The Nobel Prize in Physics 1939
In 1919 Lord Rutherford discovered that nitrogen can be brought to emit protons by bombardment with alpha particles, according to the nuclearreaction equation:
This discovery meant the initiation of a
new era in natural sciences. However, as long as one was limited
to the use of alpha radiation of naturally radioactive substances
for carrying out nuclear reactions, very strict limits were set
to further development both with regard to the substances which
could produce these reactions, as well as to the quantitative
yield of the reactions.
How then would it be possible, by some method other than the use of radioactive substances, to make available projectiles with sufficient energies to bring about nuclear reactions in an artificial way? Fortunately, the quantum-mechanical treatment of this problem, developed in the meantime, implied that the energy of the particles need not be as high as might be expected from classical theories. Among all the proposals and experiments carried out in different quarters to produce sufficiently fast particles for nuclear experiments, those carried out at the Cavendish Laboratory on Rutherford's initiative were the first to yield a positive result (1932). In this case use was made of a high electrical voltage, up to about 600 kV, to accelerate protons which, upon bombarding lithium, caused a nuclear reaction:
Two years earlier (September, 1930),
however, Lawrence had indicated an entirely new method to obtain
fast particles, i.e. the so-called magnetic resonance
acceleration. This method is based on a brilliant combination of
a constant homogeneous magnetic field and an oscillating
electrical field with constant frequency, whereby the ions move
about in circular orbits with ever-increasing radii, through
stepwise acceleration. The communication on the first simple
experimental model of the "cyclotron" was published in the
same year as the aforementioned experiment with artificially
produced nuclear reactions at the Cavendish Laboratory. Under
Lawrence's guidance and with the assistance of a large number of
skilled collaborators the cyclotron method soon proved suitable
for rapid development towards an exceptionally effective tool for
research in this field. The energies of the particles,
successively obtained by the further development of the cyclotron
method, surpassed significantly that which had been obtained by
other means. The maximum energy of the particles accelerated in
the cyclotron even considerably exceeded the energy values
present in alpha rays of naturally radioactive substances. While
the latter energy is of the order of magnitude of 7 to 8 MeV, the
energy of alpha particles supplied by the cyclotron is, according
to latest reports (November, 1939), up to 38 MeV.
Experiments with heavy hydrogen nuclei as projectiles, with which Lawrence and his collaborators could produce nuclear reactions with practically all elements, proved to be particularly successful.
With regard to the intensities of the radiation produced in the cyclotron, it can be mentioned that a current of over 150 microamperes has been attained, corresponding to the alpha radiation of 30 kg radium. As a comparison it may be mentioned that the entire world stock of purified radium can be estimated at 1 kg.
With the powerful means given to nuclear research by the cyclotron, an explosive development took place in this field. Nowadays, cyclotron installations are built or planned in a large number of laboratories throughout the world. The number of publications on the results obtained with the use of cyclotrons has grown with the speed of an avalanche.
The greatest significance the cyclotron has had is in the production of artificially radioactive substances. True, the discovery of active isotopes was made by the Curie-Joliots in 1933 with the use of alpha particles from naturally radioactive substances, but only with the cyclotron was it possible to produce active isotopes in large quantities. This was, among other things, an essential condition for the use of active elements for biological and medical purposes. On this terrain, where such splendid achievements had already been made, a new field for research and practical applications has been opened, thanks to the cyclotron. To appreciate the strength of the radioactive sources produced for the last-mentioned purposes, the following data may be given. Using deuterium in his cyclotron Lawrence was able, already in 1936, to produce daily quantities of active sodium, which, with regard to gamma radiation, were equivalent to 200 mg radium. The later cyclotrons of larger dimensions (1939) have a production capacity of about 10 times this value.
Finally, it may be mentioned that the cyclotron offers possibilities of producing neutron radiation of great intensity, as a result of which quantitative research on the physical and biological effects of this radiation has been carried out. With regard to therapeutic applications, these preliminary investigations are rather encouraging.
Within the history of the development of experimental physics, the cyclotron takes an exceptional position. It is, without comparison, the most extensive and complicated apparatus construction carried out so far. As to the scientific results achieved, we can scarcely find anything similar among the other experimental tools in physics. It is also evident that the operation and testing of an apparatus of this type, with such a multitude of details, cannot be the merit of one man alone. As promotor and leader of this almost gigantic work, Lawrence has shown such merits in the field of physics that the Royal Swedish Academy of Sciences has considered him as having fulfilled to the highest degree the requirements implied in the award of the Nobel Prize*.
*Owing to the war conditions, the Prize was handed over to Professor Lawrence at a ceremony in Berkeley on February 29, 1940. Among the speeches delivered was a thorough account of Professor Lawrence's work by the physicist R.T. Birge. A report of the ceremonies in Berkeley has been published in "Les Prix Nobel en 1939", Stockholm, 1942.
