Harrison Brown and the Isolation of Plutonium

Two pellets of Plutonium (photo: U.S. Department of Energy)

Two pellets of Plutonium (photo: U.S. Department of Energy)

On September 26, 1916, American nuclear chemist and geochemist Harrison Scott Brown was born. Brown is generally known for his role in isolating plutonium for its use in the first atomic bombs and for his studies regarding meteorites and the Earth’s origin. He also was a political activist, who lectured and wrote on the issues of arms limitation, natural resources and world hunger.

Harrison Brown was born in Sheridan, Wyoming, USA, the son of Harrison H. Brown, a rancher and cattle broker, and Agnes Scott Brown, a piano teacher and a professional organist. His father died when he was ten years old, and mother and son moved to San Francisco. Harrison grew up to be a competent pianist, who organized his own jazz orchestra. After graduating from Galileo High School in San Francisco, he entered the University of California at Berkeley, and received a B.S. in chemistry in 1938. Brown followed his mentor Robert D. Fowler, who interested him in nuclear chemistry, from Berkeley to Johns Hopkins University as a graduate student. For his doctoral studies, Harrison developed mass spectrometric techniques for studying the isotopic composition of cobalt as part of the development of knowledge concerning relative stabilities of nuclides, and of the more general case of occurrences of nuclear species in solar nebula formed from nuclear reactions in stars.[1]

With the discovery of nuclear fission in 1939, Brown and Fowler devoted their attention to the diffusion properties of uranium hexafluoride. Within a year they found themselves with the largest gaseous uranium fluoride generating capacity in the United States and became major suppliers of uranium tetrafluoride and hexafluoride for the atomic fission projects initiated at Columbia University
and the University of Chicago.[1]

In 1942 Glenn T. Seaborg, whose involvement in the synthesis, discovery and investigation of ten transuranium elements later earned him a share of the 1951 Nobel Prize in Chemistry, invited Brown to work with him at the University of Chicago in the Manhattan Project’s Metallurgical Laboratory, working on ways to separate plutonium from uranium. The Manhattan Project intended to create plutonium by irradiating uranium in a nuclear reactor. The resulting highly radioactive product would then have to be chemically separated from the uranium and any fission products created by the irradiation process. The problem was that plutonium was a new element with chemical properties that were not yet fully known. Until a reactor could be built, it was available only in microgram amount, so an industrial separation process would have to be scaled up one billion times. With Orville Hill, Brown devised a successful method of achieving this by using the gaseous evaporation of fluorides.

Brown and some of his colleagues relocated to the Oak Ridge, Tennessee, to work with the X-10 Graphite Reactor at Clinton Engineer Works,where he became the assistant director of chemistry. Working with the reactor there, they developed the separation processes for producing kilogram quantities of plutonium. The techniques discovered by the team proved to be the groundwork for those used at the Hanford Site which provided the plutonium for the Fat Man bomb dropped on Nagasaki on August 9, 1945. After the two atomic fission bombs were exploded and the war with Japan ended, Harrison joined other Manhattan Project scientists in expressing their grave concern about the future, for no matter what strong justifications for their involvement in the bomb project may have been during the war, they felt powerfully committed to do things that would help rectify existing social evils.[1] Just four months later he completed Must Destruction Be Our Destiny? (1945), a book detailing the dangers of nuclear weapons as well as the dangers of an arms race. To promote it he traveled widely, giving 102 lectures within three months.[3]

In 1946, Brown returned to the University of Chicago to work as an assistant professor of Chemistry in the Institute for Nuclear Studies. He was joined by some of his former colleagues from the Manhattan Project and together they became the first team to study nuclear geochemistry. He went on to study meteorites and planetary structures along with ways to date the age of the Earth, encouraging George Tilton and Clair Cameron Patterson to investigate the isotopic composition of iron meteorites. His report, Elements in Meteorites and the Earth’s Origin, won an award of the American Association for the Advancement of Science for the most outstanding contribution in that field in 1947.[3] Patterson’s studies of lead eventually led to the first close approximation of the age of the Earth and the solar system of 4.5 billion years.[2] In 1948 Brown was awarded the American Association for the Advancement of Science prize for his work on meteorites. Nuclear mass abundance data from Brown’s research helped Maria G. Mayer develop the concept of the nuclear shell model.[5,6]

Between 1951 and 1977, Brown was professor of geochemistry at the California Institute of Technology (Caltech), where he attracted several former colleagues and highly regarded scientists to the team. Together they made advancements in telescopic instrumentation, jet propulsion (contributing to NASA’s early planetary exploration missions), and infrared astronomy. Brown joined the National Academy of Sciences in 1955 and was appointed as their foreign secretary in January 1962, a role that he would hold until 1974. During that time he wrote in his next three books: The Challenge of Man’s Future (1954), which dealt with the crisis arising from population growth in a world with limited resources, The Next Hundred Years (1957) and The Human Future Revisited (1978).

Brown was appointed first director of the Resource System Institute at the East-West Center (EWC) in Honolulu. Located adjacent to the University of Hawaii campus in Manoa, the EWC was a research and educational institution focused on problems in the Asia-Pacific Region. He put together a team of scientists from across the US to follow through even more directly on the ideas he developed in his books, i.e. to explore the sustainability of energy, minerals, and food systems and how they interacted with population and environment.

In 1983, in failing health, Brown retired and moved to Albuquerque, New Mexico. Harrison Brown died on December 8, 1986, aged 69.

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