Little boy consisted of two masses of Uranium 235 as radioactive material. A "gun-assembly method" ignited the bomb as follows: one subcritical mass of uranium was fired at another, and together they reached a critical mass to set off a nuclear explosion. | Little boy consisted of two masses of Uranium 235 as radioactive material. A "gun-assembly method" ignited the bomb as follows: one subcritical mass of uranium was fired at another, and together they reached a critical mass to set off a nuclear explosion. |