Fusion Bombs

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Thermonuclear, fusion (hydrogen bombs) explode with enormous power using uncontrolled self-sustaining chain fusion reactions. Deuterium and tritium, under extremely high temperatures, form helium providing the energy.

\[D + T \rightarrow ^4He + n\]

In principle, a mixture of D, T and ⁶Li heated to very high temperature and confined to a high density will start a chain fusion reaction, liberating an enormous amount of energy.

In a thermonuclear bomb, the explosive process begins with the detonation of what is called the primary stage. This consists of a relatively small quantity of conventional explosives, its detonation brings together enough fissionable uranium to create a fission chain reaction, which in turn produces another explosion and a temperature of several million degrees. When the temperature of the mixture reaches 10,000,000 K, fusion reactions take place. Fusion causes the temperature to rise, and neutrons released in fusion causes further fission of ²³⁸U, that releases more energy and radioactive fallout. In the design of thermonuclear bombs, the neutrons released in fusion are also used to generate more tritium by the reactions:

\[n + ^6Li \rightarrow T + ^4He\]

with cross section = 942 b

\[n + ^7Li \rightarrow T + ^4He + n\]

with cross section = 0.045 b

Fusion bombs can be thousands of times more powerful than fission bombs. However, since tritium, T, is a beta emitter with a half-life of 12.3 y. Therefore, fusion bombs requires a maintenance program.

Neutron Bombs

Fusion bombs designed to release neutrons rather than causing further fission reactions are called neutron bombs. Neutrons kill people, leaving the hardware and buildings intact.

The first thermonuclear bomb called Ivy Mike was tested on Enewetak atoll on Nov. 1, 1952, part of the Republic of Marshall Islands. After 2 minutes, the fire ball was 12 km (40,000 ft) high. After 10 minutes, the mushroom portion of the cloud was 16 km high and spread to a diameter of 160 km. The stem was 40 km high. More details are given in Power of the Ivy Mike Test. This is the 4th most powerful (10 megatons) test by the U.S. on Marshall Islands. The most powerful one on Feb. 28, 1954 Bravo Test with a yield of 15 megatons on the Bikini Atoll. U.S. Nuclear Tests in the Marshall Islands lists 67 nuclear tests from 1946 to 1958.

The mushroom cloud from the Mike shot

Contributors and Attributions

Chung (Peter) Chieh (Professor Emeritus, Chemistry @ University of Waterloo)