Bretscher and Feather argued, on theoretical grounds, that this element might be capable of fission by both fast and slow neutrons like uranium-235. If so, this promised another path to an atomic bomb, as it could be bred from the more abundant uranium-238 in a nuclear reactor, and separation from uranium could be by chemical means, as it was a different element, thereby avoiding the necessity for isotope separation. Kemmer suggested that since uranium was named after the planet Uranus, element 93 could be named neptunium and 94 plutonium after the next two planets. Later it was discovered that the Americans had independently adopted the same names, following the same logic. Bretscher and Feather went further, theorising that irradiation of thorium could produce a new isotope of uranium, uranium-233, which might also be susceptible to fission by both fast and slow neutrons. In addition to this work, Eric Rideal studied isotope separation through centrifugation.