Glenn Seaborg and Edwin MacMillan
1951 Nobel Prize for Chemistry
| Presentation of Award
Biography Submitted by Dr. Seaborg to the Nobel Committee
Biography Submitted by Dr. McMillan to the Nobel Committee
Presentation of Award: 1951 Nobel Prize for Chemistry
Your Majesties! Your Royal Highnesses! Ladies and Gentlemen!
In his famous treatise on air and fire, published in 1777, Scheele writes that in some quarters at that time it was regarded as futile to make any more research into what elements bodies might consist of. "A depressing prospect," he adds, "for those whose greatest pleasure it is to study the composition of substances found in nature." Scheele's own experience and the subsequent developments up to our day have shown that, at the end of the 18th Century, there certainly still was enough to do for those who wanted to discover new elements. At least as many elements as were then known still remained to be discovered.
These two discoveries together provided the starting-point for studies of the so-called rare earth elements which went on throughout the 19th Century. Already Gadolin had reckoned with the possibility that the yttria isolated by him was not a simple substance and it proved indeed later to consist of several oxides. Berzelius' ceria turned also out to be a mixture. The separation of the different components in these compound earths has been no easy task, since they are chemically very similar to one another. Little by little, however, it has been possible to divide them up completely, and within this group alone as many as 14 different elements have been isolated. Swedish chemists, chief among them being Mosander and Cleve, have made very valuable contributions in this domain of chemistry. Of the rare earth metals many--yttrium, terbium, erbium, ytterbium, scandium, thulium, holmium--have been given names that show their origin in various Swedish localities.
Besides this group of closely connected rare earth metals many other elements were discovered in the course of the 19th Century. A comprehensive survey of all the known elements was provided in 1869 by the establishment of the periodic system. At that time Mendelejeff and Lothar Meyer independently discovered that there were clear evidences of periodicity in the chemical character of the elements when they were arranged in the order of increasing atomic weights. From this regularity Mendelejeff was able to conclude that certain gaps remained still to be filled, and he could even predict all the most important properties of these still undiscovered elements and their compounds. His predictions have been fully confirmed by later discoveries.
During the years around 1920, Nils Bohr's investigations on the structure of atoms threw new light on the periodic system. It was now possible, among other things, to explain the chemical similarity between the rare earth elements. The positive charge in the nucleus of the atom and the number of electrons surrounding it rises by one unit for every step upwards in the element series. This additional electron usually forms part of the outermost shell of the atom, and since the chemical characteristics depend on the structure of the atom in just this part, the successive members in the series of elements can for the most part be clearly distinguished from one another in respect to their chemical properties. But within the group of the rare earths it is not the outermost electronic shell that is developed, nor the shell beneath it, but the one that underlies that.
If, said Bohr, there existed an extension of the series of elements beyond the heaviest of them all, Nr92, uranium, then this would form a new series of very closely associated elements. They would all resemble uranium and by analogy with the lanthanides, would form a series of uranides.
By experiments which were carried out during the years 1936-38, Otto Hahn and Lise Meitner believed they could confirm Fermi's statement that the transuranium elements are formed by irradiating the heaviest elements with neutrons. But these synthetic elements were not like uranium, but appeared to be homologues of elements so dissimilar to one another as rhenium, the platinum metals, and gold. Hahn and Strassman made, however, late in 1938 the epoch-making discovery that is was not really a question of transuranium elements here at all. The heavy atoms were found to split up into substances belonging to the middle of the elemental series and this brought the whole problem into a new stage.
In 1940 McMillan and Seaborg and their fellow-workers had already reported that when neptunium disintegrates it gives rise to an element 94. By analogy with the way in which names had been found for neptunium and uranium, this second transuranium element was called plutonium, after the planet Pluto, which has its orbit next outside that of Neptune. The first isotope of this element, which has a half-period of 24,000 years and thus is relatively stable, is what is called an atomic fuel. This plutonium isotope reacts with slow neutrons in the same way as the uranium isotope
U235, that is to say--when it is split it develops great energy and gives off neutrons. In this way it came to play an important part in the atomic bomb project during the war, and methods were developed for its production on a large scale.
After these problems, conditioned by the war, had been solved, Seaborg, as leader of a comprehensive group of able colleagues, completed the studies of the transuranium elements. In doing this, he has written one of the most brilliant pages in the history of the discovery of chemical elements.
Not less than four more transuranium elements have been produced. The chemical characteristics of these new elements have been established by developing a refined ultra-microchemical experimental technique. Bohr's prophesy that in the transuranium elements we are dealing with a group of substances of the same sort as the rare earth metals, has thus been confirmed. However, this new series of closely associated elements does not begin with 92 uranium, but with 89 actinium. Thus, corresponding to the lanthanides, there are the actinides, and a certain agreement can be found between every member in these two series. Seaborg therefore proposed for the new trans-uranium elements 95 and 96 the names americium and curium, in analogy with their corresponding rare earths europium and gadolinium (after Europe and Gadolin respectively). The two transuranium elements most recently discovered, berkelium and californium, correspond to terbium and dysprosium in the lanthanides.
By irradiating different sorts of heavy atoms with neutrons, protons, deuterons, helium nuclei, or, most recently, carbon nuclei, a great number of isotopes have been produced from the six transuranium elements. The study of these isotopes' formation and properties has yielded a wealth of scientific material.
1A great many, originally isolated, observations on the radioactive transmutation series were made during the work on the great plutonium project. Thanks above all to Seaborg's activities it has been possible to bring these observations together into a comprehensive wholeness. In this way there was discovered an entirely new radioactive series which, from its most long-lived member is now called the neptunium family.
