Abbreviation for "Hydrogen
Bomb". The hydrogen
bomb is the big brother of the first nuclear bombs, Fat Man and Little Boy, which were dropped on Nagasaki and Heroshima in 1945.
The hydrogen
bomb uses a hydrogen neutron, fired at high speed, into an atom of some unstable element, usually uranium. This causes the uranium particle to separate. This, in turn, releases alot of enegry. The
two halfs then proceed to re-do the above steps in a Chain Reaction, which is called fission.
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EDIT: Actually it fuses together the neutrons of hydrogen in a thermonuclear reaction, not split apart the uranium.
Usually with a blast diameter of 10+
miles, as opposed to 1 mile diameter for an A
bomb.