectrographs show that changes in mass per nuclear particle accompanying transmutation account for energy released by nucleus. |
| 1932 | Chadwick identifies neutrons. |
| 1939 | Discovery of uranium fission by German scientists. |
| 1940 | Discovery of neptunium by Edwin M. McMillan and Philip H. Abelson and of plutonium by Glenn T. Seaborg and associates at the University of California. |
| 1942 | Achievement of first self-sustaining nuclear reaction, University of Chicago. |
| 1945 | First successful test of an atomic device, near Alamagordo, New Mexico, followed by the dropping of atomic bombs on Hiroshima and Nagasaki, Japan. |
| 1946 | U. S. Atomic Energy Commission established by Act of Congress. |
| First shipment of radioisotopes from Oak Ridge goes to hospital in St. Louis, Missouri. | |
| 1951 | First significant amount of electricity (100 kilowatts) produced from atomic energy at testing station in Idaho. |
| 1952 | First detonation of a thermonuclear bomb, Eniwetok Atoll, Pacific Ocean. |
| 1953 | President Eisenhower announces U. S. Atoms-for-Peace program and proposes establishment of an international atomic energy agency. |
| 1954 | First nuclear-powered submarine, Nautilus, commissioned. |
| 1955 | First United Nations International Conference on Peaceful Uses of Atomic Energy held in Geneva, Switzerland. |
| 1957 | First commercial use of power from a civilian reactor takes place in California. |
| Shippingport Atomic Power Plant in Pennsylvania reaches full power of 60,000 kilowatts. | |
| International Atomic Energy Agency formally established. | |
| 1959 | First nuclear-powered merchant ship, the Savannah, launched at Camden, New Jersey. |
| Commissioning of first nuclear-powered Polaris missile-launching submarine George Washington. | |
| 1961 | A radioisotope-powered electric power generator placed in orbit, the first use of nuclear power in space. |
| 1962 | Nuclear power plant in the Antarctic becomes operational. |
| 1963 | President Kennedy ratified the Limited Test Ban Treaty for the United States on October 7. |
| 1964 | President Johnson signed law permitting private ownership of certain nuclear materials. |
Enrico Fermi
1901-1954
Courtesy Chemical and Engineering News
Physicists welcomed the neutron as a bullet that could strike any nucleus, unopposed by electric repulsion. During the middle 1930s, a number of investigators, chief among them the Italian physicist Enrico Fermi, exposed many different isotopes of the chemical elements to beams of neutrons to see what would happen.
What usually happened was that the bombarded nuclei would absorb neutrons, emit alpha, beta, or gamma rays, and change into different isotopes. The identification of the extremely small quantities of isotopes produced required the development of a fantastic new branch of chemistry known as radiochemistry, or, as one chemist put it, “phantom chemistry.”
In some cases the absorption of a neutron by a nucleus was followed by the emission of a negative electron (beta particle). This produced an atom whose nuclear positive charge had been increased by one unit and which therefore belonged at the next higher place on the periodic table. Fermi and others then considered the fascinating possibility of doing the same thing to uranium, the last-known element on the periodic table, to create previously unknown chemical elements. The results of bombarding uranium with neutrons turned out to be extremely complex, but it eventually became clear that “transuranic” elements (those heavier than uranium) could actually be made in this way.[2]
Some of the complex results of bombarding uranium with neutrons formed an intriguing puzzle that kept various investigators busy for several years. In 1939 the German chemists Otto Hahn and Fritz Strassmann and the physicists Lise Meitner and Otto Frisch were able to announce a solution. The absorption of a neutron by a certain uranium nucleus (later shown to be that of the relatively rare isotope uranium-235) can result in a splitting, or fission, of the nucleus into two parts with separate weights that place them somewhere near the middle of the periodic table.