Assisting Seaborg's Research, Discovery of Uranium-233
|GOFMAN:||I was terrified-"Get your research started." I didn't think I knew anything to get started in research. I figured you'd take courses for at least a year or so. The system at Berkeley-I don't think it's different now-was [that] you went around as a graduate student to see professors to see if they had something that they wanted a new student to work on with them. I finally narrowed it down to seeing William Francis Giauque. Low-temperature thermodynamics-[it] looked like interesting work. The other [choice] was this young guy who was an assistant professor, I think, at the time: Glenn Seaborg.|
|GOURLEY:||Oh, there's a name.|
|GOFMAN:||So, I chose to work with Glenn Seaborg. I did get started on my research within a couple of weeks.|
|GOURLEY:||What specific research were you working on with Glenn Seaborg?|
|GOFMAN:||The specific research was the one hole in a series of radioactive nuclides.
That was called the "4n+1" if you divide the atomic mass number by
four. They had [radionuclide] members with [zero] things added and things with
two, three and four added, but no "4n+1." Seaborg said, "Maybe we
can find out why this is missing." That was [the] year after fission was
discovered. Before the discovery of fission, somebody had thought they had seen
protactinium-233, which was in that [4n+1] series. When fission was discovered,
they no longer knew whether they had a protactinium or didn't, because there was
a zirconium nuclide that would have the same chemical properties as
protactinium. They weren't sure anymore whether protactinium existed in this one
[series] they had thought they made before the discovery of fission.
The first start of the work was to bombard thorium with neutrons that made thorium-233 from thorium-232. It was very short-lived for [an] isotope: 23 [minutes' half-life, decaying by beta emission to protactinium]. This radioactivity had a 27-day half-life [and] the properties, either of zirconium or protactinium. Very little was known about the chemistry of element 91 (which [is] protactinium) at that time. Except it was known that it did have some chemical properties similar to zirconium.
I remembered I had gotten as far as Christmas Day in 1940 where I was able to crystallize zirconium oxychloride in a concentrated hydrochloric acid, show[ing] that the radioactivity did not go with the zirconium [but] was left over after I crystallized away the zirconium. Therefore it was protactinium-233. We fully published [this finding] in Physical Review with Seaborg, [me,] and Joe Kennedy. [Do] you know Joe Kennedy?
|GOFMAN:||Joe Kennedy was one of the most brilliant chemists I've ever met. He [was] working with Seaborg. He was the guy who did all the equipment manufacture for our group. There were no scaling circuits, there were no counters, no nothing. Joe built them, and in fact some commercial companies grew out of some of the things he developed. He was a chemist with golden hands and very brilliant. Ernest Lawrence knew it, and so when things went a little further Joe split away from our group because Ernest needed him to work on the 234U and 235U separation of the electromagnetic method for the war, the bomb.|
|GOFMAN:||Then a little later, Joe was tapped by J. Robert Oppenheimer to be the
chief chemist at the Los Alamos Lab. But in the early days, Joe helped get us
started. The next step, since protactinium decayed by a beta emission, [was
that] there had to be uranium-233 because that's what you get [from] the
protactinium [decay] one unit higher on the periodic table. The idea was to look
for uranium-233. By then, we knew about fission. There was talk about a possible
So the question was, "what kind of properties would 233U have?" We didn't know whether it would have a half-life of 5 days or 100,000 years. I started to look for alpha particles growing out of the protactinium samples. It was just marginal that there was some alpha [emission] growing out with a very long half-life. It was so marginal we couldn't be sure. We knew we needed a much bigger bombardment of thorium to try to make more.
Summertime came, school was over in May (at that time it started in August; I think it's back to that system now). So, we had no support, no monetary support, it was just little support.
|GOURLEY:||This was at Berkeley with Seaborg?|
|GOFMAN:||Yes, and I said I sure would like to stay for the summer. [However,] I got
married before I came out to California, and with the teaching assistantship and
65 [dollars] a month, it was possible to live, but there was nothing [(no
income)] for the summer. Seaborg tried to get me a $150 [stipend] for the
summer, which wasn't available. I did have 6 weeks that were taken care of
because I was a lab assistant in Physical Chemistry. But then the last 6 weeks
of summer, there was no support at all, so we went back to Ohio to live with our
families. Seaborg has written that up in some memoirs of his own; I can't
remember which of the books. He couldn't get $150 for somebody [who] worked on a
program which eventually got labeled a fifty-quadrillion-dollar discovery.
I came back in the fall and all kinds of things were different. By then the Office of Scientific Research and Development was getting more serious and we had money.
|GOURLEY:||Where did the money come from?|
|GOFMAN:||From the Government and the Office of Scientific Research and Development. That was before the Manhattan Project.|
|GOFMAN:||Seaborg even got some money to hire Ray Stoughton, who had just gotten his
Ph.D. a couple years before at Berkeley, to help me with the work. To make a
very long story short, work went fine. Because Seaborg was convinced the work
was important, they even managed to get me absolved of the teaching duties of
being a graduate teaching assistant in the freshman Chemistry class, which had
to be two afternoons a week. Then I had a very good break: I only had to read
papers for Professor Giauque, who was the other person I wanted to work with. I
had taken his course the year before. I really got to understand it the next
year when I was the teaching assistant and I had to read the problem sets on the
exams. He was a great man.
The work went fine; we did get a big bombardment of thorium, let the protactinium decay, and finally concentrated the material down. We put it all on a plate and watched the alpha particles grow out and showed we had uranium-233 with a half-life of about 150,000 years.
|GOURLEY:||Now how dangerous is that?|
|GOFMAN:||Uranium-233 in the amount we had? We had four-millionths of a gram. Not very dangerous.|