Worlds Within Worlds: The Story of Nuclear Energy, Volume 1

It eventually became clear that radioactivity involved the giving off of energy. Uranium emitted gamma rays that we now know to be a hundred thousand times as energetic as ordinary light rays. What’s more, alpha particles were being emitted at velocities of perhaps 30,000 kilometers per second, while the lighter beta particles were being shot off at velocities of up to 250,000 kilometers per second (about 0.8 times the velocity of light). At first, the total energy given off by radioactive substances seemed so small that there was no use worrying 58 about it. The amount of energy liberated by a gram of uranium in 1 second of radioactivity was an insignificant fraction of the energy released by a burning candle. In a few years, however, something became apparent. A lump of uranium might give off very little energy in a second, but it kept on for second after second, day after day, month after month, and year after year with no perceptible decrease. The energy released by the uranium over a very long time grew to be enormous. It eventually turned out that while the rate at which uranium delivered energy did decline, it did so with such unbelievable slowness that it took 4.5 billion years (!) for that rate to decrease to half what it was to begin with. If all the energy delivered by a gram of uranium in the course of its radioactivity over many billions of years was totalled, it was enormously greater than the energy produced by the burning of a candle with a mass equal to that of uranium. Let’s put it another way. We might think of a single uranium atom breaking down and shooting off an alpha particle. We might also think of a single carbon atom combining with 2 oxygen atoms to form carbon dioxide. The uranium atom would give off 2,000,000 times as much energy in breaking down, as the carbon atom would in combining. The energy of radioactivity is millions of times as intense as the energy released by chemical reactions. The reason mankind had remained unaware of radioactivity and very aware of chemical reactions was, first, that the most common radioactive processes are so slow that their great energies were stretched over such enormous blocks of time as to be insignificant on a per second basis. Secondly, chemical reactions are easily controlled by changing quantities, concentrations, temperatures, pressures, states of mixtures, and so on, and this makes them easy to 59 take note of and to study. The rate of radioactive changes, however, could not apparently be altered. The early investigators quickly found that the breakdown of uranium-238, for instance, could not be hastened by heat, pressure, changes in chemical combination, or, indeed, anything else they could think of. It remained incredibly slow. But despite all this, radioactivity had at last been discovered and the intensity of its energies was recognized and pointed out in 1902 by Marie Curie and her husband Pierre Curie (1859-1906). Where, then, did the energy come from? Could it come from the outside? Could the radioactive atoms somehow collect energy from their surroundings, concentrate it several million-fold, and then let it out all at once? To concentrate energy in this fashion would violate something called “the second law of thermodynamics”. This was first proposed in 1850 by the German physicist Rudolf Julius Emmanuel Clausius (1822-1888) and had proved so useful that physicists did not like to abandon it unless they absolutely had to. Another possibility was that radioactive atoms were creating energy out of nothing. This, of course, violated the law of conservation of energy (also called “the first law of thermodynamics”) and physicists preferred not to do that either. The only thing that seemed to remain was to suppose that somewhere within the atom was a source of energy that had never made itself evident to humanity until the discovery of radioactivity. Becquerel was one of the first to suggest this. It might have seemed at first that only radioactive elements had this supply of energy somewhere within the atom, but in 1903 Rutherford suggested that all atoms had a vast energy supply hidden within themselves. The supply in uranium and thorium leaked slightly, so to speak, and that was all that made them different. 60 The room in which the Curies discovered radium. Pierre Curie’s writing is on the blackboard. 