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Lecture 9

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Author: Grant Mathews

Hydrogen Bomb - The fusion process

  1. 2H+3H --> 4He+n+Q = 17.6 MeV
    Energy release Q = 17.6 MeV (fission).
  2. In comparison:
    2H+2H --> 1H+3H +Q = 4.0 MeV
    2H+2H --> 3He+n +Q = 3.2 MeV
    3H+3H --> 4He+2n+Q = 11.3 MeV
    235U+n --> XA+XB+3n +Q  = 200 MeV (fusion).
  3. Fusionable Material
    1. Deuterium: natural occurrence (heavy water) (0.015%).
    2. Tritium: natural occurrence in atmosphere through cosmic ray
      bombardment; radioactive with half-life of 12.3 years.
  4. Two  “Advantages” of a hydrogen bomb
    1. Fusion is 4 times more powerful than fission
    2. Generates 24 times more neutrons.
  5. Fuel Considerations
    1.  Successful operation of a hydrogen bomb requires light, fusionable fuel
      1. deuterium for d+d based bombs
      2. tritium & deuterium for d+t based bombs
      3. tritium needs to be replaced regularly
      4. on-line produced tritium through lithium
    2. Industrial production facilities are necessary.
  6. Deuterium Fuel Production
    1. Deuterium separation takes place by electrolysis or chemical catalysts based methods with subsequent distillation.  Electrolysis separates water into oxygen and hydrogen. The hydrogen and  deuterium mix can then be liquefied and distilled to separate the two species.
    2. Chemistry-based methods include distillation of liquid hydrogen and various chemical exchange processes which exploit the differing affinities of deuterium and hydrogen for various compounds.  These include the ammonia-hydrogen system, which uses potassium amide as the catalyst, and the hydrogen sulfide-water system (Girdler Sulfide process). Process enriches deuterium to ~15%.  Distillation of deuterium-enriched water leads to 99% enrichment.
    3. Known producers are Argentina, Canada, India, Norway, plus all five declared Nuclear Powers, plus recent newcomers are Pakistan and Iran.
  7. Tritium fuel production
    1. Tritium occurs naturally, but in low abundance.  It can be made by accelerator or reactor based Tritium breeding through neutron capture.  The United States has not produced tritium since 1988, when the Department of Energy closed it’s production facility site in South Carolina. Immediate tritium needs are being met by recycling tritium from dismantled U.S. nuclear weapons.
  8. Disadvantages of a hydrogen bomb
    1. An acceleration of charged particles to energies above the Coulomb barrier is necessary.
    2. High ignition temperature (required: 50-100 Million K).

The Fathers of the (US) Hydrogen Bomb

 

All thermonuclear weapons existing in the world today appear to be based on a scheme usually called the "Teller-Ulam" design (after its inventors Stanislaw Ulan and Edward Teller), or "staged radiation implosion" for a physically descriptive designation.
  1. Teller, a Hungarian physicist immigrated to the US in 1935. Worked with Oppenheimer from 1943-1946 on the Manhattan Project.
  2. Ulam, a Polish mathematician. Came to the US (Harvard) in 1935.  Joined Manhattan project in 1943.

Lawrence Livermore Laboratory

 

The Lawrence Livermore Laboratory was founded in 1952 in the San Francisco Bay area as a second national weapons laboratory for the development and construction of the hydrogen bomb.  The first director was Edward Teller, a controversial figure, who fought with Oppenheimer about H-bomb feasibility, accusing Oppenheimer of disloyalty  (Oppenheimer lost his security clearance in 1954). Teller pushed weapons for the test program from the early 50s to the 80s and instigated President Reagan’s star wars program.

Ulam-Teller Design

 

Staged explosion of fission (primary) bomb and fusion (secondary bomb). The fission bomb is based on a regular Pu bomb design (Fat Man). Fusion device is based on d+d & d+t reaction with on-line Li-6 tritium production and neutron-induced fission.

Mike.jpg

XX-11 IVY MIKE, was fired on Enewetak by the United States on October 31, 1952. It was the first hydrogen bomb, an experimental device not appropriate for use as a weapon. This image is a work of a United States Department of Energy.

Mike (the first Hydrogen Bomb)

