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Homework Help: Sievert Calculations?

  1. Jun 3, 2015 #1
    1. The problem statement, all variables and given/known data
    So I'm looking at the radiation exposure risk regarding depleted uranium (U-238) and nuclear waste (4.20% U-235, 95.8% U-238).
    Yes I know these compositions are incorrect; they're close enough to exact for my purposes.
    The only information I have is the half lives of the uranium isotopes needed and the activity which I calculated myself in becquerels.
    Half lives
    U-235 703,800,000 years
    U-238 4,468,000,000 years
    2. Relevant equations
    Slightly relevant question: The half lives provided are values from Wikipedia because that's the only place I know I can get them from other than encyclopedia Britannica which posted different half lives (very different half lives; tens of millions of years different). Which source should I trust; or is there a better source for all my chemistry and physics needs?

    3. The attempt at a solution
    Activity of depleted uranium (DU)
    So using the formula:
    t = [ - ln ( 1 / 2 ) ] / activity in becquerels represented by lambda]
    substitute time in seconds from the half lives
    the "1/2" is the amount of atoms at a time over initial amount of atoms
    solve for lambda
    Answer is: 4.916 x 10^-18 Bq

    Now here's my problem; activity means nothing for my purposes. Activity as far as I know can't be converted to sieverts and I can't find anywhere telling me how to calculate sieverts. If I know the type of decay that U-238 undergoes when decaying can I calculate sieverts from that and activity?

    Any help would be muchly, greatly appreciatedly ;)
  2. jcsd
  3. Jun 3, 2015 #2


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    Homework Helper

    It seems what you are interested in is what is called the effective dose.
    It measures the amount of energy deposited by the radiation in one
    kilogram of a body, but it also takes the various types of radiation into
    account via a quality factor, QF. That is different QFs are assigned to
    the various types of radiation. The effective dose in sieverts, for a
    particular type of radiation is then

    effective dose (in sievert) = absorbed dose (in gray) x QF

    The absorbed dose depends not only on the strength and energy of the
    radiation but also on the material that is exposed to the radiation. That is
    bone will receive a higher dose than flesh.

    Why do you need these values?
  4. Jun 3, 2015 #3
    I'm writing a report on the feasibility of nuclear energy and one of the things I wanted to address is the issue of radiation exposure risk from waste when stored correctly and incorrectly; in water pools compared to say just left above ground.

    Thanks for the reply. I'll look into gray's in a few minutes
  5. Jun 3, 2015 #4
    So I had a look into this and found this equation:


    ca92d124392b614f90129615975eaf14.png is the mass-averaged absorbed dose of the entire item T
    b9ece18c950afbfa6b0fdbfa4ff731d3.png is the item of interest
    0f6accea29c9b0cd88f02c0bb8ad2f5c.png is the absorbed dose as a function of location
    92f53623b6d3e9d7fe7b56295ae69ffa.png is the density as a function of location
    5206560a306a2e085a437fd258eb57ce.png is volume

    Is it even possible for me to calculate the absorbed dose and subsequently the effective dose from the info I was given?
  6. Jun 4, 2015 #5


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    Homework Helper

    The formula looks sensible, but not helpful, yes.
    I don't know what data you have but the absorbed dose, that is the amount of energy that
    a kilogram of the exposed body absorbs from the radiation, depends on many factors like
    the strength (how much radioactive material is present) of the source S , how near or far
    the body B is from the source, the cross sectional area of the body, what types of radiation
    is present (the different types of radiation deposits different amounts of energy when it
    passes through the same material). Another complicating factor is that even the same type
    of radiation may have different energies, so you are getting into quite a lot of detail. Also not all
    of the energy of the radiation is absorbed when it passes through a body so one usually deal
    with a certain percentage that is absorbed. Maybe try and contact nuclear physicists at a
    nuclear power plant is an easy way out?
  7. Jun 4, 2015 #6
    Aha. Would you believe me if I said I already had. Contacted the World Nuclear association regarding a different question about a week ago but didn't speak to anyone "genius". The guy was more than helpful but his qualification was purely a bachelors of science so not much help there for anything more complex than the question I asked last time.

    Thanks for the info mate. I think I'll just forget about the sieverts and just use activity. It is a good enough measure for my purposes.
  8. Jun 4, 2015 #7


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    Homework Helper

    Here is a example problem in 5th ed Physics Giancoli P6040042.JPG P6040043.JPG P6040044.JPG
  9. Jun 4, 2015 #8
    Thanks for the reply. I've learnt something from this at least but I think I'll leave it out of my report; I believe this is above my knowledge and I don't want to dive into something and waste even more time than I already have on this assignment lol. Thanks again mate :)
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