Fission bombs worked, but they weren't very efficient. Fusion bombs, also called thermonuclear bombs, have higher kiloton yields and greater efficiencies than fission bombs. To design a fusion bomb, some problems have to be solved:
First, to store deuterium, the gas could be chemically combined with lithium to make a solid lithium-deuterate compound. To overcome the tritium problem, the bomb designers recognized that the neutrons from a fission reaction could produce tritium from lithium (lithium-6 plus a neutron yields tritium and helium-4; lithium-7 plus a neutron yields tritium, helium-4 and a neutron). That meant that tritium would not have to be stored in the bomb. Finally, Stanislaw Ulam recognized that the majority of radiation given off in a fission reaction was X-rays, and that these X-rays could provide the high temperatures and pressures necessary to initiate fusion. Therefore, by encasing a fission bomb within a fusion bomb, several problems could be solved.
- Deuterium and tritium, the fuel for fusion, are both gases, which are hard to store.
- Tritium is in short supply and has a short half-life, so the fuel in the bomb would have to be continuously replenished.
- Deuterium or tritium has to be highly compressed at high temperature to initiate the fusion reaction.