thermonuclear weapon derives most of its explosive force from nuclear fusion.

• In a thermonuclear weapon, radiation from a fission explosion heats and compresses deuterium and tritium, which then undergo fusion.
• The fission component of a thermonuclear weapon is called the "primary." The fusion component is called the "secondary."
• Thermonuclear weapons are significantly more difficult to design, build, and maintain than fission weapons.

Thermonuclear weapons can be extremely powerful, with yields measured in megatons.

The largest nuclear weapon ever produced was the Tsar Bomba tested by the Soviet Union on October 31, 1961.

• The USSR claimed that the designed yield of the Tsar Bomba was 100 megatons, but the yield of the weapon was reduced to 50 megatons for safety reasons.
• Most U.S. experts conclude that the total yield of the weapon was about 57 megatons.

Go to: Chapter 2, page 4: Three Types of Nuclear Weapons