B41 (nuclear weapon)

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View of a B41 hydrogen bomb

The B41 or MK 41 was a thermonuclear bomb that was in the arsenal of the US Strategic Air Command from 1960 to 1976. This bomb was the most powerful nuclear weapon developed by the United States. Their explosive power was given as “less than 10” or 25 Mt TNT .

development

Test Hardtack I "Poplar", clean two-stage version of the TX-41 draft

The development of the B41 began in 1955 when the USAF formulated the demand for a new class B (about 10,000 lb, about 4.5 t) nuclear weapon with high explosive power. The UCRL (University of California Radiation Laboratory, now Lawrence Livermore National Laboratory LLNL) proposed adapting an experimental three-stage Teller-Ulam design that was currently under development in that laboratory. This design was first tested during Operation Redwing in the Zuni test on May 27, 1956. The experimental explosive device was named "Bassoon". This was the world's first test of a three-stage nuclear weapon with a Teller-Ulam design and one of the "cleanest" tests in US history, as only about 15% of the explosive force of 3.5 Mt was generated by nuclear fission . Less than two months later, “Bassoon Prime” was tested, a “dirty” version of the three-stage design, in which the third stage was encased in depleted uranium rather than lead as before. In this test on July 20, 1961, called Tewa, an explosive force of 5 Mt was achieved, 87% of which was generated from nuclear fission. Measured by its explosive power, Tewa was the “dirtiest” test in US history. These two tests of the Redwing series were only intended to provide proof in principle that the concept works and were not yet tests of the actual bomb design.

In November 1956 the feasibility study for the new weapon was completed and the designations TX-41 for the bomb and XW-41 for the missile warhead were given. On January 28, 1957, the US Department of Defense officially commissioned the US Atomic Energy Commission (AEC ) to develop the new weapon based on the UCRL draft. The following January the military characteristics of the bomb and missile warhead were approved and the drafting and design phase began. In July 1957, the missile warhead was canceled.

On August 31, 1957, the first stage ("primary") and second stage of the TX-41 were tested in a mock-up of the later bomb in the test "Smoky" of Operation Plumbbob . The achieved explosive force was 45 kt, only a small part of it by nuclear fusion. There were three tests on the TX-41 design during Operation Hardtack I. The first test, "Sycamore", failed. He should test the "clean" version of the TX-41 draft. Instead of the predicted 4 to 6 Mt, it only achieved an explosive force of 92 kt with only a very small proportion of nuclear fusion in the second stage. The clean two-stage version was tested again in the "Poplar" test and developed 9.3 Mt of explosive power. This was the fifth largest nuclear explosion in US history. A “clean” three-stage version was tested in the “Pine” test and achieved 2 Mt explosive force, only about half as much as predicted.

Production of the first engineering models of the TX-41 then began in 1958, with serial production of the bomb now known as the B-41 commenced in September 1960.

Test date Proving Ground Test series Test name Explosive device name calculated explosive force achieved explosive power Details
May 28, 1956 Bikini Atoll Redwing Zuni Bassoon 2 - 3Mt 3.5 Mt Test of a three-stage "clean" Teller-Ulam design, first test of a UCRL draft, first test worldwide of a three-stage Teller-Ulam design, basis for the TX-41 design
July 20, 1956 bikini Redwing Tewa Bassoon Prime 6 - 8 months 5 months Test of a "dirty" three-step design, basis for the TX-41 design
August 31, 1957 Nevada Test Site Plumb bob Smoky n / a 45 - 50 kt 44 kt Testing the primary stage and the second stage of the TX-41 draft
May 31, 1958 bikini Hardtack I. Sycamore n / a 5 months 0.092 Mt Test of the "clean" two-stage TX-41 design, failure
July 12, 1958 bikini Hardtack I. Poplar n / a 5 - 10 months 9.3 Mt Repeat test for failed Sycamore test
July 26, 1958 Eniwetok Hardtack I. Pine n / a 4 - 6 months 2 months Test of the "clean" three-stage design of the TX-41

construction

The B41 was the only US thermonuclear weapon that operated on a three-stage Teller-Ulam design . A nuclear fission explosive device ("primary") ignites a second stage based on nuclear fusion ("secondary"). The energy released in the second stage is used to ignite a third stage, which is also based on nuclear fusion. The first stage was based on the implosion process and was boosted by the deuterium and tritium gas inside . The second stage is a cylinder that is filled with enriched 6 LiD and encased in lead. The third stage has a similar structure to the second, but it was probably made in two versions: For the B-41-Y1 bomb, the third stage was encased with depleted uranium. The rapid nuclear fission of the uranium increased the weapon’s explosive power considerably. This weapon works according to the design Fission-Fusion-Fusion-Fission (FFFF). In the B-41 Y2 version, the third stage was probably coated with lead like the second. As a result, it has less explosive power, but also produces significantly less radioactive fallout . The Y1 version probably has an explosive force of 25 Mt, the Y2 version less than 10 Mt. The B-41 Y1 is close to the theoretical maximum for the ratio of explosive force to bomb weight for nuclear weapons. The weapon put into service had a ratio of 5.2 kt explosive force per kg bomb weight. The pure explosive device without a parachute and shock absorber of the bomb housing is considerably lighter, however, and thus the B-41 reached the limit of 6 kt / kg specified by Theodore B. Taylor .

Dimensions

  • Length: 3.76 m (12 ft 4 in)
  • Diameter: 1.32 m (4 ft 4 in)
  • Mass: 4,850 kg (10,670 lb)

The weapon was intended for the B-52 or B-47 bombers. It could be detonated on a parachute in the air or on impact on the ground.

Commissioning

The B41 entered service as the MK 41 in 1961 and as the B41 from 1968. About 500 units were built between September 1960 and June 1962. From 1963 the bombs were gradually decommissioned. The last B41s were decommissioned in 1976.

credentials

  1. a b c d e [The Nuclear Weapon Archive - The B-41 Bomb]
  2. ^ Nuclear Weapon Archive - Operation Redwing
  3. ^ Nuclear Weapon Archive - Operation Plumbbob