 This competition ended abruptly when Segrè's group at Los Alamos discovered that high levels of a hitherto undiscovered plutonium-240 isotope in reactor-produced plutonium meant that an implosion-type nuclear weapon was required, and a high degree of purity was therefore unnecessary.Kennedy's chemists were able to reduce uranium hydride to uranium-235 metal with 99.96% efficiency, and the metallurgists worked out how to cast and press it into the required shapes.While the chemists worked out how to purify plutonium, the metallurgists had to figure out how to cast it into a solid sphere.