 In 1940, when Egon Bretscher and Norman Feather showed that a slow neutron reactor fuelled with uranium would in theory produce substantial amounts of plutonium-239 as a by-product, Kemmer (who was lodging at the Bretschers') proposed the names Neptunium for the new element 93 and Plutonium for 94 by analogy with the outer planets Neptune and Pluto beyond Uranus (uranium being element 92).The Americans Edwin M. McMillan and Philip Abelson at the Berkeley Radiation Laboratory, who had made the same discovery, fortuitously suggested the same names.He spent 1944–1946 in Canada.