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Toxcicity of Plutonium and Bernard Cohen

  1. Feb 13, 2007 #1
    I recently read about Cohens challange to go on national tv against any nucler critic and eat as much Plutonium oxide in weight as the opponet eats caffeine.

    Ld50 for caffeine is around 13 grams. But if my calculations are right far less than 13grams of plutonium would be lethal. According to Cohen himself and other references the dose in Sv for each Bq of Pu239 ingested is 1*10^-7 Sv/Bq. 13grams of Pu239 is 3*10^10Bq so ingesting it should give a dose of 3000Sv!!!(Assuming it takes around 48hours for it to pass through the digestive system)

    So how could Cohen make that challange?:confused:
    Last edited: Feb 13, 2007
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  3. Feb 13, 2007 #2

    Andrew Mason

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    If he is serious he will eat it in a big lump and not grind it up and stir it into his coffee. I don't know where he is going to get 13 grams of Pu so I think he would have to break some laws to do this.

    As far as ingesting 13 grams of Pu239, that works out to 13/239 = .054 moles = 3.3x1022atoms. With a half life of 24000 years = 7.7x1011seconds, that works out to about 1010 disintegrations per second or becquerels. If it is in a lump, most of the alpha particles will be absorbed within the lump itself, so only gamma and beta particles will be a problem. I don't think that would kill anyone so long as it passed through in a normal time frame.

  4. Feb 13, 2007 #3


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    Your analysis is correct.

    Because of the short mean free path of the alphas emitted by the Plutonium; only the
    Plutonium that is on the surface has ANY chance of doing damage via alphas, which
    have the highest damage potential. The damage by alphas is about 20 times greater
    per unit dose than electrons or photons.

    That's the problem with the "zero-dimensional" analysis where one just computes the
    total radioactivity and compares to some Ld50.

    The vast majority of the ingested Plutonium is only going to irradiate itself.

    Professor Cohen is no dummy; he thought it out.

    Dr. Gregory Greenman
    Last edited: Feb 13, 2007
  5. Feb 13, 2007 #4
    It's 13 grams of PuO2, so taking into account the Oxygen, it's 13/(239 + 32) = 0.048 moles; that has an activity of about 26 GBq.

    If he does grind that up, then I'm getting the dose rate using

    D = AEavg [MeV / g * s] * 1.6E-13 [J / MeV] * 10E3 [g / kg]

    A is activity in Bq per gram
    Eavg is average energy of alpha particle

    The alpha particle for Pu decay is about 5 MeV and I'm guessing a stomach doesn't weigh more than 3 kg, so using that and the above equation, the dose rate comes out to 0.0069 Gy/s. About 25 Gy in one hour. :bugeye: Did I do that right?
  6. Feb 13, 2007 #5
    Ahh so that was what I was missing. I assumed he meant to ingest it as a fine powder, not acctualy swallowing a solid piece of it.
  7. Feb 16, 2007 #6
  8. Feb 17, 2007 #7


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  9. Feb 19, 2007 #8
    Yes the question was answered perfectly :approve: I even bothered to check out the range of 5Mev alpha particles in uranium(could not find it for plutonium but density is similar anyway) and its only and its only 8micrometer. So even thought the ball weights 10grams he would only get effected by a few micrograms on the surface.

    To bad no environmentalist has taken up Cohens challange.:grumpy:
  10. Apr 5, 2007 #9
    Chemical toxicity

    Plutonium is not only dangerous as a radiation source. It also has a chemical toxicity. It is a heavy metal that is likely to be absorbed by the bone surface, and there it can stay for years and release its radiation.

    It is the combination of radiation and chemical toxicity that makes Pu so poisonous.

    Ingestion of Pu is much less dangerous then ingestion of Po-210, because most of the Pu will be able to leave the body before it can decay (T1/2 for Pu = several years, while T1/2 for Po-210 = 138days)

    See: http://en.wikipedia.org/wiki/Plutonium#Toxicity
    Last edited: Apr 5, 2007
  11. Apr 7, 2007 #10

    Andrew Mason

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    It seems to me from this article that the actual toxicity of Pu to humans is not known.

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