How Does An Atomic Bomb Work?

A critical mass of enriched Uranium-235 is divided into several parts of a sphere. Behind each part is a conventional explosive device. When the bomb is triggered, the explosives are detonated simultaneously, and the Uranium is driven together to form a sphere of greater than critical mass. At this point, the fission forms a self-sustaining chain reaction which releases large amounts of energy, typically equivalent to several thousand tons of TNT. That's a fission bomb, or A-Bomb. Surround that bomb with fusion fuel such as Tritium or Deuterium, and the fission reaction can superheat the fuel to cause a fusion reaction, releasing lots of high-speed neutrons which can create fission in otherwise stable materials and release enormous amounts of heat. This is the thermonuclear bomb, or H-bomb (the H is because Tritium and Deuterium are isotopes of Hydrogen)