THE CHEMICAL EXPOSITION it île Iliwi et A t o m i c P o w e r OUR attendance at the Chemical Exposition, Γrvery often we have been aware of a vibrant atmosphere of power and energy, the power of machines and equipment on display and the energy of men who conceive and create new products and processes. Consequently, when we came to consider our part in the exposition our thoughts turned to the most significant development in power and energy ever made by man—the conversion of matter into energy through nuclear reactions. Since the first large-scale demonstration of such power startled the people of the world a few months ago, volumes have been written and spoken on the political and economic implications. Much of what we have read and heard is misinformation and, in many cases, contradictory and fantastic. B u t through all of the discussion rightly runs the thought that we are entering a new era in human events on earth. If some of the statements are fantastic, so actually are the possibilities for good and evil of such a tool in the hands of man, who, on the one hand, has the intelligence to learn such secrets of nature and, on the other, has the stupidity to blast himself and civilization into oblivion. Granted that our intelligence will overcome our stupidity, we have a source of power that never before has been put to work. For example, one ounce of mass is about equivalent to the energy output of the great power plant at Boulder Dam for a whole month. The amount of energy liberated in the fission of uranium or plutonium is pound for pound about three million times as great as in the case of
coal burned in air. An improvement in an ordinary fuel of say 100% would normally be an astounding achievement. How then, can we comprehend an increase by a factor of three million? Of course» i t is perfectly true that only a very small percentage of nuclear energy can now b e harnessed, but even if only a small percentage can be put t o work, w e have energy of a new order of magnitude. In appraising the possibilities of this power w e must realize that there are several and inherent limitations. For example» automobiles with a peasized engine are pure fiction. Even small-size power plants now appear impractical because of the need for large and heavy barriers to protect against dangerous radiations. In spite of such limitations, power plants, under certain conditions, are definitely possible in the near future. In addition to power possibilities a great many fascinating and possibly even more important opportunities are opening up for scientists and technologists in all fields through nuclear research. W e are on the threshold of a whole new field of chemistry with the advent of the synthesis and transmutation of elements, and t h e availability of radioactive isotopes for medical therapy, and chemical and biological research. For these reasons, the exhibit (Booth 7) of the AMERICAN CHEMICAL SOCIETY at the exposition will be devoted t o an educational display of the harnessing and application of nuclear energy. W e cordially invite you to visit us there. T H E EDITORS
Development of Atomic E n e r g y By EDGAR J. M U R P H Y
In OR many centuries the alchemists have dreamed of transmuting one element into another. This remarkable feat has been achieved on what may rightfully be termed a mass-production scale in connection with the development of atomic energy. In order to do this, it was necessary to bring about fundamental changes in the nucleus of the atom—that is, a change in the central core. These changes are accompanied 182
by the liberation of from one million to one hundred million times as much energy as is involved in ordinary chemical reactions such as take place in the combustion of coal or in the usual type of explosion. No doubt one of the questions which are foremost in the mind of the average American is, "What is the source of this tremendous amount of energy?" Einstein partially answered this question for CHEMICAL
us in 1905 when he unquestionably demon· strated mathematically that there is a direct relation between mass and energy, which may be expressed as: Energy = rnase X (velocity of light) 2 This equation simply states that mass and energy are interchangeable. In fact, in the mind of the scientist there is no fundamental difference between mass and energy—or preferably, matter and enA N D ENGINEERING
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ergy—since they are interchangeable a.nd differ only in the manner of their physi cal manifestations. Now, perhaps the next questioQ wkich arises in the average mind is, "Where does the mass come from which gives birth, to this unbelievable quantity of atomic e n ergy ?" The fundamental concepts of the phenomena governing the release of atomic energy can be more easily under stood if one refers to a graphical repre sentation of what the physicist calls fche "packing fraction" of the atomic nuclei. This term is significant in that it e m bodies a measurement of how much t h e actual mass of each isotope differs from a whole mass number. It is also an indica tion of how strongly the particles forming the nucleus are held together. Take, f o r example, the ordinary hydrogen atom which has an actual mass of 1.O0B13 units as measured on the scale which h a s been chosen for comparing