From Nobel Lectures, Physics 1922-1941, Elsevier Publishing Company, Amsterdam, 1965
* * *
Opening remarks by Dr. R.G. Sproul, Rector, University of California
We are gathered this evening to witness an event which is unique in the history of the University of California. Many of the Nobel Prize winners have lectured and taught for short periods of time on one or another of the University's campuses. Dr. George Hoyt Whipple, now of the University of Rochester, who won a share in the Nobel Prize of 1934 in physiology and medicine, completed much of that fundamental research while he was a member of the staff of the University of California, Director of its Hooper Foundation, and Dean of its Medical School. That same year, the winner of the Nobel Prize in chemistry was Dr. Harold C. Urey, now of Columbia University, who completed his formal training and received his degree as Doctor of Philosophy at the University of California in 1923. But tonight, for the first time, we welcome the opportunity of announcing the award of a Nobel Prize for work which was done in its entirety on a campus of the University of California, and which comes to a man who is a member of its faculty
In citing this fact with some pride I am not being altogether provincial, for, as far as we can determine, this is the first time that any state university in America has had this honor. There is no implication in this that state universities do not have faculties of high calibre. Many of these have found no reason to be embarrassed by national surveys of faculty eminence, such as those of the American Council on Education. As a matter of fact, the University of California at the present time has on its staff twenty-three members of the National Academy of Sciences, out of a total of 308 for all the United States. Moreover, state universities, most of them, labor under a handicap. As soon as a member of their faculties achieves a position within striking distance of a Nobel Prize, one of the more important private universities can usually offer him such a large salary, or such favorable working arrangements, that he leaves the state university. Fortunately that has not happened in this instance and we pray that it may never happen.
Our interest in the event we are celebrating does not arise solely from the fact that the Nobel Prize is the highest scholarly honor that the world has to offer to any man or woman for intellectual achievement. We recognize this fact, naturally, and pay our sincere respects to the young teacher who has made it possible for us to share some of the prestige which this award bestows. But, beyond this local and personal consideration, we recognize a real and special privilege in participating with representatives of our sister nation, Sweden, in the perpetuation of a dream of ideality conceived in the mind of one of her immortal sons, Alfred Nobel.
Despite the sorry spectacle which the world presents today, the bequest of Alfred Nobel remains a sign of progress in the attitude of man to man and of nation to nation. Although nations still visit death and destruction upon one another, they no longer do it with complete clarity of conscience and many men, if, indeed, not all men, even as they enter upon war realize its futility, and know an inner despondency that no strain of martial music, or clank of saber, or roar of guns, or blindly emotional thirst for glory can either overcome or control. This struggling spirit of humanitarianism has hardly more than thrust one delicate tendril above the mud and muck of power politics, but we know that it is planted, and that with reasonable, practical cultivation it will some day come into bearing, and in that day of fruition it will transform this earth.
Alfred Nobel was one of those farseeing men - and there will be others - who have helped to prepare the ground and to plant the seed from which this miracle will eventually come to pass. He lived before his time, of course, for all progress comes through the guidance of men who live before their time. In the austerity of his mind, and the loneliness of his heart, Alfred Nobel found nothing but bitterness in the world of history and the world of his lifetime. But he dreamed constantly of a better world, and he believed in his dreams. There was a period in his life when he thought that his discoveries in the field of high explosives would make war so horrible and so deadly that men would repudiate the force of arms as a means of settling international problems. When that dream proved false he did not give up dreaming. He simply turned to another dream, the dream of promoting the fellowship of mankind; of establishing an award of honor for creative achievements where-ever they might occur, on any continent, and in any country, for men working in the fields of physics, chemistry, physiology and medicine, literature, and peace. With poetic justice that he himself probably appreciated, he dedicated his large fortune, won chiefly from the manufacture of explosives, to these high purposes.
Alfred Nobel did not approve of large bequests to relatives. He looked upon the inheritance of a fortune as a misfortune, a paralyzing influence on the mind and conscience. Nor was he interested, primarily, in bestowing honors, either upon the living or the dead. He wished to lend practical, monetary aid to those who were contributing and might still contribute to civilization and the welfare of mankind. He did not bother with many details concerning the administration of his gift. But, significantly, he put down in specific words: "I declare it to be my express desire that, in the awarding of prizes, no consideration whatever be paid to the nationality of the candidates, that is to say, that the most deserving be awarded the prize." The spirit behind his gift was further indicated by thoughts he had expressed in letters to friends. He once wrote: "My natural inclination is less to honour the dead, who feel nothing, and who must be indifferent to marble monuments, than to help the living."
