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Carbon-14 isotope question

  1. Mar 21, 2005 #1
    The half-life of carbon-14 is 5730 years. If a sample had 26 g of carbon-14, how much would it contain after 22,920 years (x 4)?
  2. jcsd
  3. Mar 21, 2005 #2
    calculate how many times the half-life time has past, you apparentely did so and that is 4 times, so that means that the original amount has halved 4 times...

    after 1 time the half-life time you have half of the original amount
    after 2 times the half-life time you have half of the half of the original amount so a quart
    after 3 times.......
  4. Mar 21, 2005 #3
    I did 26 divided by 4, does that work? Or do I keep halving it? As in 1.625?
  5. Mar 21, 2005 #4
    No if it halves 4 times, that does not mean yoiu have to divide by 4

    take for example 20 to start with,
    if you half that ones you have 10
    if you halve it a second time you have 5
    so after halving it two times you have what you had originally divided by 4

    you have to keep halving, four times.
    1/2 *1/2 *1/2 *1/2 = 1/16
    so you have to divide by 16
  6. Mar 21, 2005 #5


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    Homework Helper

    Since biology is a subdiscipline of physics, and since we are in the physics forum. Here is another way to look at your question.
    Radioactive decay of Carbon-14 follows an exponential decaying function of the form [tex] Ae^{-kt} [/tex]

    Carbon-14 follows the expontial decay: [tex] Q= Q_0 e^{-0.000121t} [/tex] :surprised
    where [tex] t [/tex] - years, [tex] Q_0 [/tex] - initial mass, [tex] Q [/tex] - final mass.

    So try that, plug in 26g for [tex] Q_0 [/tex] and 22,920 years for [tex] t [/tex],
    what do you get?

    Ask you teacher/professor: Knowing the half-life of Carbon-14, how can that be used to calculate the age of dinosaur bones or other organic matter? :uhh:
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