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Homework Help: Ammount of plutonium left

  1. Sep 17, 2008 #1
    1. The problem statement, all variables and given/known data

    Plutonium 239 (P-239) decays at a rate of 0.00284 percent per year. If the initial sample size
    of P-239 is 10 g, how much will remain as P-239 after 20,000 years?

    2. Relevant equations

    A=A0e^-rt

    3. The attempt at a solution
    A=10e^-0.00284*20000
    lnA=ln10+lne^-56.4
    lnA=1-56.4
    A=8.7*10^-25
    This answer doesn't seem reasonable and I don't have confidence that I did everything correctly.
     
    Last edited: Sep 17, 2008
  2. jcsd
  3. Sep 17, 2008 #2
    I tried the question again.
    If A=A0*e^-rt
    I want to find A
    If I directly substitute and solve, I'll get..
    A=10e^(-.00284*20000)
    A=2.14*10^-24grams
     
  4. Sep 17, 2008 #3

    hage567

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    Homework Helper

    I think the problem is that you are putting 0.00284 in your equation. The 0.00284 is a percentage. So how else could you express that?
     
  5. Sep 17, 2008 #4
    Its a percentage so .00284 becomes .0000284?
    A=10*e^(-.0000284*20000)
    A=5.66grams
    That sounds more realistic. Is this correct?
     
  6. Sep 17, 2008 #5

    hage567

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    Homework Helper

    Seems reasonable to me.
     
  7. Sep 17, 2008 #6
    Thank you.
     
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