  1. The first staged fusion explosion (a bomb named "Mike") occurred on Eniwetok Atoll on Oct. 31, 1952.  Mike used liquid deuterium as a fuel.   The output of 10.4 megatons of TNT exceeded all of the explosives used in WW II, including both atomic bombs.
  2. The "Mike" device was essentially a very large cylindrical thermos flask for holding the cryogenic deuterium fusion fuel, with a regular fission bomb (the "primary") at one end; the latter was used to create the conditions for starting the fusion reaction.  The primary was a boosted fission bomb in a separate space atop the assembly.  The "secondary" fusion stage used liquid deuterium because this fuel simplified the experiment, and made the results easier to analyze. Running down the center of the flask which held it was a cylindrical rod of plutonium (the "sparkplug") to ignite the fusion reaction. Surrounding this assembly was a five-ton natural uranium "tamper." The interior of the tamper was lined with sheets of lead and polyethylene foam, which formed a radiation channel to conduct X-rays from the primary to secondary. The outermost layer was a steel casing 10-12 inches thick. The entire "Sausage" (as it was nicknamed) assembly measured 80 inches in diameter and 244 inches in height and weighed about 60 tons.  The entire Mike device (including cryogenic equipment) weighed 82 tons, and was housed in a large corrugated-aluminium building called a "shot cab" which was set up on the Pacific island of Elugelab, part of the Enewetak atoll.
  3. Mike consisted of a cylinder about 20 ft high,  ~7 ft wide, weighing 164,000 lb; The detonation of Mike left an underwater crater 6240 feet wide and 164 ft deep.  Mike created a fireball 3 miles wide; the 'mushroom' cloud rose to 57,000 ft in 90 seconds, and topped out in 5 minutes at 135,000 ft, with a stem eight miles across. The cloud eventually spread to 1000 miles wide, with a stem 30 miles across. 80 million tons of soil were lifted into the air by the blast.

Modern H-bomb design

The detonation of a trigger bomb will cause the following sequence of events:
  1. The fission bomb implodes, emitting X-rays.
  2. X-rays heat the interior of the bomb and the tamper; which prevents premature detonation of the fuel.
  3. The heat causes the tamper to expand and burn away, exerting pressure inward against the lithium deuterate. The lithium deuterate is squeezed by about 30-fold.
  4. The compression shock waves initiates fission in the plutonium rod.
  5. The fissioning rod gives off radiation, heat and neutrons.
  6. The neutrons enter the lithium deuterate, and generate tritium.
  7. The combination of high temperature and pressure is sufficient for tritium-deuterium and deuterium-deuterium fusion reactions to occur, producing more heat, radiation and neutrons.
  8. The neutrons from the fusion reactions induced fission in the uranium-238 pieces from the tamper and shield.
  9. Fission of the tamper and shield pieces produced even more radiation and heat.
  10. The bomb explodes.

Soviet Response 1955

RDS-37: The First Soviet Superbomb ("True H-Bomb") Test. November 22,1955; Semipalatinsk Test Site, Kazakhstan.

 

comparative nuclear fireball size.jpg

This graphic shows the comparative nuclear fireball diameters for a number of different tests and warheads. Image courtesy of Fasfission.

The Cold War and Nuclear Arms Race

  1. Each side built to ridiculous dimensions:
    1. Biggest US bomb: 1MT TNT MARK-17
    2. Biggest Soviet Bomb: 50 MT TNT Tsar Bomb
      The big bomb never had any military significance. It was a demonstration of force, part of the superpower game of mutually assured destruction. This was the main goal of the unprecedented test. Super-weapons are rejected by contemporary military doctrine, and the proposition that “now we have even more powerful warheads” is simply ridiculous.
  2. Attempts for stopping the race
    1. The Baruch Plan 1946; Bernard Baruch, U.S. representative to the U.N. Atomic Energy Commission, seemed to propose a radical plan to put atomic weapons under strict U.N. control. The United States was at the time the only nuclear power in the world. Under the so-called Baruch Plan, the United States would relinquish its atomic monopoly in favor of the creation of a new U.N. Atomic Development Authority, which would become the sole body in the world that could legally possess nuclear arms. Violators were subject to preemptive measures including a nuclear strike. The Soviet Union opposed the Baruch Plan, and in 1949 the first Soviet atomic bomb was detonated. 
    2. UN proposal for nuclear disarmament 1955; Soviet Union accepted the plan, after achieving hydrogen weapon success. In 1956 US rejected the U.N. proposed plan for disarmament and identified nuclear weapons as a “powerful deterrent to war”
    3. Unraveling of a Test Ban treaty
      1. The three nuclear powers refrained from testing beginning 1958. This voluntary "moratorium" was marked by several public statements of intent, by the United States, the United Kingdom, and the Soviet Union, in varying degrees of specificity and with various caveats.
      2. At the end of December 1959 President Eisenhower announced that the United States would no longer consider itself bound by the "voluntary moratorium" but would give advance notice if it decided to resume testing. The Soviet Government stated on August 28 and Premier Khrushchev repeated on December 30, 1959, that the Soviet Union would not resume testing if the Western powers did not.
      3. France conducted its first  test on February 13, 1960, two more later in the year, and a fourth on April  25, 1961. On May 15, 1961, the Soviet Government stated that if France continued testing, the Soviet Union might be compelled to test. On August 30, 1961, although neither the United States nor the United Kingdom had resumed testing and France had not continued to test, the Soviet Union announced that it would resume testing. It did so on September 1, thus ending the moratorium.  The United States resumed testing two weeks later.
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