So each year, since 1901, the nations of the world have submitted the names and records of achievement of their greatest men in five different fields, to the Nobel Foundation at Sturegatan 14, Stockholm, Sweden. And on December 10, the anniversary of Alfred Nobel's death, in Stockholm and in Oslo, the winners of these greatest of international competitions, selected after long and careful deliberation, are presented with their awards at the conclusion of an appropriately dignified and inspiring ceremony. For those who are unable to attend the ceremony and receive the award in Sweden, special ceremonies are held in whatever part of the world may be convenient to the recipient. It is to a contingency of this kind that we owe our privilege tonight. The press of duty, not to mention the present man-made hazards of the oceanic steamship lanes, persuaded Dr. Ernest Orlando Lawrence to forego the pleasure of a visit to Sweden. I hope that we can in some measure compensate for that loss. I hope too, that simple as it is, our ceremony will carry a little of the spirit which prevails in Stockholm on December 10, and that from it each of us may absorb something of the dream that was Nobel's, something that each of us, in his own way, will cherish and nurture.
Were I able, I would like to tell you a little of the accomplishments of Dr. Lawrence on which the Swedish Academy of sciences based its decision to honor him. However, there are others who can do that more accurately if not more cordially than I. On one of these I now call to tell you of the fundamental reason for this meeting - the scientific achievements which Dr. Lawrence and his co-workers have brought about. He is eminently qualified to discharge this responsibility. He has been a member of the University staff for twenty-two years, is chairman of the department in which Dr. Lawrence's research began, and is himself a physicist of national repute, one of the twenty-three members of the National Academy of Sciences of whom I spoke a moment ago. I take pleasure in introducing to you Professor Raymond Thayer Birge.
Mr. President, Mr. Consul-General, Dr.
Lawrence, Ladies and Gentlemen!
South Dakota was admitted to the Union in 1889. It is thus a very young state, and one need not be surprised that as yet relatively few of its native sons have achieved great distinction. One of these few is Ernest Orlando Lawrence, who was born in Canton, South Dakota, on August 8, 1901. Ernest's father, Carl G. Lawrence, is now President Emeritus of Northern Normal and Industrial School, Aberdeen, South Dakota, and is living in Berkeley with his wife. The father of Carl Lawrence was Ole Lawrence, another school teacher, who, as an immigrant from Norway, settled at Madison, Wisconsin, in the year 1840. Ernest's maternal grandfather, Erik Jacobson, also an immigrant from Norway, was a South Dakota pioneer.
Ernest Lawrence is the first native of South Dakota to be elected to membership in the National Academy of Sciences, an honor that came to him in April, 1934, when he was only 32 years old. He is now the first native of South Dakota to become a Nobel Laureate. By an interesting coincidence, one of Dr. Lawrence's intimate boyhood friends, Dr. Merle A. Tuve, is at present in charge of nuclear physics research at the Carnegie Institution of Washington, where a huge 60-inch cyclotron, similar to the large Berkeley cyclotron, is now under construction.
Dr. Lawrence obtained his elementary education in the public schools of Canton and Pierre, South Dakota, and did his undergraduate college work first at St. Olaf College and then at the University of South Dakota, where he was inspired by Dean Lewis E. Akeley to enter the field of physics. He undertook graduate work at the university of Minnesota, the University of Chicago, and finally at Yale University, where he obtained his Ph. D. degree in 1925. At Minnesota ha came under the influence of Dr. W. F. G. Swann, now director of the Bartol Research Foundation, Swarthmore, Pennsylvania, and an authority in the field of Cosmic rays. This influence, which was profound, explains the transfers of Dr. Lawrence from one university to another, for they coincided precisely with similar transfers on the part of Dr. Swann.
After receiving his doctor's degree, Lawrence remained at Yale, first as a National Research Fellow, and then as an assistant professor. When Swann left Yale to become director of the Bartol Foundation, the University of California seized the opportunity to secure the services of a man who already was recognized as one of the most brilliant young physicists in the country. The University of California, after 12 years, still retains his services, in spite of numerous enticing offers that he has received from elsewhere.
The first published scientific paper by Dr. Lawrence is dated May, 1924. In the succeeding 16 years his name has appeared on 56 papers, an average of just three and one-half papers a year. This in itself is a remarkable record, but what is more remarkable is the number of papers by his students and associates - papers that do not bear his name, but that carry only too plainly the impress of his guidance and inspiration. His first paper, entitled "The Charging Effect Produced by the Rotation of a Prolate Iron Spheroid in a Uniform Magnetic Field", contains no trace of his future interests. One of these interests, however, appears in his doctor's thesis, which lay in the field of photoelectricity. Further work in this field was carried out both at Yale and at California. In fact, Dr. Lawrence's first Ph. D. student, N. E. Edlefsen, did his thesis in this field. We shall hear of Dr. Edlefsen again.
