Segrè then turned his attention to another missing element on the periodic table, element 85. After he announced how he intended to create it by bombarding bismuth-209 with alpha particles at a Monday meeting Radiation Laboratory meeting, two of his colleagues, Dale R. Corson and Robert A. Cornog carried out his proposed experiment. Segrè then asked whether he could do the chemistry and, with Kenneth Ross MacKenzie, successfully isolated the new element, which is today called astatine. Segrè and Wu then attempted to find the last remaining missing non-transuranic element, element 61. They had the correct technique for making it, but lacked the chemical methods to separate it. He also worked with Seaborg, McMillan, Joseph W. Kennedy and Arthur C. Wahl to create plutonium-239 in Lawrence's cyclotron in December 1940.