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Carbon-14 Decay

  1. Dec 10, 2009 #1
    The radiocarbon in our bodies is one of the naturally occurring sources of radiation. Let's see how large a dose we receive. 14C decays via B- emission, and 18.0% of our body's mass is carbon.

    a) Write out the decay scheme of carbon-14 and show the end product. (A neutrino is also produced.)
    answer: 146C ------> e- + 147N + ve

    b) Neglecting the effects of the neutrino, how much kinetic energy (in MeV ) is released per decay? The atomic mass of C-14 is 14.003242 u.
    No idea where to begin tried using E = mc2 did not get the right answer.

    c) How many grams of carbon are there in a 76.0 kg person?
    no idea how to do this.

    d) How many decays per second does this carbon produce? (Hint: Assume activity of C-14 is about 0.255 Bq per gram of carbon.)
    No idea about this one either.

    Any help would be greatly appreciated.
  2. jcsd
  3. Dec 10, 2009 #2
    Carbon is 18.0% of body mass. 76.0 times 18.0%.

    Look up the definition of Bq (Becquerel) in Wikipedia.
  4. Dec 11, 2009 #3


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    It seems that it is a problem allowing you to use tables. Obviously to use E=mc2 (how do you pretend use it, anyway?) you need the mass difference between carbon and nitrogen. The data of the atomic mass of C-14 is in part a need and in part a red herring (so naive people will try to apply E=mc2 to it, instead asking the tables for the atomic mass of N-14 too).

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