 Oppenheimer brought John von Neumann to Los Alamos in September 1943 to take a fresh look at implosion . After reviewing Neddermeyer 's studies , and discussing the matter with Edward Teller , von Neumann suggested the use of high explosives in shaped charges to implode a sphere , which he showed could not only result in a faster assembly of fissile material than was possible with the gun method , but which could greatly reduce the amount of material required , because of the resulting higher density . The idea that , under such pressures , the plutonium metal itself would be compressed came from Teller , whose knowledge of how dense metals behaved under heavy pressure was influenced by his pre @-@ war theoretical studies of the Earth 's core with George Gamow . The prospect of more @-@ efficient nuclear weapons impressed Oppenheimer , Teller , and Hans Bethe , but they decided that an expert on explosives would be required . Kistiakowsky 's name was immediately suggested , and Kistiakowsky was brought into the project as a consultant in October 1943 . 
