307 Gilman Hall . . . Some Reminiscences
by Glenn T. Seaborg
At the dedication of Room 307 Gilman Hall as a National Historic Landmark, University of California, Berkeley, California, Feb.21, 1966
I am happy to participate with Arthur Wahl and Edwin McMillan in this twenty-fifth anniversary of the discovery of plutonium and in the dedication of Room 307 Gilman Hall as a National Historic Landmark.
I imagine it is typical of our times-because of the speed of change, the sheer number of significant events that pile up in the quickly passing years-that each of us today lives through a little more history in our lifetime.
At least this seems to be the case. It is an exciting time to be alive, to be working, to be trying to make some contribution to the scheme of things, and occasionally to have some small success in the effort.
It is also a time when time itself is something of a luxury-particularly time to reminisce. But, since today is a special occasion I hope you will grant me a little of that luxury.
Having a room in which you and your colleagues worked rather routinely, and certainly unceremoniously, designated as a National Historic Landmark is an unusual experience, to say the least. Those of you who remember Room 307 Gilman Hall as it was in those early days (and as it remained for many years) will agree that a less significant or historical looking room hardly existed on the campus of the University of California.
Fortunately the room is still here. It has been enlarged somewhat, and it contains more complicated equipment. The simple small sink, down which some of our precious plutonium was inevitably lost in the course of our experiments 25 years ago, has been replaced by another sink. But the little cubbyhole with its low slanting ceiling directly under Gilman Hall's roof, where we kept our electroscope and various samples, is still an appendage to the room. And it still opens through glass doors to the little outdoor patio where, because of the shortage of laboratory space and fume hoods, we were forced to carry on some of our experiments that gave off noxious fumes. I recall that our counting equipment was two doors down the hall, in Room 303. The alpha radiation ftom the first plutonium was measured in that room, and therefore Room 303 shares a place in history with Room 307. Joseph Kennedy and I had our desks in Room 303, and later, in 1941, one whole wall was taken up with a Chart of Isotopes to which additions and changes were frequently made.
Had Art Wahl, Joe Kennedy, Ed McMillan, or I had the slightest idea that today's event would transpire, we might have looked for more auspicious quarters. I do not think we would have gotten them. Space was at a premium, and we were lucky to have even these rooms to work in. Fortunately we were more interested in getting results in our work than in our surroundings or any significance they might have in the future.
In recalling the story of plutonium, I should go back further, perhaps to 1936, when as a graduate student I spoke in the College of Chemistry weekly seminar, as was required of each of us once a year. Since the fall of 1934, when I began my graduate work at Berkeley, I had been reading first the exciting papers by Fermi, Segre, and coworkers from Rome and then the equally fascinating papers by Hahn, Meitner, and Strassmann from Berlin. They were studying the interesting radioactivities which were produced when uranium was bombarded with neutrons and which they attributed to isotopes of transuranium elements. I remember how I devoured those early papers and how I considered myself something of a minor expert on the "transuranium elements." In fact, they were the subject of my talk at that seminar in 1936, an hour-long talk in which I described those new elements and their chemical properties in great detail. I need not remind you, I am sure, that in January 1939 word reached us that Hahn and Strassmann in Germany had identified the transuranium isotopes as barium lanthanum, and other fission products of uranium and thus established that they were not new elements at all.
During the two years following my seminar talk in 1936 and before the discovery of fission, my interest in the neutron-induced radioactivities in uranium continued unabated and, in fact increased. I read and reread every article published on the subject. I was puzzled by the situation, both intrigued by the concept of the transuranium interpretation of the experimental results and disturbed by the apparent inconsistencies in this interpretation. I remember discussing the problem with Joe Kennedy by the hour, often in the postmidnight hours of the morning at the old Varsity Coffee Shop on the corner of Telegraph and Bancroft Avenues where we often went for a cup of coffee and a bite to eat after an evening spent in the laboratory.
I first learned of the correct interpretation of these experiments, that neutrons split uranium into two large pieces in the fission reaction, at the weekly Monday night seminar in nuclear physics conducted by Professor E. 0. Lawrence in Le Conte Hall. On this exciting night in January 1939, we heard the news from Germany of Hahn and Strassmann's beautiful chemical experiments. I recall that at first the fission interpretation was greeted with some skepticism by a number of those present, but, as a chemist with a particular appreciation for Hahn and Strassmann's experiments, I felt that this interpretation just had to be accepted. I remember walking the streets of Berkeley for hours after this seminar in a combined state of exhilaration in appreciation of the beauty of the work and of disgust at my inability to arrive at this interpretation despite my years of contemplation on the subject.
