Arthur C. Wahl, who contributed widely in the field of nuclear and radiochemistry and, as a graduate student, discovered plutonium, died on March 6, 2006 of Parkinson's disease and pneumonia.
Art was born Sept. 8, 1917 in Des Moines, Iowa. In 1939 he received his Bachelor's Degree in chemistry from Iowa State University. He went to Berkeley for graduate work where he chose to work with Joseph W. Kennedy and Glenn T. Seaborg, to isolate and chemically identify element 94, later named plutonium. Art purified element 93 (later called neptunium) produced by bombardment of uranium with deuterons (d,2n). From the decay of the 2.1-day 238 93Np Art, with the aid of detectors built by Kennedy, observed the growth of a long-lived alpha activity. This activity was growing in with a rate characteristic of the half-life of 238 93Np. The radiochemical similarity of this alpha activity with thorium demanded that an unambiguous separation from Th be made before assigning it to element 94 (238Pu). Art was trying to identify element 94 by oxidizing it to a higher oxidation state than the IV of thorium. At about midnight Feb. 24, 1941, Art working alone in Room 307 of Berkeley's Gilman Hall, managed to show that the highest oxidation state of the new alpha activity did not follow the beta-emitting tracer 234Th (UX1). This proved that the new alpha activity was indeed from a new element.
Subsequently Art, now working with Kennedy, Seaborg and Emilio Segré, purified 239 94Pu from 1.2 Kg of uranium oxide, which had been irradiated for two days with neutrons. The purified sample showed another long-lived alpha activity growing in with the known 2.3-day half-life of 239 93Np. The 0.5 microgram sample of 239 94Pu, prepared by Art with very little carrier and now in the Smithsonian as Sample B , was shown to be fissionable with slow and fast neutrons.
Art received his PhD degree in 1942 for the plutonium identification. The papers, related to this work were withheld from publication until after the conclusion of the war. From 1943-1946 Art was the leader of the group working on plutonium chemistry at Los Alamos. He developed the Pu chemistry and purification procedures central to the success of the Manhattan Project and used on an industrial scale during and long after World War II.
After the war, A.H. Compton recruited Kennedy to chair the chemistry department at Washington University in St. Louis. Kennedy's condition for acceptance was that he could bring Art and 4 other members of the Los Alamos chemistry group (Lindsay Helmholz, David Lipkin, Herb Potratz, and Sam Weissman) with him.
Art anchored both the inorganic and nuclear chemistry groups at Washington University for almost 4 decades during which time he graduated 35 Ph.D. students. His two long-standing interests were in oxidation-reduction chemistry and fission yields. Art, as much as any other chemist in the 50's and 60's, advanced the techniques used to study electron transfer rates in aqueous solutions. The Wahl fission systematics have been, and are likely to remain forever, the base reference for both basic and applied uses of fission. In the former category are the many exotic beam facilities presently being planned, which make use of accelerated fission fragments.
As a teacher, Art Wahl defined quality. His course in inorganic chemistry, the chemistry of the elements, is legendary for its completeness, his scholarly style, and its capability for making chemists of those who took it. Art also particularly excelled in teaching introductory laboratory courses. Colleagues note that he had no peer as a bench-chemistry teacher. In his hands, inorganic substances invariably reacted with textbook clarity. Any puzzled student who obtained a lesser result was soon advised to add just the right drop of acid, base, oxidizer, reducer, or complexing agent to bring the reaction to heel. Students also were inspired to hear about the color of a plutonium compound from the first person in the world to have seen it. Art also exerted his influence by example, not precept. He said not one word about intellectual honesty or scientific integrity. They were simply in his aura. Already co-discoverer of an element and a famous chemist in his twenties, he nev! er was driven or imprisoned by personal ambition.
In 1991 Art moved back to Los Alamos and continued working, publishing his last fission compilation in 2005. We are but a few of those who hold our memories and friendship with Art as precious.
