 The feasibility of a plutonium bomb was questioned in 1942 . James Conant heard on 14 November from Wallace Akers , the director of the British " Tube Alloys " project , that James Chadwick had " concluded that plutonium might not be a practical fissionable material for weapons because of impurities . " Conant consulted Ernest Lawrence and Arthur Compton , who acknowledged that their scientists at Berkeley and Chicago respectively knew about the problem , but could offer no ready solution . Conant informed the director of the Manhattan Project , Brigadier General Leslie R. Groves , Jr . , who in turn assembled a special committee consisting of Lawrence , Compton , Oppenheimer , and McMillan to examine the issue . The committee concluded that any problems could be overcome simply by requiring higher purity . 