the quanti ties of matter contained in the various isotopes. Thus, one sees that tbis i s o tope differs from unity, its mass Quml>er, by an amount of 0.00813 unit. More specifically, the "packing fraction" is defined as: Actual atomic mass — mass nuiribor mass number X 10,000 If a graph is plotted, using t h e mass number as the abscissa and the packLng fraction as the ordinate, there results a curve as shown in Fig. 1. An examination of this curve will show that when the light elements sxich a s hydrogen, deuterium, helium, etc., com bine t o form heavier elements, there w i l l be a loss of mass, since the mass of t l i e new element formed is less t h a n t l i e sum of the masses of the isotopes which were combined. Let us consider t l i e reaction wherein two protons combine with t w o neutrons to form a heliam r m cleus, which m a y be represented in tfctis manner: 2lBl
2He*
-f- 2oN»
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Edgar J. Murphy, now assistant director of one of the atomic energy laboratories at Oak Ridge, Tenn., was born in Luthersville, Ga., November 25, 1901. He received a B.S. degree in science at Iov/a State College in 1927, and the M.S. degree in physics from the same institution in 1928. After teaching physics for two years at Alabama Polytechnic Institute, hè went t o New York University as instructor in physics where he received the P h . D . in applied physics in 1934. From 1935 until 1941 he was an instructor in the physics department at City College of New York. During that time he also carried on fundamental research in nuclear physics and was co-author of several technical papers published in scientific journals. In 1941 he was called to active duty with the Corps of Engineers and in October 1943 he was assigned for duty with the Manhattan District as assistant to the District Engineer, and placed in charge of the pilot-plant operations at Clinton Laboratories, Oak Ridge, Tenn. Later, his duties were broadened t o include the supervision of the general research program sponsored by the Manhattan District a t ten different laboratories. Dr. Murphy, then holding the rank of Major, was discharged from the Army in November 1945.
The masses involved in this reaction are: Mass of 2 neutrons Mass of 2 protons
2.01794 unite 2.01516 unite
This will give a total of The mass of the helium nucleus
4.03310 unite 4.00388 unite
Therefore, the mass difference is
0.02922 unit
This excess mass will be transformed into onergy in accordance with Einstein's equation mentioned above. A simple calculation will show that if 1 gram of helium is produced in this manner, there will be 165 billion calories of energy released. Thus, we see that what appears to be a relatively small amount of mass is equivalent t o a very large quantity of energy. Now, consider an element which lies on the heavy-mass end of the curve, such as U 235 . It has been demonstrated beyond doubt that when a slow neutron collides with the nucleus of a U 2 M atom, it is absorbed and creates an unstable condition, as illustrated in Fig. 2.
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This unstable condition causes the U 286 nucleus to divide or undergo fission— that is to say, it loses its identity as an uranium isotope and breaks up into several fragments. Two of these fragments are elements which lie on the horizontal portion of the curve; but, in addition t o these two transmuted elements, there will be two or more fast neutrons released plus an excess fragment of mass, approximately 1/1000 of the uranium nucleus. This may be illustrated as shown in Fig. 3. Mass into
Energy
The excess mass will be transformed into energy according to Einstein's law and will manifest itself as kinetic energy of the newly formed particles and energy of radiation as shown in Fig. 4. T h e fast-moving particles will lose most of their energy through collision with adjacent atoms, thus causing an increase in temperature of the surrounding medium. When one U 2 3 6 isotope fissions there is liberated a total of approximately 200,000,000 electron volts of energy, this being many million times greater than the energy released in any single ordinary chemical reaction. Hence, the source of atomic energy. The neutrons which are liberated during the fission process are slowed down by collision with other light nuclei and when the proper conditions exist, with regard to lattice spacing, quantities, and purities of material, will collide with other uranium nuclei causing more fissions, which in turn release more neutrons thus causing the reaction t o continue. This is commonly spoken of among scientists as a chain reaction. If t h e rate a t which the chain reaction progresses is controlled, the structure in which it takes place is called a pile, which is nothing more than the proper arrangement of the essential materials, such as uranium and graphite. 183
If the reaction is not controlled, i t will continue at a very rapid ratef resulting in the release of a tremendous amouuit of energy in a very short period of time and, hence, a violent explosion, such as that experienced by the inhabitants of Hiroshima and Nagasaki in August 1945. Few people realize the many formidable problems which had to be overcome before the development of atomic enorgy could become a reality.
