A hydrogen bomb uses a fission explosion to compress and heat hydrogen isotopes until they fuse, releasing far more energy.
Teller-Ulam design
- A fission bomb (primary) explodes.
- X-rays compress the fusion fuel (secondary), usually lithium deuteride.
- Pressure and heat trigger fusion of hydrogen isotopes.
- Extra neutrons can fission the uranium casing.
Power
Hydrogen bombs are hundreds to thousands of times stronger than fission bombs. The largest ever, the Soviet Tsar Bomba (1961), yielded about 50 megatons.
First test
The US tested “Ivy Mike” in 1952.
History
The first hydrogen bomb test was the “Ivy Mike” detonation by the United States on November 1, 1952, at Enewetak Atoll in the Pacific. It had a yield of about 10.4 megatons, around 700 times the Hiroshima bomb. The Soviet Union tested its first thermonuclear weapon in 1953 and a full scale one in 1955. The UK (1957), China (1967) and France (1968) followed.
Scale
The largest nuclear test was the Soviet Tsar Bomba, detonated on October 30, 1961, with a yield of about 50 megatons, over 3,000 times the Hiroshima bomb. It was a scaled down version of a 100 megaton design.
Effects
Thermonuclear weapons create blast, intense heat and radiation. The Castle Bravo test in 1954 produced a yield of 15 megatons, more than double the predicted one, causing radioactive fallout that contaminated the Marshall Islanders and the crew of the Japanese fishing vessel Lucky Dragon No. 5.
Nuclear stockpiles
As of 2024, about 12,100 nuclear warheads exist worldwide, with around 90% held by the United States and Russia, according to the Federation of American Scientists. Peak stockpile was about 70,000 in 1986.
Treaties
- Partial Test Ban Treaty (1963) banned tests in the atmosphere, in space and underwater.
- Non-Proliferation Treaty (1970).
- Comprehensive Nuclear-Test-Ban Treaty (1996), which has not entered into force.
- New START between the United States and Russia limits deployed strategic warheads to 1,550 each, extended to 2026.
Role in history
Debate over the hydrogen bomb in 1949 to 1950 divided scientists, including J. Robert Oppenheimer, who opposed its development.
Peaceful use of fusion
The same fusion process powers the Sun, and researchers are trying to harness it in a controlled way for electricity.
Mechanism in brief
A thermonuclear weapon uses a fission primary to create the conditions for fusion of hydrogen isotopes in a secondary stage, in what is known as the Teller-Ulam design. The first US test of a full scale device, Ivy Mike, took place in November 1952 at Enewetak Atoll with a yield of about 10.4 megatons. The largest weapon ever tested was the Soviet Tsar Bomba in 1961 with a yield of about 50 megatons.
Control and effects
Modern warheads are typically in the range of tens to hundreds of kilotons. Effects include blast, thermal radiation, prompt radiation and radioactive fallout. The Partial Test Ban Treaty of 1963 banned atmospheric tests and the Comprehensive Test Ban Treaty of 1996 has not entered into force. The world has roughly 12,000 nuclear warheads, with about 90 percent held by the United States and Russia, according to the Federation of American Scientists.
Based on data from the Federation of American Scientists and the US Department of Energy
