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25 July 2008

Answer to Question #1655 Submitted to "Ask the Experts"

Category: Radiation Basics — Fission, Fusion

The following question was answered by an expert in the appropriate field:

Fusion is based on joining two light nuclei together. The lightest element is hydrogen, and the two isotopes of hydrogen most readily fused together are hydrogen-2 (deuterium) and hydrogen-3 (tritium). Is this why fusion-based weapons are often refered to as hydrogen bombs?

Because of the short range of the nuclear force, nuclear reactions can occur only when two nuclei come into close proximity. In order for this to happen, one nucleus must approach another with sufficient energy to overcome the mutual electrostatic repulsive force of their like (positive) charges. It thus requires the least energy to bring nuclei with low atomic number together. It also happens that light nuclei can react by fusing, thus releasing energy. Naturally, the lightest element, hydrogen, has unique properties in this setting, which is exploited in the hydrogen bomb—a fusion weapon, as you state. The specific reactions involving the three isotopes of hydrogen in the weapon are described and shown in a table on p.508 of Dark Sun, the Making of the Hydrogen Bomb by Richard Rhodes (Simon and Schuster, New York, 1995). James Turner, CHP, PhD

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