Detecting
Deposits
The initial step, and by no means a minor one, had to do with surveying a relatively large fraction of the earth's crust in order to locate sufficiently rich deposits of uranium ore. This task was greatly simplified by the use of an ingenious mechanism known as the GreigerMtiller tube, which proved to be a valuable labor-saving device when combined with the necessary auxiliary equipment. It- has been known for several decades that uranium and its by-products give off rays which produce ionization when they pass through a gas. This phenomenon is the fundamental principle upon which the operation of a Geigei-Muller tube is based. Portable radiation detecting sets were used to great advantage in locating rich deposits of uranium ore. Not only was it possible to detect the presence of uranium ore, but also to distinguish between deposits containing different degrees of richness. This instrument was also used in making surveys to determine the distribution of radioactive materials in the devastated areas where the atomic bombs were dropped. The next major problem was the transportation of the crude ore from the locations of the original deposits t o the processing plants. This was accomplished by a combination of methods requiring the use of airplanes, boats, and railroads. Before the uranium metal could be fabricated into the final form for use in the chain reacting units, it was necessary to remove the many impurities associated with it in the natural state. This obstacle was successfully overcome throuigh the use of a method commonly spoken of as solvent extraction, using ether as the solvent. Through the application! of this method quantities of the order of one ton per day of the brown dioxide were processed, yielding materials of an unbelievably high purity. This highly purified compound was used as a starting point for all uranium metal production.
Uranium
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by the isotope of inass 238, and the subsequent nuclear reactions which take place, a new element is created which is also fissionable by slow neutrons. This new element has a mass of 239 units and an atomic number of 94. It has been given the name plutonium. The chain reacting pile serves as a convenient substitute for nature in producing plutonium on a rela· tively large scale. The nuclear reactions which take place in bringing about this transmutation may be summarized as follows: The uranium atom of mass 238 absorbs a neutron and becomes radioactive, resulting in the emission of an electron from its nucleus. Thus, another nem element is iormed. This new element is called neptunium and is also r&diea^tivi, It, too, ejects an electron from its nucleus and thereby gives birth to the desirei element, plutonium, which is much moi^ stable, even though radioactive. T b
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nuclear reactions which take place in the transmutation of uranium 238 into plutonium may be represented by the following equation: 92UÎ38 + oN l 9 2 U*
39
230 93 Np
>
>
MNp
> 239
02U
239
H
238 Η wPu
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Unfortunately, only a small fraction of the U 238 atoms in the natural metal can be transformed into the new element plutonium. Before this can be used in making a rapid chain reacting unit, or bomb, it must be in a highly purified form. Therefore, it is necessary to iso late the plutonium, not only from the bulk of uranium, but also from the many fission products formed in the transmuta tion process. Since most of these are strongly radioactive, it is necessary to protect the operators from the intense radiations. For this reason, the entire
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Isotopes
It is a well-known fact that uranium, as it exists in the natural state, is composed of two isotopes, one having a mass of 235 units and the other 238. It has been clearly demonstrated througti experimental investigations that only the isotope of mass 235 is fissionable with slow neutrons. However, i t has been shown that through the adsorption of a neutron
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process of extracting plutonium has to be done by remote control methods carried on behind a shield of several feet of concrete. T h e chemical separation process is based o n the fact that plutonium is insoluble in the reduced state and soluble in the oxidized state. Therefore, it is extracted from the conglomeration of isotopes b y a series of oxidation and reduction cycles under rigidly controlled conditions, each one designed to bring about the removal of one or more undesirable impurities. In 1942 the committees charged with the responsibility of shaping the destiny of atomic energy development were confronted with a choice of two methods for procuring fissionable isotopes in a form suitable for practical application—namely, the separation and concentration of the fissionable isotopes of uranium 235, or the production of a new element starting with the isotopes of uranium 238. After careful consideration, it was decided, in order to be more certain of accomplishing the objective, t o expend effort along both lines. The separation of the lighter isotopes of mass 235 from the heavier isotopes of mass 238 may be accomplished by four different methods—thermal diffusion, centrifuge, porous barrier, and electromagnetic separation. Briefly, these methods may be described as follows: Thermal Diffusion Method. Several years ago theoretical considerations, confirmed b y experimental results, clearly indicated t h a t if isotopes of different masses were confined within a region in which a temperature gradient existed, the lighter isotopes would drift toward the hotter