From the start of his scientific career, Dr. Lawrence showed an exceptional breadth of interest. While a National Research Fellow at Yale, he measured the ionization potential of the mercury atom. This was, at the time, the most precise determination of its nature that had ever been made. Its importance is due to the fact that the result enables one to calculate the value of the so-called Planck constant, h, one of the four most important universal constants of nature, and the fundamental constant of the quantum theory. There is, however, another point of interest in this research. The ionization potential of the mercury atom is merely the energy required to tear an electron loose from a neutral mercury atom. Now the word "atom", as all of you know, means something that cannot be divided, although, as all of you also know, carving up atoms into little bits is at present the favorite pastime of physicists. Hence when Lawrence thus pried loose an electron from a mercury atom and measured precisely the energy required to do this, he in one sense disintegrated the atom. But it takes only a relatively trifling amount of energy - some ten volts in the case of mercury - to remove one of these so-called external electrons from an atom, and now-a-days we reserve the name disintegration for a process by which the nucleus of the atom is in some way changed, the resulting atom having, in general, completely different chemical properties and being, in fact, a different element. Such a disintegration requires energy equal to millions, rather than tens of volts to bring about, and it is the discovery of a practical method for obtaining by artificial means such high energies that has brought Dr. Lawrence his present fame.
Before, however, Lawrence had settled down to atom smashing in a serious way, he did other interesting things. One of these was the development, in cooperation with Dr. J. W. Beams, of a successful method for obtaining time intervals as small as three billionths of a second. After he came to California, Lawrence and his students applied this method, which involves the use of a Kerr Cell, to a study of the phenomena occurring in the early stages of the discharge of an electric spark. Since a single spark lasts for only about one-millionth of a second, it is obvious that an extremely short "exposure" must be used to photograph the details of its development.
Another of Dr. Lawrence's inventions - if you wish to apply that term - was a new and very precise method for measuring e/m, the ratio of the charge to the mass of an electron. This ratio is another of the fundamental constants of nature. The detailed development of the method was carried out by one of his students, Dr. F. G. Dunnington, whose final result is possibly our present most accurate value of this important constant. So much for the work of Dr. Lawrence outside the field of atomic disintegration. The picture has been sketchy; yet I hope it has indicated the versatility of his ideas.
Then one evening almost exactly ten years ago today, Dr Lawrence happened to glance at an article which had just appeared, by a German physicist, R. Wideroe. He did not actually read the article, but his attention was drawn to a diagram of the apparatus. With this apparatus, Wideroe, by the use of a 25,000 volt potential drop, had succeeded in imparting to atoms of potassium, energy equal to that resulting from a 50,000 volt drop. As a matter of fact, the particular idea used by Wideroe was not new - it had been suggested ten years earlier - but Wideroe was the first one to apply it successfully. Now Lawrence had for some time realized the growing importance of the field of nuclear physics, and had been looking for ways and means of successful experimentation in the field. This paper by Wideroe immediately suggested to him the general idea of producing the very high energy particles required for atomic disintegration, by means of a succession of properly timed "pushes", each of which might be relatively small. Then and there he began sketching various ways of carrying out this idea. Wideroe had used two hollow cylinders, lined up on the same axis. Lawrence sketched a series of such cylinders, but in the case of atoms of small mass, which are most effective in nuclear disintegration, the necessary length of the apparatus would then be too great. He next thought of the possibility of using a curved path. Now an electrically charged particle, entering into a magnetic field directed at right angles to the motion of the particle, proceeds to move in a circle constant speed. Moreover, the time to move through a half circle depends only on the charge and mass of the particle and on the strength of the magnetic field. It does not depend on the speed of the particle. The greater the speed, the greater the radius of the circle in which the particle moves. This important fact, which Dr. Lawrence immediately noted by writing down a very simple mathematical relation, gave him the idea of the present essential features of the cyclotron. All this happened within a few minutes of the time he had seen Wideroe's paper. The next morning Dr. Lawrence told his friends that he had found a method for obtaining particles of very high energy, without the use of any high voltage. The idea was surprisingly simple and in principle quite correct - everyone admitted that. Yet everyone said, in effect, "Don't forget that having an idea and making it work are two very different things."
