It was completely unexpected, a most extraordinary event that mimicked the r-process by which the heaviest elements were put on our Earth in the first place.
Early next morning, I sought out Thompson and told him of my crazy idea. He was immediately enthusiastic and said that with very simple chemistry he could extract a transcalifornium fraction in a couple of days. He thought that he could get a sample of the debris from Ken Street, who, as Thompson's Ph.D. student, had helped us discover element 98 a couple of years before. Since then, Street had been hired by the Livermore Laboratory to set up a diagnostic group there, and they had received a filter paper from the test (code-named Mike) to practice their techniques.
This was an exciting moment. Would we find anything at all? Almost immediately, I saw 6.6-MeV -particles in the transcalifornium fraction, an energy that I had never seen before! And the intensity was about 1 c/m. This was eerie. Could this be the element 100 that my guesstimate had predicted?
Because of the imprecision of the first chemical separation, we did not know whether the 6.6-MeV -particles came from element 99 or from 100, so further experiments were performed, this time with the inclusion of a Cf-246 tracer. These showed conclusively that the new element that we were observing had the atomic number 99. After following its decay for a few weeks, we knew that its half-life was about a month.
These startling results were communicated to Los Alamos and Argonne, and now we were bona fide members of the team. The next order of business was to look for element 100. For that we would need more material from the test, since we knew that its yield would be much smaller. This was obtained from fallout that had settled on the coral of a neighboring island. Barrels of the highly radioactive material were flown to the U.S., and in short order, Thompson set up a small chemical processing plant and proceeded to isolate an element-100 fraction. Once again, we were surprised to find a small amount of a new activity, 7.1-MeV -particles with a half-life of only a day. It had been about two months since the explosion; they had been kept alive by a -emitting isotope of element 99 with a half-life of about a month.
By September 1953, the three laboratories--Berkeley, Argonne, and Los Alamos--had established with certainty the mass assignments of isotopes of elements 96-100 that had been generated by the Mike explosion, but there was no indication as to when this information might be declassified so that it could be published. We became concerned that other, lighter isotopes of elements 99 and 100 might be discovered by heavy-ion reactions and these would not be classified secret and could be published. Not being aware of our work, these discoverers, of course, would want to name these elements, since this signal honor traditionally goes to the people who first find them. It was not clear that our secret work would be recognized as having priority, so we decided to forestall this problem by investigating these heavy-ion reactions ourselves.
Bombardments of U-238 with N-14 ions produced by the Crocker Laboratory cyclotron did produce a short-lived light isotope of element 99 that we were able to isolate chemically, so we published the work as due to element 99. When we published this experiment in 1954, we indicated that there was prior research on this element that had not yet been declassified, so that our heavy-ion work did not constitute the discovery of element 99.
At about the same time, something similar happened in the case of element 100. When we examined the products of the long neutron bombardments of Pu-239, as expected, we found 99-253, the same isotope that we had discovered in the Mike research. When this material was bombarded with neutrons at the MTR high-flux reactor in Idaho, we found a short-lived new -emitting isotope, 99-254. This activity decayed to -emitting 100-254, which we were able to isolate chemically. Since this research was not secret, we were able to publish it immediately. Again, it was accompanied with a disclaimer that said that there was prior work on element 100.
With this incentive, the Mike work was declassified and the discovery of elements 99 and 100 was published by the large team of scientists from Berkeley, Argonne, and Los Alamos. At this time, I suggested that we should start a new paradigm and name new elements after famous scientists. A natural choice that was strongly supported by everyone was einsteinium for element 99 and fermium for element 100, and I had the honor of announcing this selection at the Geneva International Conference on the Peaceful Uses of Atomic Energy in 1955.
A more detailed description of this amazing episode in science can be found in Chapter 6 of "The Transuranium People: The Inside Story" by Darleane C. Hoffman, Albert Ghiorso, and Glenn T. Seaborg (Imperial College Press, 2000)
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