61 But if a vast supply of energy existed in atoms, it was possible that the solution to the puzzle of the sun’s energy might rest there. As early as 1899 the American geologist Thomas Chrowder Chamberlin (1843-1928) was already speculating about a possible connection between radioactivity and the sun’s energy. If it were some variety of this newly discovered source of energy (not necessarily ordinary radioactivity, of course) that powered the sun—millions of times as intense as chemical energy—then the sun might be pouring out energy for hundreds of millions of years without perceptible physical change—just as uranium would show scarcely any change even in so mighty a time span. The sun would not have to be contracting; it would not have had to fill the earth’s orbit 25,000,000 years ago. This was all exciting, but in 1900 the structure of the atom had not yet been worked out and this new energy was just a vague supposition. No one had any idea of what it actually might be or where in the atom it might be located. It could only be spoken of as existing “within the atom” and was therefore called “atomic energy”. Through long habit, it is still called that much of the time. And yet “atomic energy” is not a good name. In the first couple of decades of the 20th century, it became apparent that ordinary chemical energy involved electron shifts and those electrons were certainly components of atoms. This meant that a wood fire was a kind of atomic energy. The electrons, however, existed only in the outer regions of the atom. Once Rutherford worked out the theory of the nuclear atom, it became apparent that the energy involved in radioactivity and in solar radiation had to involve components of the atom that were more massive and more energetic than the light electrons. The energy had to come, somehow, from the atomic nucleus. What is involved then in radioactivity and in the sun is “nuclear energy”. That is the proper name for it and in the 62 next section we will consider the subsequent history of the nuclear energy that broke upon the startled consciousness of scientists as the 20th century opened and which, less than half a century later, was to face mankind with untold consequences for good and for evil. FOOTNOTES [1]“Mass” is the correct term, but “weight”, which is a somewhat different thing, is so commonly used instead that in this book I won’t try to make any distinction. 63 QUOTATION CREDIT Inside front cover Copyright © by Abelard-Shuman, Ltd., New York. Reprinted by permission from Inside the Atom, Isaac Asimov, 1966. PHOTO CREDITS Cover The Metropolitan Museum of Art Page facing inside cover The “Horsehead” Nebula in Orion. Hale Observatories. Author’s Photo Jay K. Klein Contents page & page 4 Lick Observatory Page 7 New York Public Library 9 From Discovery of the Elements, Mary E. Weeks, Chemical Education Publishing Company, 1968. 12 Library of Congress 15 Sir George Thomson 18 Burndy Library 19 New York Public Library 21 Copyright © 1965 by Barbara Lovett Cline, reprinted from her volume The Questioners: Physicists and the Quantum Theory by permission of Thomas Y. Crowell Company, Inc., New York. 22 & 23 Curie Foundation, Institute of Radium 26 Academic Press, Inc. 29 Van Nostrand Reinhold Company 31 Top, Nobel Institute; bottom, from Discovery of the Elements, Mary E. Weeks, Chemical Education Publishing Company, 1968. 32 From Discovery of the Elements, Mary E. Weeks, Chemical Education Publishing Company, 1968. 34 Top, Nobel Institute; bottom, Niels Bohr Institute. 36, 42, 44, & 45 Nobel Institute 48 Academic Press, Inc. 49 From Discovery of the Elements, Mary E. Weeks, Chemical Education Publishing Company, 1968. 60 Curie Foundation, Institute of Radium ★ U.S. GOVERNMENT PRINTING OFFICE: 1975—640—285/13 A word about ERDA.... The mission of the U. S. Energy Research & Development Administration (ERDA) is to develop all energy sources, to make the Nation basically self-sufficient in energy, and to protect public health and welfare and the environment. ERDA programs are divided into six major categories: · CONSERVATION OF ENERGY—More efficient use of existing energy sources, development of alternate fuels and engines for automobiles to reduce dependence on petroleum, and elimination of wasteful habits of energy consumption. · FOSSIL ENERGY—Expansion of coal production and the development of technologies for converting coal to synthetic gas and liquid fuels, improvement of oil drilling methods and of techniques for converting shale deposits to usable oil. · SOLAR, GEOTHERMAL, AND ADVANCED ENERGY SYSTEMS—Research on solar energy to heat, cool, and eventually electrify buildings, on conversion of underground heat sources to gas and electricity, and on fusion reactors for the generation of electricity. · ENVIRONMENT AND SAFETY—Investigation of health, safety, and environmental effects of the development of energy technologies, and research on management of wastes from energy production. · NUCLEAR ENERGY—Expanding medical, industrial and research applications and upgrading reactor technologies for the generation of electricity, particularly using the breeder concept. · NATIONAL SECURITY—Production and administration of nuclear materials serving both civilian and military needs. ERDA programs are carried out by contract and cooperation with industry, university communities, and other government agencies. For more information, write to USERDA—Technical Information Center, P. O. Box 62, Oak Ridge, Tennessee 37830. United States Energy Research and Development Administration Office of Public Affairs Washington, D.C. 20545