A hydrogen bomb is, by far, the most destructive weapon that mankind has ever invented. It is the most powerful type of nuclear bomb, in some cases reaching more than 2,000 times the yield of the nuclear bombs dropped on Hiroshima and Nagasaki, Japan. Unlike the first “atom bombs” — also known as A-bombs — which release energy by fission, or breaking apart, of heavy atomic nuclei like uranium and plutonium, a hydrogen bomb releases energy by fusing together light nuclei like tritium or deuterium, converting even more matter into energy. When President Truman authorized the dropping of the A-bomb on Hiroshima and Nagasaki, he said that the weapons used the same power as the Sun, but that was not actually true — the Sun uses nuclear fusion, not nuclear fission. A hydrogen bomb, however, really does release the power that fuels the Sun.
How it Works
Nuclear fusion involves creating heavier elements out of lighter ones by joining atomic nuclei together. In the Sun, this mostly takes the form of fusing hydrogen nuclei to form helium. A fusion reaction is very difficult to start because nuclei are positively charged, and therefore strongly repel one another through the powerful electromagnetic force. The nuclei of elements heavier than hydrogen are held together by the strong nuclear force, which, at this scale, is much stronger than the electromagnetic. The strong force, however, is only significant over extremely short distances, of around the size of an atomic nucleus.
To start nuclear fusion, nuclei must somehow be brought very close together. In the Sun, this is achieved by gravity. In a hydrogen bomb, it is achieved by a combination of extreme pressure and temperature brought about by a fission explosion. A hydrogen bomb is therefore a two-stage weapon: an initial fission explosion causes a fusion explosion. A fission bomb "primary" is detonated in the normal way, which then compresses a fusion fuel "secondary" and ignites a uranium "spark plug" which fissions and subjects the fusion fuel to the heat necessary to begin the reaction — about 20,000,000°F (11,000,000°C).
In the Sun, the main fusion process results in four hydrogen nuclei, which consist simply of a single proton, combining to make a helium nucleus, which has two protons and two neutrons. The heavier hydrogen isotopes deuterium and tritium, with one and two neutrons, respectively, are created at intermediate steps. It is impractical to try to replicate the whole process by starting with ordinary hydrogen, but the fusion of deuterium and tritium can be achieved. An early test involved using these gases in liquefied form, but a crucial modification was the use of the solid lithium deuteride, a compound of lithium and deuterium. Under the conditions created by the initial fission explosion, the lithium is transformed into tritium, which then fuses with the deuterium.
The first time the principle of a hydrogen bomb was tested was on 9 May 1951 by the United States military, during the “George” test of Operation Greenhouse at the Pacific Proving Grounds. Most of the energy yield of this test came from fission fuel, but it demonstrated that a fission bomb could be used as a stepping-stone to something even more destructive. A similar test, “Item”, took place on 25 May 1951.
The first true hydrogen bomb test, “Ivy Mike”, was on 1 November 1952, detonated at Eniwetok Atoll in the Pacific, as part of Operation Ivy. The bomb exploded with a force equivalent to 10.4 megatons (million tonnes) of TNT — over 450 times more powerful than the atomic bomb dropped on Nagasaki during World War II. Using liquid deuterium as fuel, this hydrogen bomb required 18 tonnes of refrigeration equipment. It was not a practical weapon, but it proved that a fusion bomb of enormous power could be built.
A later test, “Castle Bravo”, used solid lithium deuteride instead, decreasing the weight of the device, removing the need for refrigeration, and making it a weapon that could be carried by a plane or attached to a missile. The Castle Bravo test, with a yield of 15 megatons, is the most powerful nuclear weapon tested by the United States, but not the most powerful ever. That distinction belongs to the device known as “big Ivan” detonated by the Soviet Union 13,000 ft (4,000 m) above a test field on Novaya Zemlya island on October 30 1961. The 50 megaton explosion resulted in an area of complete destruction with a radius of 15.5 miles (25 km) from ground zero, and broken window panes 559 miles (900 km) away. Witnesses described a huge fireball that reached the ground, and up to a height of almost 34,000 ft (10,363 m); a mushroom cloud that reached 210,000 ft (64,008 m); and a flash that was visible 621 miles (1,000 km) away.