When putting uranium with neutrons would cause instability in the uranium nucleus. This would split in which mass was lost and was converted into kinetic energy. They had discovered what had opened pandora box. "when each of the neutrons go into a uranium nucleus and each successful generation which has more neutrons which causes an explosive chain reaction. When two masses of uranium one in the shape of a plug and the other a sphere come together with sufficient speed inside of a bomb and exponential increasing explosion force would result. The scientist knew that with out a doubling action inside of the uranium could not happen the bomb would not be able to work or do anything as so they wished.