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Homework Help: Radioactive decay and power

  1. Feb 7, 2009 #1
    1. The problem statement, all variables and given/known data
    Plutonium-238 with a half-life of 90 years, emits and alpha particle of energy 5.10 MeV. 180mg of this radioisotope is used to power a pacemaker. Calculate the initial power in mW, supplied by Plutonium-238, assuming a 100% efficiency for the conversion of decay energy into usable power.

    2. Relevant equations
    I tried using:
    N = No(1/2)^(t/T), where T is the half-life
    P = W/t

    3. The attempt at a solution
    I do not know what "time" to use in order to calculate the power. What does it mean by "initial"?
    Help would be very appreciated.
  2. jcsd
  3. Feb 7, 2009 #2


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    Initial means assuming that none of it has decayed yet
    Watts are joules/second so you need to work out how many decays in the first second
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