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The Mystery of Glenn Seaborg's Missing Plutonium: Solved
KentuckyFC writes: In the early 1940s, Glenn Seaborg made the first lump of plutonium by bombarding uranium-238 with neutrons in two different cyclotrons for over a year, The resulting plutonium, chemically separated and allowed to react with oxygen, weighed 2.77 micrograms. It was the first macroscopic sample ever created and helped win Seaborg a Nobel prize ten years later. The sample was displayed at the Lawrence Hall of Science in Berkeley until the early naughties, when it somehow disappeared. Now nuclear detectives say they've found Seaborg's plutonium and have been able to distinguish it from almost all other plutonium on the planet using a special set of non-destructive tests. The team says the sample is now expected to go back on display at Seaborg's old office at Berkeley.
the early naughties, those were the good ole days.
They looked at the radiation coming out of the sample to find evidence of Am-241, an impurity that would be formed if the sample were created in a cyclotron but not if it were created in a reactor. This test doesn't require the sample even to be touched.
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It's the other way around. Extra neutron captures in plutonium created in a nuclear power reactor produces Pu-241 and by decay, Am-241. The bombardment of U-238 with deuterons doesn't produce Pu-241. No Am-241 in the sample hence it was not produced in a reactor. That's the theory.
It's more complicated than that, there are ways of producing very pure Pu-239 in a reactor but the extreme purity of the sample in question seems to mitigate against it being produced by the capture of fission neutrons in a reactor.
And Pu-239 has a half life of 24,100 years.
I was honored to know Glenn Seaborg while working at Lawrence Berkeley Labs in the 1980's. By then, Manhattan Project was long behind him, as was his Nobel prize, the Atomic Energy Commission work, and his chancellorship of the University of California. Yet he was still a kind and supportive scientist who was deeply interested in any research - whether in physics, astronomy, chemistry, or biology. He recognized the need to teach music and art alongside science and math, and would visit local high schools to encourage students.
I once met him at the Lawrence Hall of Science, walking around the old cyclotron. When I asked him about it, he said that he'd been wondering how the field magnets had been mounted (it was perhaps 40 years after the Manhattan Project). After a short chat he invited a few 12 year old kids over, and told stories about using the beast to create new elements. Amazing guy.