 This had been considered by Oppenheimer and Seaborg the month before, and the latter had calculated that neutron emitters like boron had to be restricted to one part in a hundred billion.There was some doubt about whether a chemical process could be developed that could ensure this level of purity, and Chadwick brought the matter to the S-1 Executive Committee's attention for it to be considered further.Four days later, though, Lawrence, Oppenheimer, Compton and McMillan reported to Conant that they had confidence that the exacting purity requirement could be met.