Zone refining of plutonium metal

An experiment demonstrated the possibility of developing a zone refining process that would produce the first plutonium metal of extremely high purity. Plutonium rods containing known amounts of impurities were melted inside tantalum boats and passed horizontally through a three-turn, high-frequency coil so as to cause a narrow molten zone to pass through each rod 10 times. The impurity elements cobalt, chromium, iron, nickel, neptunium, and uranium moved in the same direction as the molten zone, as predicted; the elements aluminum, americium, and gallium moved in the opposite direction of the molten zone, as predicted. As the impure alloy was zone refined, δ-phase plutonium metal crystals formed.