region and the heavier isotopes toward the colder region. Furthermore, if the apparatus is properly arranged, the lighter isotopes will also rise, whereas the heavier ones will tend to drift downward. This method has been successfully developed and effectively used in connection with the development of atomic energy. The enrichment of the material in the isotope of mass 235 is not very great; therefore, the output from this plant was used as feed material for the electromagnetic method described below. Centrifuge Method. The principle upon which the ordinary cream separator operates suggested another method for separating t h e two isotopes of uranium. If a gaseous mixture of the isotopes is placed in a bowl and rotated at a very high speed, the individual isotopes will experience pseudo-gravitational forces which are proportional to their masses. Therefore, t h e heavier isotopes will experience a greater force and consequently be pulled to the outer wall of the rotating bowl whereas the lighter one, being subjected to a lesser force, will be more concentrated in the region near the axis of rotation. The effectiveness of this method for separating isotopes was increased by establishing a strong countercurrent flow of the gases in such a manner that the direction of the flow was downward in the outer part of the rotating container and upward in the axial region. Porous Barrier Method. About 50 years ago, it was proved through experimental investigations that when t w o gases of different atomic masses w*re confined in a region under pressure anù allowed to escape through a porous barrier the lighter
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gas diffuoed through the barrier more readily than the heavier gas. This general principle was applied t o the réparation of the t w o uranium isotopes. The method in general consists of a gaseous mixture (uranium hexafluoride) of the two isotopes confined to one side of a porous barrier and subjected t o a relatively high pressure, while the region on the other side of the barrier is partially evacuated. T h e lighter isotopes will pass through the barrier at a greater rate than the heavier ones, thus providing a method for effecting the separation of the two. The rates at which the t w o isotopes diffuse through the barrier are inversely proportional to the square root of their molecular weights. A simple calculation will show that the enrichment of the gas in the 235 isotope is very small as a result of passing through only one barrier. This obstacle, i m posed by a fundamental law established by nature, was successfully overcome b y operating multiple-stage recycling diffusion units. Electromagnetic Method. When charged particles move through a magnetic field, and at right angles to the direction of the lines of magnetic force, they will be acted upon by a force which will cause them to move in a circular path. The radius of curvature of the path traveled by a particle depends upon its mass. Thus, if we have charged particles of different masses, they will travel along different paths and therefore become separated. In the case of the separation of the isotopes of uranium, a gaseous mixture of the isotopes is provided with suitable means for producing the necessary ionization. An accelerating potential is applied across a slit arrangement which pulls the charged isotopes from the ionizing chamber through the slits and into the magnetic field. T h e heavier isotopes, traveling along a path having a greater radius of curvature than the lighter ones, emerge from the magnetic field a t a point farther out from the center of curvature and therefore separation is effected. According to reports, two billion dollars were spent in the development of atomic energy up to the time of V-J D a y . This fact is only indicative of the magnitude of the undertaking and does not reflect a true picture, in that it fails to give any indication of the many complex and difficult research and engineering problems which had to be overcome. It can be truly said that never in the history of mankind has there been an undertaking which required so much brain power, skill, technique, know-how, and common sense combined with natural resources. The achievement of the ultimate objective was made difficult not only b y having to push the frontiers of science and engineering into unknown regions, but by having to accomplish it in an unprecedented short time. 185
It is a well-known fact that the final objective of the Atomic Energy Project was to produce atomic bombs. The test which took place on J u l y 16, 1945, a t Alamogordo, N . Mex., demonstrated beyond doubt that this objective had been attained. There remains an even greater job which has hardly begun—namely, the practical application of atomic energy t o
the exploration of the fruitful fields which are waiting to be investigated. Few, if any, persons who have been closely associated with the Atomic Energy Project believe that there will be any revolutionary changes in the near future brought about by the development of atomic energy. However, there are very good reasons to believe that through future well-planned and timely investigations, all phases of human life will be profoundly
affected. Predictions are dangerous a n d uncertain; however, it is logical to believe that the advent of nucleonics will have a pronounced effect i n advancing our knowledge and enabling u s to develop a more pleasant environment in which to live. Therefore, i t is safe to predict that, as time goes on, the power of nucleonics will be more fully appreciated aJid the impacts of atomic energy will b>e more widely felt.