It seems to me that, in this connection, I can quote with profit some remarks made by Dr. W. D. Coolidge, director of the Research Laboratory of the General Electric Company, when he presented to Dr. Lawrence, in 1937, the Comstock Prize of the National Academy of Sciences. This prize, awarded only once in five years, is considered the greatest honor at the bestowal of the Academy. Dr. Coolidge first sketched the classical experiment of Lord Rutherford, in 1919, when, by using the alpha particles ejected by a radioactive substance, he succeeded in changing nitrogen into a form of oxygen. This was the first true disintegration of matter produced by man, and as such, an experiment of epoch-making importance. As Dr. Coolidge notes, Rutherford succeeded in thus breaking up nitrogen and other light atoms, but to disintegrate heavy atoms, particles of still greater energy appeared to be needed. Such high energy particles, to use as bombarding projectiles, could obviously be produced artificially, by allowing charged particles to fall through sufficiently high voltages. There would be, however, great difficulties in developing tubes to withstand such voltages. Dr. Coolidge then goes on to say:
"Dr. Lawrence envisioned a radically different course - one which did not have those difficulties attendant upon the use of potential differences of millions of volts. At the start, however, it presented other difficulties and many uncertainties, and it is interesting to speculate on whether an older man, having had the same vision, would have ever attained its actual embodiment and successful conclusion. It called for boldness and faith and persistence to a degree rarely matched."
That is the end of the quotation. Those who have worked with Dr. Lawrence during these past ten eventful years can well testify that it did indeed call for "boldness and faith and persistence to a degree rarely matched.' The story of the development of the cyclotron reads like a fairy tale. To be told properly, many hours would be required.
But we are living in a practical world, and it is the results actually achieved by the use of the cyclotron, rather than the details of its development, that have caught the attention of everyone, scientists and non-scientists alike. This fact was recognized by the Swedish Academy of Sciences, when it awarded the prize to Dr. Lawrence with the citation - "for the invention and development of the cyclotron and especially for the results attained by means of this device in the production of artificial radioactive elements".
It is important to note at this juncture that the cyclotron was not the only method devised by Professor Lawrence for the production of high energy particles without the use of high voltages. Another method, already mentioned, employs a series of cylinders set on a common axis. Such a device, called by Lawrence a "linear resonance accelerator" was actually constructed and used by him and several of his students for accelerating heavy particles to high energies. I have already noted that an apparatus of this type is not suitable for light particles, because of the required size. Still a third piece of apparatus, the double linear accelerator - a modification of David Sloan's remarkable x-ray tube - was tested at considerable length. The cyclotron, however, finally proved superior to any other device, and it is only because of this fact that eventually these other methods were dropped, and all attention concentrated on the cyclotron. Even as late as 1934 Lawrence believed that the double linear accelerator would surpass the cyclotron in its yield of neutrons, but such proved not to be the case. The cyclotron is thus not a lucky accident, but a piece of apparatus that has, after detailed development, finally proved its superiority to several other methods of attack devised by Dr. Lawrence.
The first cyclotron, only four inches in diameter, was constructed of glass and red sealing wax, in January, 1930, by Lawrence and Edlefsen, who, as previously noted, was Lawrence's first Ph. D. student at California. Actual resonance effects were obtained, and the first public announcement of the new method was made by Lawrence and Edlefsen at the meeting of the National Academy of Sciences at Berkeley, in September, 1930. A metal cyclotron of the same size was then constructed by Lawrence and M. S. Livingston, who was prominently identified with the development of the cyclotron during the next few years. With this almost toy-like instrument, as viewed in retrospect, a beam of hydrogen molecular ions was generated whose energy corresponded to that produced by 80,000 volts, although the highest potential difference in the instrument was only 2,000 volts.
Spurred by his success, Lawrence next built an eleven-inch cyclotron. This instrument cost $ 1,000, plus some borrowed equipment. With it one and one-quarter million volt hydrogen ions were obtained, the most energetic beam of particles ever produced in the laboratory up to that time. This beam of ions was used, during the summer of 1932, to disintegrate lithium, the first artificial disintegration of matter to be carried out in the western hemisphere. That year, 1932, was by all odds the most exciting in the history of modern physics. Heavy hydrogen was discovered by H. C. Urey at Columbia University, the neutron was discovered by James Chadwick at the Cavendish Laboratory in England, and the positive electron, or positron, as it is usually called§, was discovered by C. D. Anderson at the California Institute of Technology. Each of these discoveries was later honored by a Nobel Award.
The University of California is especially interested in heavy hydrogen, for not only did Urey get his doctor's degree at Berkeley, but the existence of heavy hydrogen was predicted here, and after its discovery, G. N. Lewis was the first person to obtain it in high concentration. Samples of highly concentrated heavy hydrogen were then generously supplied for research work in all parts of the world. But nowhere did this new material prove more useful than right here in Berkeley. Employed as a bombarding projectile in the cyclotron, heavy hydrogen, or deuterium as it is now called, was found to be extraordinarily effective in producing nuclear disintegrations. Furthermore, the cyclotron is by far the most efficient device for generating neutrons in relatively large quantities, and neutrons, in turn, cause many new types of nuclear disintegration. Thus the development of the cyclotron has not only paralleled important discoveries elsewhere, but the cyclotron itself has made possible perhaps the most important applications of these discoveries.
