 An early debate among the scientists was whether the fissile material for an atomic bomb should be uranium-235 or plutonium.Tube Alloys had performed much of the pioneering research on gaseous diffusion for uranium enrichment, and Oliphant's team in Berkeley were well-acquainted with the electromagnetic process.The staff that had remained in Britain strongly favoured uranium-235; but the scientists that had worked in the United States argued for plutonium on the basis of its greater efficiency as an explosive, despite the fact that they had neither the expertise in the design of nuclear reactors to produce it, nor the requisite knowledge of plutonium chemistry or metallurgy to extract it.