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Fizzle Material

  1. Mar 1, 2009 #1
    Hey all,
    I had a somewhat technical question concerning recent news events. My background in physics and mathematics is limited, especially in the area of atomic energy and science. Recent news reports have stated that Tehran now has 1,010 kilogrammes of low-enriched uranium hexafluoride, which, according to the department of Defense, is enough uranium to make a bomb, assuming it was adequately enriched. So my question is, enough this enough to engineer a bomb? What other factors are required? What is "fizzle" material?
  2. jcsd
  3. Mar 1, 2009 #2


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    Well, the term is fissile, and the exact amount depends on the level or enrichment/purity of the fissile isotopes U-235 or Pu-239.

    Weapons grade U-235 typically means greater than 70% U-235 in U. The lower the enrichment, the greater the amount of U required, but also the yield is lower than U or greater U-235 content.

    If low enrichment means 5%, the 1000 kg of U would have 50 kgs of U-235, which is about enough for one device if the final composition is close to pure. If it's UF6, it depends on the enrichment of U-235 which would likely have to be greater than 5%.
  4. Mar 2, 2009 #3
    Tehran has 1010 kg of uranium hexafluoride enriched to 3.5%. If they were to continue enrichment and to extract all U-235, they would end up with approximately 20 kg of pure metal.

    Critical mass of a bare sphere of U-235 is 50 kg (higher if it's impure). Through the use of implosion techniques and neutron reflectors, it is theoretically possible to build a working bomb with less, supposedly with as little as 15 kg.

    To get to the point where they can build a bomb, they would have to enrich their existing uranium to 70% or higher. It is not something that can be done overnight or right under IAEA's noses. It would take considerable time (many months) to enrich all their existing uranium to weapons grade. And it's very hard to justify enrichment beyond 20% or so for peaceful purposes. They would have to kick out IAEA inspectors first, at which point Israel would surely bomb their nuclear program into the stone age.

    If they are indeed interested in making bombs, they would have to build up some sort of secret facility and gradually funnel off low-enriched uranium into that facility.
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