The most powerful of all bombs is known to be the “Atomic bomb” based on nuclear fission of elements like Uranium and Plutonium. The pure fission bombs release massive amounts of energy by splitting atomic nuclei in a supercritical chain reaction. They are the most daunting that swallowed 200,000 lives when dropped on Hiroshima and Nagasaki.
There are two types of such a bomb, one is the Gun type, that explodes a ball of enriched nuclear material into another with such force that it causes a nuclear chain reaction. The other Implosion-type achieves nuclear fission with more accuracy and efficiency by collapsing a hollow sphere over a core of nuclear material. The image by Reuters shows an illustration of both. Interestingly the Fat man bomb dropped over Nagasaki was implosion type while the Little Boy that detonated over Hiroshima was the gun-type.
The thermonuclear bomb, what is more commonly known as a hydrogen bomb releases a much greater amount of energy than a nuclear bomb could. The hydrogen bomb is a fusion bomb that is triggered by a nuclear reaction. The nuclear fission reaction releases a powerful blast of X-rays that sets off the fusion bomb. As the X-rays travel at speed much faster than that of the shock-wave, there is no risk of damage to the hydrogen bomb setting. H-bomb uses the energy from the fission reaction to combine atomic nuclei thus causing another much more humongous energy blast. The reason they are called hydrogen bombs is that the two merging nuclei are usually deuterium and tritium which are isotopes of hydrogen.
In summary, an atomic bomb is the basis of nuclear fission, while a hydrogen bomb forms the foundation of a nuclear fusion reaction requiring massive amounts of energy. The energy is the result of a nuclear fission reaction or simply an atomic bomb. However, it is possible to make a pure fusion based bomb in theory, but it has not invented yet.
A fusion bomb can cause thousands of times more destruction that the real atomic bomb but they can be designed to produce less radiation as well. By suppressing the explosive yield of a hydrogen bomb and maximizing the radioactive neutron output, we get a neutron bomb that can be as deadly as hell. Such a bomb can wipe out an entire population while leaving the infrastructure intact. The effects also disperse fairly quickly.
America’s Castle Bravo H-bomb in 1954 is the country’s biggest test to date with an effect of 15,000 kilotons of TNT.
The Castle Bravo was the largest in America, but a Soviet H-bomb Tsar Bomba, tested in 1961 had registration as an equivalent of 50,000 kilotons of TNT.
According to an estimate, there are nearly 14,900 nuclear weapons in the world which are more than enough to destroy the entire planet. Due to disarmament programs, the number has reduced to about one-third since the 1980s. What matters more is what would happen if a nuke got into the wrong hands and the risk of that happening is not zero.