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The graphs of radioactivity

  1. Jun 14, 2012 #1
    What would be the shape of an "Activity versus Number of Atoms present" graph look like... We know that A=-λN ... They are propotional but there is a negative sign.. What would be the graph?? Thanks in advance!
  2. jcsd
  3. Jun 14, 2012 #2


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    Activity is proportional to the number of atoms with a positive constant.
  4. Jun 14, 2012 #3


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    Maybe your book does it differently, but to me, activity is a positive quantity so A = λN. Over time, the number of undecayed atoms decreases at a rate that equals the (negative of the) activity, and this is where the minus sign comes in: dN/dt = -A = -λN.
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