The last great discovery that has since played an important role in the usefulness of the cyclotron is that of artificially induced radioactivity. This discovery was made by F. Joliot and his wife, Irene Curie-Joliot, at Paris, in January, 1934. Again a Nobel Award promptly resulted.
But let us return to the development of the cyclotron. Although million volt hydrogen ions had proved sufficient to disintegrate the light lithium atom, it was well known, as stated in the quotation from the presentation address by Dr. Coolidge, that much higher energies would be needed in order to disintegrate heavier elements. To produce particles of these higher energies, a cyclotron far larger than an eleven-inch instrument was obviously necessary. The figure, eleven inches, refers to the diameter of the vacuum chamber in which the ions revolve in circles of ever-increasing radius, until finally they are removed through a special port-hole in the wall of the chamber. Since this spiralling movement is produced by a uniform magnetic field, it is necessary that the pole faces of the magnet be at least as large as the diameter of the vacuum chamber. Now even the eleven-inch cyclotron employed one of the largest magnets then to be found in a scientific laboratory. Hence the construction of the much larger instrument now needed meant moving from the realm of physics into that of engineering; and that is just where most physicists would have stopped. Not so with Dr. Lawrence. He moved literally into the field of engineering, by appealing to our own Professor L. F. Fuller, at that time also Vice-President of the Federal Telegraph Company. Dr. Fuller had just what Lawrence needed, a gigantic magnet built for a radio transmitter ordered by the Chinese government, but obsolete in type before delivery was possible. Thus a "white elephant" to Dr. Fuller became a godsend to Dr. Lawrence. With this magnet as the basis, the first really large cyclotron was built during that eventful year, 1932. The diameter of the pole faces is 37 inches, but the actually used portion of the original vacuum chamber was only 13 inches in diameter. Numerous engineering as well as scientific problems had to be solved, before it was possible to employ completely a 37-inch chamber, as is being done at present. In fact only those directly associated with the work of the Radiation Laboratory can appreciate fully the innumerable difficulties that have arisen and have, one by one, been conquered. As I have already indicated, the present cyclotron is primarily the result not of a moment's inspiration but rather of years of perspiring effort. The 37-inch cyclotron is now installed in the old Radiation Laboratory. It weighs some 75 tons.
The present world's largest cyclotron is the 220-ton instrument, located in the new William H. Crocker Radiation Laboratory. The vacuum chamber is 60 inches in diameter, and it produces 100 microampere currents of 16 million volt deuterons. The beam, emerging into the air, has a diameter of a few inches, and penetrates some five feet. It is our nearest approach to a "death-ray". Just what is the constitution of such a beam? The heavy hydrogen nuclei composing it are moving, when they emerge from the cyclotron, with a speed of some 25,000 miles a second - about 13 per cent of the velocity of light. The number of individual atoms, issuing from the cyclotron per second, is 600 million million! To obtain an equally dense beam of particles from radium would require something like thirty tons of pure radium, and even then the energy of the individual particles would not be nearly so great.
By causing the cyclotron beam to fall on a piece of beryllium, disintegration of the beryllium atoms is produced, accompanied by a copious emission of neutrons. These particles, equal in mass to the hydrogen atom, but with no electric charge, were produced originally by allowing the radiation from some natural radioactive substance, such as radium emanation, to fall on beryllium. To equal, in this way, the neutron yield of the cyclotron, some 200 pounds of radium would be required - and radium costs nearly a million dollars an ounce! Thus the number of high energy particles produced by the cyclotron is of a completely different order of magnitude from that given by any other source. Herein lies the great practical value of the instrument.
When one turns more specifically to the uses of the cyclotron, the wealth of material is so great that it is difficult to know what to select for presentation, in the few remaining minutes at my disposal. It is doubtful if any scientific instrument invented by man has found more varied and more important applications. Lawrence originally designed the cyclotron in order to disintegrate atomic nuclei, and thus to gain information in regard to the structure of the atom. At the present time every element, without exception, has thus been disintegrated, a new element being in general produced. If one wants gold, Lawrence will take mercury and turn it into gold. But the process is far more costly than the value of the gold produced. In fact, the one great possibility of the cyclotron, as a money-making instrument, lies not in making gold, or platinum, or any other so-called precious substance, but in releasing nuclear energy. We now know that nearly all of the energy of the universe is locked inside the nuclei of atoms, and we have found recently that even slowly moving neutrons have the ability to cause the nucleus of uranium to explode into two more or less equal parts. In this process some 200 million electron volts of energy are released. To visualize this amount of energy, consider the fact that when an atom of carbon is burned to form carbon dioxide about four electron volts of energy are released. As yet this uranium disintegration has not been developed into a self-sustaining process, such as is needed for the commercial production of energy. But with the far more energetic particles that Dr. Lawrence hopes to produce with a much larger cyclotron, other more suitable types of disintegration may well be found. The practical aspects of such an unlocking of nuclear energy, if it is accomplished, are so staggering that some of us shrink even from contemplating them.
