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Radiocarbon dating

  1. May 7, 2015 #1
    1. The problem statement, all variables and given/known data
    9.2g of carbon got an activity of 1.6Bq, how old is it?

    2. Relevant equations
    A = -(lambda)*N
    N=No * e ^ -(lambda)*t
    (lambda) = ln2/t1/2

    3. The attempt at a solution
    The question dosnt specify which isotope of carbon it is so halflife remains unknown.
    I cant see how to solve this by only knowing the mass and activity.
    Could anyone give me pointers?

  2. jcsd
  3. May 7, 2015 #2


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    Homework Helper

    They are most likely referring to carbon-14 dating.
  4. May 7, 2015 #3
    Alright in that case we know the half life and can find the decay constant.
    Using A = -(lambda)*N we can find N as well (not sure If I need to divide the activity on 9.2g to get it per grams?)
    However It still leaves No and t unsolved.

    An alternative method is to; N=No * e ^ -(lambda)*t |*(lambda) => A=Ao * e ^ -(lambda)*t
    But it seems to get me to the same "deadend" where Ao and t is unsolved.
    I thought I might be able to set t=0 to get Ao but that only makes the expression " e ^ -(lambda)*t" equal 1.
    Any tips?


    PS: thanks for fast reply
  5. May 7, 2015 #4


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    Homework Helper

    Atoms per mole.
    The sample starts out with a certain fraction of it being carbon-14.
    Over time the amount of carbon-14 decays.
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