Plutonium: A History of the World’S most Dangerous Element by Jeremy Bernstein

Author:Jeremy Bernstein
Language: eng
Format: epub
Tags: Explore Science. Science : Past and Future. Math, Chemistry and Physics : Chemistry
Publisher: NATIONAL ACADEMIES PRESS
Published: 2007-03-29T16:00:00+00:00

We would have to develop this process for an element that now [in 1942] existed in such minute amounts that no one had ever seen it. All our knowledge of it was based on the secondary evidence of tracer chemistry—measurements of radioactivity and deduced reactions. Tracer chemistry was itself relatively new; deductions based on it were often subject to doubt. 21

Seaborg’s first task was to recruit other scientists; however, several handicaps stood in the way of this endeavor. In the first place, he did not have a significant scientific reputation. His greatest discovery up to that point was plutonium and this was a secret. In the second place, he could not tell a potential recruit what the project was until the individual was aboard and cleared. In his autobiography, Seaborg describes discussing the job in very vague terms with a chemist that he was trying to recruit. The chemist said that the details didn’t matter since whatever it was it would involve the 92 known chemical elements. It was only later that he learned it involved element 94, which he had not known had been discovered. On top of this, Seaborg needed people who specialized in a discipline, extreme microchemistry with radioactive elements (which later came to be called “radioultramicrochemistry”), that at the time did not exist.

Despite these handicaps, Seaborg rapidly assembled a group. He must have been a very charismatic leader. The average age of the group was 25. No one was allowed to use the name plutonium, or even element 94, so they devised a code. The element was called “49,” because it had an atomic number of 94 and an atomic mass of 239. This code, which was also applied to other elements (for example, uranium-235 became known as 25) was used throughout the war, even at Los Alamos. I leave it to the reader to decide the efficacy of this attempt at concealment.

Seaborg knew from the work he had already done at Berkeley that plutonium, like uranium, had stable oxidation states, that is, atomic states in which some number of electrons have been removed from the atom by putting it in contact with an element, such as fluorine, that grabs electrons. The relevant states for plutonium were the states in which four or six electrons had been removed. The question was how to exploit this property. In the first place one needed plutonium, which at the time came only from cyclotrons. The Berkeley 60-inch cyclotron supplied some plutonium, but most of it came from a cyclotron at Washington University in St. Louis that ran 24 hours a day for a year, irradiating uranium. Seaborg reports that in a year and a half the two cyclotrons produced two milligrams—the size of a grain of salt—of plutonium. Of course it came unseparated from the uranium matrix and the radioactive fission fragments. On one occasion, a truck pulled up from St. Louis with 300 pounds of irradiated uranium that had been packed in such a way that part of the sample had spilled out.

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