With the cyclotron one can, as stated, transform every stable element into other forms. Some of the final products are themselves stable, but most of them are radioactive. The cyclotron is by far the best device for producing new radioactive substances. There are about 90 different elements, but most of these can exist in several different stable forms, known as isotopes. There are now some 386 known stable forms. In addition there are about 335 artificially produced radioactive substances, of which 223 have been discovered by means of the cyclotron. More than half of the 223 have been found here in Berkeley. The remainder have been discovered by means of some one of the 21 cyclotrons now in operation at other institutions. An additional 17 cyclotrons are under construction. Directing or assisting in work of this kind at 25 different institutions are 47 men, trained for longer or shorter periods of time in the Berkeley laboratory.
Many of the artificially produced radioactive substances are proving of extraordinary value in medicine and in biology. Others are of great interest in themselves. I give just one illustration of the latter class. A few years ago it was believed that every element in the periodic table had been found, with the exception of the elements of atomic number 85 and 87, the hypothetical elements known as eka-iodine and eka-caesium, respectively. Then it became apparent that there was no valid evidence for the claimed existence of stable element 43, called masurium by its apparently deluded discoverer, nor for element 61, called illinium. Quite recently, Dr. Emilio Segrè, a member of the staff of the Radiation Laboratory, has definitely found a radioactive form of element 43, among the products produced by the cyclotron, and he has published several papers on this subject. I now have the privilege and the honor to make the first public announcement of another similar discovery. Dr. Dale Corson, a member of the Physics Department staff and of the Radiation Laboratory, aided by Dr. Segrè, Dr. J. G. Hamilton and Mr. K. R. Mackenzie, has found what appears to be clear evidence of a radioactive form of element 85, eka-iodine. All possible alternatives are not yet excluded, but the evidence is much stronger than that on which the announced discovery of several new elements has been based. Meanwhile the discovery of eka-caesium, element 87, has recently been announced from Irene Curie-Joliot's laboratory in Paris. That leaves only element 61 still missing, and there is a strong probability that a radioactive form of this element will be found among the disintegration products yielded by the cyclotron beam.
The great importance of radioactive elements in medicine and in biology results chiefly from their use as so-called "tracer atoms". One can, for instance, make a radioactive form of sodium that does not differ chemically from stable sodium. Taken through the mouth in the form of common salt, these radioactive atoms travel with surprising rapidity to various parts of the body. Any one such atom may exist for many hours, or only for a fraction of a second, but the average life of an atom of radio-sodium is about 21 hours. When it does die - by transformation into a new element - each atom gives unmistakable evidence of its location by ejecting a high-speed particle, which may be recorded with a so-called Geiger counter. Thus the wanderings of single atoms may be accurately followed in chemical and biological processes. The eminent physiologist, Professor A. V. Hill, has told Professor Lawrence that, in his opinion, the use of such tracer elements will be recorded in history as a technique of equal importance with the use of the microscope. Just because of these facts, chemists, biologists, cytologists, bacteriologists, physicians, and radiologists - to make only an incomplete list - are now working with these products of the cyclotron, in close cooperation with the regular staff of the Radiation Laboratory. Samples of radioactive material are being supplied to at least twenty such groups, some located on the Berkeley campus, and others at institutions all over the world.
Radioactive elements are used not only as tracer atoms. They are now being used also in the direct treatment of various diseases, and the results in certain cases, such as chronic leukaemia, are distinctly encouraging. Finally, the neutron rays produced by the cyclotron are found to have many applications in both biology and medicine, quite aside from their importance to physicists. They have already shown very promising possibilities in the treatment of cancer, and other medical uses are constantly being found. In the medical work of the Radiation Laboratory, Dr. Ernest Lawrence is fortunate in having the cooperation of his brother, Dr. John Lawrence, a medical scientist of great ability. Although I have neither the time nor the competence to discuss in detail these manifold uses of the cyclotron and its products, I hope that I have given at least a glimpse of their extent. Already 163 papers have been published from the Berkeley Radiation Laboratory itself, and 76 different names appear on these papers.
