What is the full name of the man that met with the person who had worries about pure plutonium at the Los Alamos Laboratory in 1943?
The breakthrough with plutonium was by Bretscher and Norman Feather at the Cavendish Laboratory. They realised that a slow neutron reactor fuelled with uranium would theoretically produce substantial amounts of plutonium-239 as a by-product. This is because uranium-238 absorbs slow neutrons and forms a short-lived new isotope, uranium-239. The new isotope's nucleus rapidly emits an electron through beta decay producing a new element with an atomic mass of 239 and an atomic number of 93. This element's nucleus also emits an electron and becomes a new element with an atomic number 94 and a much greater half-life. Bretscher and Feather showed theoretically feasible grounds that element 94 would be fissile—readily fissioned by both slow and fast neutrons, with the added advantage of being different from uranium, and therefore could be chemically separated from it. Bretscher even devised a chemical method to separate.This new development was also confirmed in independent work by Edwin M. McMillan and Philip Abelson at Berkeley Radiation Laboratory also in 1940. Nicholas Kemmer of the Cambridge team 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 fortuitously suggested the same names. The production and identification of the first sample of plutonium in 1941 is generally credited to Glenn Seaborg, using a cyclotron rather than a reactor at the University of California. In 1941, neither team knew of the existence of the other.Chadwick voiced concerns about the need for such pure plutonium to make a feasible bomb. He also suspected that the gun method of detonation for a plutonium bomb would lead to premature detonations due to impurities. After Chadwick met Robert Oppenheimer at the Los Alamos Laboratory in 1943, he learned of a proposed bomb design which they were calling an implosion. The sub-critical mass of plutonium was supposed to be surrounded by explosives that were arranged to detonate simultaneously. This would cause the plutonium core to be compressed and become supercritical. The core would be surrounded by a depleted uranium tamper which would reflect the neutrons back into the reaction, and contribute to the explosion by fissioning itself. This design solved Chadwick's worries about purity because it did not require the level that would be needed for the gun-type fission weapon. The biggest problem with this method was creating the explosive lenses. Chadwick took this information with him and described the method to Oliphant who then took it with him to England.
Robert Oppenheimer