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Homework Help: Radioactiviy - # of unstable nuclei after 28 hours

  1. May 25, 2004 #1
    I'm having trouble working out how to calculate the number of unstable nuclei remaining in a sample after 28 hours, the answer is 10 but I have no idea how its done, any help would be greatly appreciated.

    "If a sample of radioactive material initially has 3.7 x 10(^7) unstable nuclei, how many would remain after 28 hours if the decay constant is 1.5 x 10(^-4)s(^-1)?"

    It suggested to use N = N_0 exp (^-decay constant x t) I converted the 28 hours to seconds giving me 100800, but I don't know what the "exp" is for or does.
  2. jcsd
  3. May 27, 2004 #2


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    Science Advisor

    How in the world did you get to a problem like this without having seen "exp" before? It is the "exponential" function: exp(x)= ex. If you are not familiar with that, you may find it on a calculator on the same key with its inverse, ln(x), the natural logarithm.
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