The progress of science is the progress of instruments. A scientific theory is meaningless unless it can be tested experimentally. Such a test normally requires an appropriate instrument, and thus, for the testing of theories as well as for the direct observation of facts, instruments are indispensable. One needs only think of what would remain of astronomy without the telescope or of biology without the microscope. The cyclotron is now playing a similar role in the infant field of nuclear physics. But the cyclotron, as noted, has a unique additional value, due to the fact that it manufactures, in relatively large amounts, various products, each of which is itself already of tremendous importance in widely varying fields. It is therefore a real tribute to refer to Dr. Lawrence as an eminent inventor. This idea has already been expressed in a beautifully worded editorial in the New York Times, a portion of which reads as follows:
"The pioneers in experimental physics have always had to devise their own instruments of investigation. Men like Faraday, Hertz and Helm-Holtz are not listed among the great inventors. For the servants of science invent as a matter of course, rarely take out patents, and concentrate on research. Who thinks of Hertz's simple detector of electric waves as the first wireless apparatus, or of the apparatus with which Faraday discovered electromagnetic induction as the germ of the electric generator and motor? If Professor Lawrence were what is called a 'practical' inventor and his cyclotron were of any immediate commercial use, he would take his place beside Watt, Arkwright, Bell, Edison and Marconi, which would probably exasperate rather than flatter him."
That is the end of the quotation.
I cannot close without commending the completely unselfish attitude of Dr. Lawrence toward his associates. This is well shown by his first remark on being informed of the Nobel Prize Award - namely, "It goes without saying that it is the laboratory that is honored, and I share the honor with my co-workers past and present."
The development of the cyclotron has taken the united efforts of many most capable and willing workers, but it is the ability and the inspiration of Lawrence that have brought these workers together, and have held them together, in spite of every obstacle, until today the Radiation Laboratory represents as fine a piece of cooperative effort as exists in the annals of science. I therefore pay tribute to Dr. Lawrence not only as a scientist of real distinction, but as one who exemplifies the best in scientific ideals.
Remarks by Mr. C. E. Wallerstedt, Consul General in San Francisco
Mr. President, Professor Lawrence, Ladies
Alfred Nobel, Swedish scientist and inventor, who died in the year of 1896, left practically his entire fortune to further the welfare of humanity.
By testamentary disposition Alfred Nobel chose five fields of human endeavor, in which he desired each year to give distinction and an award to those outstanding men or women, who above all others by their work during the preceding year had conferred the greatest benefit on mankind.
Three of these fields are purely scientific, namely Physics, Chemistry, and Physiology and Medicine. Science has always been international. So have been the thoughts focused on the big problems of international rights, disarmament, and ultimately the elimination of war. This fourth field Nobel also wished to encourage.
Literature was selected as the fifth field for recognition, that is, literature of an idealistic tendency. Although literature might be thought to be but purely national, in a very real sense all great literature is international and transcends the bounds of any one country. The soul of a people is expressed in its literature, and, as a result, such works become a means of creating international understanding and sympathy.
Whether the field be science, international conciliation, or literature, the aim and purpose are the same, that is, the realization of the ultimate hope that we human beings, regardless of race or creed, while recognizing the difference between us, shall live and let others live in harmony and peace.
The first Nobel prizes were awarded in 1901. In the intervening years, many of the prizes, in all five fields, have been awarded to Americans. Ordinarily the prizes are delivered to the recipients at Stockholm on the festival day of the Nobel Foundation, the l0th of December, which date was chosen because it is the anniversary of the testator's death.
The Royal Swedish Academy of Science, which has the honor and responsibility of making the awards, has announced that the Physics prize for 1939 has been bestowed upon an eminent member of the faculty of the University of California, Dr. Ernest Orlando Lawrence, director of the Radiation Laboratory of the University and Professor of Physics. The award is made in recognition of his invention of the Cyclotron, of its development, and of the results gained therefrom, especially with reference to the production of artificially radioactive elements.
Because of international complications the young and famous scientist was not able to be present in Sweden on the festival day and personally receive from the hand of His Majesty the King the Medal and Diploma, which constitute part of the Nobel Award.
It therefore becomes my delightful privilege as the representative of Sweden to serve on this occasion and, in behalf of the Royal Swedish Academy of Science, to present to Dr. Lawrence this Medal and Diploma and at the same time to express the hope, that before long conditions will permit him to visit Sweden and to deliver publicly the anticipated Nobel lecture concerning his researches in the field, in which he has achieved such great distinction.
This occasion provides the opportunity not only to give recognition to the work of a great scientist of the University of California, but also to express the friendship and good will, which Sweden has always felt and feels toward the United States of America.
From Les Prix Nobel en 1939, Editor Arne Holmberg, [Nobel Foundation], Stockholm, 1940
Copyright © The Nobel Foundation 1939