The New Term WK7CEéM0WÎ 0memmw*i® Wmwm® fmw° Mtmwmi^ Mm®W€$%$ mmai MS^Ïmt®éÊ, Jgmë$j®€»Ê3Hmtt@r* By ZAY JEFFRIES JTliLECTKONics is now a familiar word. There are electronics trade papers, courses of study, engineers, scientists, books, industries, etc. There are also electronic currents, tubes, circuits, and the like. I t is a generic term coined to embrace a whole field of endeavor relating to electrons, the particles with negative charges forming the outer portions of atoms. T h e definition of electronics may be subject to change from time to time and there m a y be differences of opinion on the definition or scope, b u t the word will remain and it will continue to perform t h e useful functions of a generic name. The release of atomic energy represents the greatest technologic stride in recorded history. A great new field of human e n deavor will unfold a s a result of this magnificent achievement. N e w terms will be forthcoming and new interpretations of older terms will be necessary. This field needs a generic name. "Nucleonics'' is t h e generic name used to some extent within the Atomic Energy Project during the war and its use is now gaining in popularity. The origin is simple and natural. T h e nuclei of atoms are made up of protons and neutrons. All atoms have protons in the nuclei and all, save hydrogen with a mass number "one", have neutrons. The number of protons in the nucleus determines t h e chemical nature of t h e atom now known as the "atomic number" and the number of protons plus neutrons is the so-called "mass number", which is approximately the atomic weight if t h e atomic weight of hydrogen is taken as unity. The term "nucléon" has been in use for several years to mean, either a proton or a neutron. Since released atomic energy and certain other phenomena derived from t h e nuclei of atoms and thus from the nucléons, it seems appropriate that the generic name should be "nucleonics". Adoption of t h e t e r m nucleonics need not change present usages such as n u clear physics, nuclear chemistry, etc.
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These will merely be part of the great field of nucleonics. I n the future we will have nucleonics engineers, scientists, teachers, industries, therapy, laboratories, power plants, and the like. Nucleonics is a generic term embracing the field of endeavor relating t o protons and neutrons. This definition gives ample scope for any desired degree of subdivision in t h e future. While t h e normal homes of nucléons are in t h e nuclei of atoms, the scope of the term nucleonics is not limited to nuclei. " B e a m s " of protons or neutrons, for example, would come within the scope. If "protonics" or "neutronics" are needed in the future, each would be part of nucleonics. Like electronics, the definition and scope of the term nucleonics m a y change from time to time, but t h e word should still perform the useful functions of a generic name. Any important new field consists of a
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few new components added t o mamy of the old. Nucleonics i s no exception. In the Atomic Energy Project there were chemists, physicists, metallurgists, engineers of many varieties, medical men-, biologists, instrument specialists, meteorologists, and, in fact, talent from most of the older' arts and sciences. Since tiie main objective was t h e atomic bonab, the whole would now be regarded as a Eiucleonics project. On the other hand, importajit new fields usually a d d richness to the old. Again, nucleonics is n o exception. I n the future there will be no art or science not affected by nucleonics. Thus, nucleonics will play i t s major roles in which a n y art or science will be used t o attain nucleonics objectives, and its minor roles in which nacleonics is used by other arts and sciences to help achieve other objectives.
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Zay Jeffries, vice president of the General Electric Co., has been w i t h the Manhattan District's atomic energy project from its inception, serving as technical consultant t o the Metallurgical Project Director, A. H. Compton. His timely and well considered counsel based on m a n y years o f experience in t h e field of industiial engineering played a most important part in building the framework on which t h e Metallurgical Project is built. H e contributed many practical suggestions considered from a n industrial viewpoint which proved valuable i n outlining general methods for solving many major problems. He was born at Willow Lake, S. D . , April 22, 1888, and received his B.S. degree in metallurgical engineering from South D a k o t a School of Mines in 1910 and the honorary degree, D.Eng. in 1930. H e also received the D.Sc. degree from Harvard in 1918 and D.Sc. from Case School of Applied Science in 1937. Dr. Jeffries' career has covered a broad field in subject matter as well as organizational connections. In addition t o his official duties, he has devoted time and effort t o the writing of books on metallurgy, engineering, and business. H e has served as consultant to many institutions and has taken an a c t i v e part in several scientific societies. H e was awarded t h e James Douglas Medal o f the American Institute of Mining and Metallurgical Engineers (past president) in 1927 and t h e Sauveur Achievement Award o f the American Society of Metals in 1935. tswKamammm
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