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Will 2.8 micro curie of radiation cause cancer

  1. Aug 17, 2012 #1
    I have been working with a 2.8 (decayed over summer) micro curie cobalt-57 source testing a gamma camera. I would like to know if this made my risk for getting cancer higher ? My employers say l don't need to be worried.
     
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  3. Aug 17, 2012 #2

    bcrowell

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    There is no way to answer this question without knowing your dose. You presumably are wearing a dosimetry badge, and you should be getting monthly reports of your integrated dose. Unless you give us this number, we can't tell you anything useful. If this 2.8 uCi source has been in your pocket 24 hours a day for 3 months, that's one dose. If you've been working a meter away from it for a few hours a day for 3 months, that's a whole different dose.

    Let's assume that your dose for this summer has been less than 1000 uSv. In that case, we may be able to answer two logically distinct questions: (1) has it made your cancer risk higher? (2) if so, then how much increased risk have you experienced?

    Nobody knows the answer to #1. There is a variety of evidence that there is a general effect called radiation hormesis, in which an organism's health *improves* due to exposure to small doses of radiation. We don't know if this effect applies to humans, because we can't do controlled experiments with humans. If it does, then the answer to #1 is no. Your risk has not increased, it has decreased.

    The answer to #2 is that any increase or decrease is too small to worry about. It is much less than the incremental risk you would get by living in Colorado for a year.

    The more general question is what methods you're using to judge the reliability of your sources of information. Why should you trust me, a random person on the internet, more or less than your employer? This is an issue on which many otherwise intelligent people have amazingly stupid ill-informed opinions, and if you ask enough of them, they will be happy to share those opinions with you.
     
    Last edited: Aug 17, 2012
  4. Aug 18, 2012 #3

    mfb

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    I can give you an upper limit: Co-57 decays with 0.8 MeV to (stable) Fe-57. If the source was in your pocket all the time for 3 months, and your body covered 50% of the solid angle, and it was radiating at 2.8µC all the time, the total energy you received was 52mJ. Distributed over ~80kg and with a weighting factor of 1 (gamma rays), this corresponds to ~0.63 mSv. Similar to the natural radiation your receive within 3 months.

    With 40 hours per week instead of 24/7, this is reduced to 0.15mSv.
    If the source had some distance to you, the number gets reduced again. In addition, not every photon will interact in your body - some of them just fly through. And maybe there was some shielding involved?

    And this is right. While I would not recommend it, even eating that source (worst thing you can do) would not give a radiation level significant above the natural irradiation.
     
  5. Aug 18, 2012 #4

    bcrowell

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    Mfb, my only quibble with your calculations is that you're calculating a whole-body dose. If the OP keeps it in a pocket, for example, then a certain spot on his/her thigh will get a much higher dose. (In this situation, the dosimetry badge also will not tell him/her anything useful.)
     
  6. Aug 18, 2012 #5

    jtbell

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    The intensity of the radiation drops off as 1/r^2, so it makes a big difference (at least in the numbers) between having one of these sources next to your skin versus a few feet away. I've always told students that I wouldn't carry microcurie sources around in my pocket continuously for weeks on end, but otherwise they're safe for normal handling and use in a lab situation.
     
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