The mass numbers of the three radioactive families which were previously known have the form 4n (thorium series) 4n + 2 (uranium series) and 4n + 3 (actinium series). Here the neptunium series fills a gap with mass numbers of the form 4n + 1.
The Swedish Academy of Sciences is of the opinion that these discoveries in the realm of the chemistry of the transuranium elements, of which I have here tried to give a brief account, are of such importance that McMillan and Seaborg have together earned the 1951 Nobel Prize for Chemistry.
© the Nobel Foundation 1952
I would like to say how much I appreciate this honor and how deeply impressed I am by this ceremony and by what it represents. There has never been in the history of the world any other prize or honor with the international recognition accorded to the Nobel Prize. One reason for this is that it is truly an international honor, given with regard to achievement only. It is very greatly to the credit of the Swedish and Norwegian nations, and to the organizations and individuals in those nations who have administered the giving of the Prizes, that this high ideal of Alfred Nobel has been maintained. The world would be a more agreeable place if similar ideals governed more of its affairs."
© the Nobel Foundation 1952
This is a translation of Dr. Seaborg's speech, which was given in Swedish. This speech was given by Dr. Seaborg at the Nobel dinner following the presentation of the awards, on December 10, 1951. The dinner was held in the Gold Hall, described by Dr. Seaborg as "...a beautiful room done in gold, as the name implies; around the room are scenes depicting the whole of Sweden's history." The dinner was attended by the Nobel Laureates and their spouses, the Swedish Royal Family, the Prime Minister and other dignitaries. After dinner, Dr. Seaborg made a toast, the translation of which follows:
Your Majesty, Ladies and Gentlemen:
I shall try to say a few words in Swedish. The Nobel Prize has a high value among scientists over the whole world. Indeed, it is the highest honor that a researcher can obtain. Why is this the case? It is not only because of the money. One can look at the list of the scientific researchers that have won the Nobel Prize over the years, then one sees how well the Swedish Royal Academy of Science has done its job. The Swedish Royal Family has also helped give value to the Prize beccause the King himself bestows the Prize.
I am very thankful that I and my co-workers have been able to conduct researches that the Swedish Royal Academy of Science believes deserve the bestowal of the Nobel Prize. I can only hope that the new elements that we have found will be used for the good of mankind. And finally, I would like to thank the Academy for honoring me and my co-workers in the manner that they have.
© the Nobel Foundation 1952
Biography Sumitted by Dr. Seaborg to the Nobel Committee
GLENN THEODORE SEABORG.
He entered the University of California at Los Angeles in September, 1929, earning his way through school by working at various jobs. By 1931 he had been accepted as an assistant in the University's chemistry laboratory preparing samples and doing some research and teaching. During his last two years, through his courses at the university, nuclear physics and chemistry captured his imagination and he concluded that he would pursue this field. In 1934 Seaborg received his A.B. degree and transferred to the University of California at Berkeley. There in 1937 he earned his Ph.D., his thesis subject being the inelastic scattering of fast neutrons. The following two years he was laboratory assistant to Dr. Gilbert Newton Lewis, then Dean of the College of Chemistry on the Berkeley campus.
In 1939 he received his appointment from the University of California as an Instructor, and in 1941 he was promoted to the rank of Assistant Professor. From 1942 to 1946, he was on leave of absence from the University of California acting as chief of the section working on transuranium elements at the Manhattan Project's wartime Metallurgical Laboratory at the University of Chicago. Shortly after he joined the Manhattan Project in 1942 he married Helen L. Griggs, then secretary to Nobel Laureate E.0. Lawrence. They now have four children Peter Glenn, Lynne Annette, David Michael, and Stephen Keith.
While still on leave from the University of California, he was promoted from the rank of Assistant Professor to that of full Professor (1945). In May, 1946, he returned to the University of California to assume his position in the Chemistry Department and to take responsibility for the direction of the nuclear chemical research in the Radiation Laboratory of the University.
He attended the California Institute of Technology (B.S. 1928, M.S. 1929) and Princeton University (Ph.D. 1932), and went to the University of California at Berkeley as a National Research Fellow in 1932. After two years as a research fellow and one as a research associate, he became a member of the faculty in the Department of Physics at Berkeley (instructor, 1935; assistant professor, 1936; associate professor, 1941; professor, 1946). He was away on leave of absence from November 1940 to September 1945, engaged in national defense research. He is a fellow of the American Physical Society, was elected to membership in the National Academy of Sciences in 1947, and received the Research Corporation's 1950 Scientific Award in 1951.
His thesis was in the field of molecular beams, and the problem he undertook as a National Research Fellow was the measurement of the magnetic moment of the proton by a molecular beam method; however, after this quantity had been determined elsewhere, he transferred his activities to nuclear physics, entering the Radiation Laboratory of Professor E.0. Lawrence in 1934. There he engaged in studies of nuclear reactions and their products and helped in the design and construction of cyclotrons and other equipment. At that laboratory in 1939 and 1940 he did the work for which he received half of the Nobel Prize in Chemistry for 1951. In 1945, while away from Berkeley on leave of absence, he had the idea of "phase stability", which led to the development of the synchrotron and synchro-cyclotron; these machines have already extended the energies of artificially accelerated particles into the region of hundreds of MeV and have made possible many important researches.
[Dr. McMillan died in 1991]
© the Nobel Foundation 1952