First sample of Plutonium-239, in Seaborg's "Cigar Box", used to determine its fission properties. On April 19, 1942, Glenn T. Seaborg reached Chicago and joined the chemistry group at the Metallurgical Laboratory of the Manhattan Project at the University of Chicago, where Enrico Fermi and his group would later convert uranium-238 to plutonium-239 in a controlled nuclear chain reaction. Seaborg's role was to figure out how to extract the tiny bit of plutonium from the mass of uranium. Plutonium-239 was isolated in visible amounts using a transmutation reaction on August 20, 1942, and weighed on September 10, 1942, in Seaborg's Chicago laboratory. He was responsible for the multi-stage chemical process that separated, concentrated and isolated plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in nuclear reactors, along with uranium-235 and uranium-233. Plutonium-239 has a half-life of 24,110 years.