With those radioactivities identified as fission products, there were no longer any transuranium elements left. However, in later investigations by Ed McMillan at Berkeley and others elsewhere, one of the radioactivities behaved differently from the others. The beta radioactivity with a half-life of about 2.3 days did not undergo recoil. It did not separate from thin layers of uranium when uranium was bombarded with slow neutrons. Mong toward the spring of 1940, Ed began to come to the conclusion that the 2.3-day activity might actually be due to the daughter of the 23-minute uranium-239 and thus might indeed be an isotope of element 93 with the mass number 239 (93-239). Phil Abelson joined him in this work in the spring of 1940, and together they were able to chemically separate and identify and thus discover element 93.
Immediately thereafter, during the summer and fall of 1940, Ed McMillan started looking for the daughter product of the 2.3-day activity, which obviously would be the isotope of element 94 with mass number 239 (94-239). Not finding anything he could positively identify as such, he began to bombard uranium with deuterons in the 60-inch cyclotron in the hope that he might find a shorter lived isotope-one of a higher intensity of radioactivity that would be easier to identify as an isotope of element 94. Before he could finish this project, he was called away to work on radar at M.I.T.
During this time my interest in the transuranium elements continued. Since Ed McMillan and I lived only a few rooms apart in the Faculty Club, we saw each other quite often, and, as I recall, much of our conversation, whether in the laboratory, at meals, in the hallway, or even going in and out of the shower, had something to do with element 93 and the search for element 94. I must say, therefore, that his sudden departure for M.I.T. came as something of a surprise to me - especially since I did not even know when he had left.
In the meantime, I asked Arthur Wahl, one of my two graduate students, to begin studying the tracer chemical properties of element 93 with the idea that this might be a good subject for his thesis. My other coworker was Joe Kennedy, a fellow instructor at the University and, as I have indicated, also very interested in the general transuranium problem.
When I learned that Ed McMillan had gone, I wrote to him asking whether it might not be a good idea if we carried on the work he had started, especially the deuteron bombardment of uranium. He readily assented.
Our first deuteron bombardment of uranium was conducted on Dec.14, 1940. What we bombarded was a form of uranium oxide, U3 08, which was literally plastered onto a copper backing plate. From this bombarded material Art Wahi isolated a chemical fraction of element 93. The radioactivity of this fraction was measured and studied. We observed that it had different characteristics than the radiation from a sample of pure 93-239. The beta particles, which in this case were due to a mixture of 93-239 and the new isotope of element 93 with mass number 238 (93-238), had a somewhat higher energy than the radiation from pure 93-239 and there was more gamma radiation. But the composite half-life was about the same, namely, 2 days. However, the sample also differed in another very important way from a sample of pure 93-239. Into this sample there grew an alpha-particle-emitting radioactivity. A proportional counter was used to count the alpha particles to the exclusion of the beta particles. This work led us to the conclusion that we had a daughter of the new isotope 93-238--a daughter with a half-life of about 50 years and with the atomic number 94. This is much shorter lived than the now known half4ife of 94-239, which is 24,000 years. The shorter half-life means a higher intensity of alpha-particle emission, which explains why it was so much easier to identify what proved to be the isotope of element 94 with the mass number 238 (94-238). (Later it was proved that the true half-life of what we had, i.e., 94-238, is about 90 years.)
On Jan.28, 1941, we sent a short note to Washington describing our initial studies on element 94; these data also served for later publication in The Physical Review under the names of McMillan, Wahl, Kennedy, and Seaborg. We did not consider, however, that we had sufficient proof at that time to say we had discovered a new element and felt that we had to have chemical proof to be positive. So, duting the rest of January and into February, we attempted to identify this alpha activity chemically.
Our attempts proved unsuccessful for some time. We did not find it possible to oxidize the isotope responsible for this alpha radioactivity. Then I recall that we asked Professor Wendell Latimer, whose office was on the first floor of Gilman Hall, to suggest the strongest oxidizing agent he knew for use in aqueous solution. At his suggestion we used peroxydisulphate with argentic ion as catalyst.
On the stormy night of Feb.23, 1941, in an experiment that ran well into the next morning, Art Wahl performed the oxidation which gave us proof that what we had made was chemically different from all other known elements. That experiment, and hence the first chemical identification of element 94, took place in Room 307 of Gilman Hall, the room that is being dedicated as a National Historic I,andmark today, 25 years later.
The communication to Washington describing this oxidation experiment, which was critical to the discovery of element 94, was sent on Mar. 7, 1941, and this served for later publication in The Physical Review under the authorship of Kennedy, Wahl, and Seaborg.
