 He used mica sliced razor thin to produce a window to count alpha particle emissions, and ionization chamber with a magnetic field to separate the beta particles from the neptunium from alpha particles from the plutonium.On March 28, 1941, Seaborg, physicist Emilio Segrè and Kennedy were able to demonstrate not only the presence of plutonium, but that it was also fissile, an important distinction that was crucial to the decisions made in directing Manhattan Project research.Arthur Wahl then began exploring the chemistry of the newly discovered element.