B41 Nuclear Bomb - Composition

Composition

The Mk 41 was the only three-stage thermonuclear weapon fielded by the U.S. It had a deuterium-tritium boosted primary, probably with lithium-6-enriched deuteride fuel for the fusion reaction in the secondary stage. This was followed by a yet-larger third fusion stage, the tertiary stage, compressed by the secondary stage. Finally, there was a fission jacket.

Two versions were deployed, Y1, a "dirty" version with a tertiary stage encased with U-238, and Y2, a "clean" version with a lead-encased tertiary. It was the highest-yield nuclear weapon ever deployed by the United States, with a maximum yield of 25 megatons (Mt), and weighing in at 4,850 kg. It remains the highest yield-to-weight ratio of any weapon created. The US claimed in 1963 that it could produce a 35 Mt fusion bomb, and put it on a Titan II (3,700 kg payload), almost doubling the yield-to-weight ratio of the B-41.

The Mk 41 was of the usual long cylindrical shape and weighed 10,670 lb (4,840 kg). The nuclear fusion warhead was of the Teller-Ulam type and used a 40–100 kiloton implosion type nuclear fission primary fueled by HEU to trigger the lithium-6 deuteride fusion fuel. Between 500 and 1,000 kg of lithium deuteride was used and was contained in a cylinder of natural uranium with an inner casing of U-235.

The Mk 41 was an example of a fission-fusion-fusion-fission type thermonuclear weapon, or tertiary stage bomb. The additional tertiary fusion stage, compressed by a previous fusion stage, could be used to make a bomb with yields as large as desired (see Tsar Bomba, a Soviet three-stage bomb and the highest-yield nuclear weapon ever built or tested).