Almost concurrent with this work was the search for, and the demonstration of the fission of, the isotope of major importance-94-239, the radioactive decay daughter of 93-239. Emilio Segre' played a major role in this work together with Kennedy, Wahl, and me. The importance of element 94 stems from its fission properties and its capability of production in large quantities. This, of course, is a story of more than Room 307 Gilman Hall. It involves, in addition, the 60-inch cyclotron, the Old Chemistry Building, the Crocker Laboratory, and the 37-inch cyclotron, all of which have by now been removed ftom the Berkeley campus. The 0.5-microgram sample on which the fission of 94-239 was first demonstrated was produced by transmutation of uranium with neutrons ftom the 60-inch cyclotron; it was chemically isolated in rooms in Old Chemistry Building and Crocker Laboratory and in Room 307 Gilman and the fission counting was done using the neutrons from the 374nch cyclotron.
How element 94 eventually got the name plutonium is an interesting story and one worth telling on this occasion. The work was carried on under self-imposed secrecy in view of its potential implications for national security. Following the discovery in February 1941 and well into 1942, we continued, as I have in my talk thus far, to use only the name "element 94" among ourselves and the other few people who knew of the element's existence. But we needed a code name to be used when we might be overheard. Someone suggested "silver" as a code name for element 93, and we decided to use "copper" for element 94. This worked just fine until, for some reason I cannot recall now, it became necessary to use real copper in our work. Since we continued to call element 94 "copper," on occasion we had to refer to the real thing as "honest-to-God copper."
The first time a true name for element 94 seemed necessary was in writing the report to the Uranium Committee in Washington in March of 1942.1 remember very clearly the debates within our small group as to what that name should be. It eventually became obvious to us that we should follow the lead of Ed McMillan, who had named element 93 neptunium because Neptune is the next planet after Uranus, which had served as the basis for the naming of uranium 150 years earlier. Thus we should name element 94 for Pluto, the next planet beyond Neptune. But, and this is a little known story, it seemed to us that one way of using the base Pluto was to name the element "plutium." We debated the question of whether the name should be "plutium" or "plutonium," the sound of which we liked much better. We finally decided to take the name that sounded better. I think we made a wise choice, and I believe it is also etymologically correct .
There was also the matter of the need for a symbol. Here, too, a great deal of debate was engendered because, although the symbol might have been "P1," we liked the sound of "Pu"-for the reason you might suspect. We decided on "Pu," and, I might add, we expected a much greater reaction after it was declassified than we ever received.
Remembering the early days of the discovery and reading some of the early reports and correspondence brings to mind other events and thoughts that make one realize how times have changed. I recall reading the Uranium Committee report Phil Abelson wrote concerning the importance of our experiments. In it he said:
Obviously, the results of these experiments will have a large bearing in the determination of the value of uranium power. It is probable that the cost of isotope separation will be great. The decision to spend perhaps a million dollars on a separation plant may well hinge on the results of these experiments.
A million dollars? The amount seemed astronomical to us at the time. We had no idea that our work would play a major role in a program that would eventually cost more than two billion dollars within a few years.
Only a short time after that Uranium Committee report, I recall that, at E. 0. Lawrence's suggestion, I wrote to Lyman Briggs requesting a contract for some further work that might be done on the measurement of fission cross sections in the uranium and transuranium regions. Among the items listed on my proposal was a request for an assistant, a chemist Ph.D., at the tempting annual salary of $3,000! Another item on that request was the use of the 60-inch cyclotron at a cost of $25 per hour.
But far more dramatic than these personal recollections, and certainly far more important, was the development of plutonium starting with that first identification in 307 Gilman Hall. No other element has seen a similar growth. Our first experiments were done with tracer amounts as small as a picogram (a million millionth of a gram). Within five years our country was producing plutonium in kilogram amounts. The intervening twenty years have seen the production of somewhere between megagram and gigagram amounts-an escalation of a billion billion fold!
What is the significance of the growth of plutonium? What bearing will this element have on our future? As is true with all the power of science and technology at our command today, what will come of plutonium depends on how we (all mankind) choose to use it. I will not dwell on its destructive potential. This is well known by most of us here today and most people around the world-so much so that to many the symbol of the nuclear age is unfortunately one of horror. Perhaps fear of massive destruction will be the deciding factor that will bring men to choose reason rather than conflict in settling their differences. In this case, perhaps it will also be the power of plutonium, used constructively and beneficially, that will help men achieve some of the things essential to world stability, a more widely shared abundance, and a lasting peace.
Let me leave you with this concluding thought: The advent of plutonium, with its potential for war or peace, its possible use for the devastation of this planet or the lifting of all men to new standards of living, sharply brings into focus the major dilemma of our day. Can man, who now holds his destiny in his own hands, act with enough wisdom, patience, and understanding to choose the right path? I believe he can. I believe he will. I know that the years ahead will add strength to this conviction, and I hope that they will give cause to those who pass by Room 307 to stop now and then, recall what took place there, and perhaps recognize the event as one of the small but rewarding moments in a history leading us all to a better and brighter tomorrow.