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Homework Help: Radioactive Decay?

  1. Nov 8, 2012 #1
    1. The problem statement, all variables and given/known data

    A meteor contains 2.45kg of plutonium-239. It has a half-life of 24065 years. Calculate:
    a) The number of plutonium molecules currently present in the meteor (at. mass = 239.052)
    b) How long ago the meteor struck the earth if originally it contained 10kg of plutonium.

    2. Relevant equations
    no.atoms= mass/(atomic mass) x avagadro^' s no.(6.02x〖10〗^23)

    N = No e-γt
    where the decay constant, γ(gamma), and T1/2 are related by
    γT1/2 = ln(2)

    3. The attempt at a solution
    I solved A, and achieved an answer of 6.16979x1024 particles.
    I'm confused as to where to go from here.
  2. jcsd
  3. Nov 8, 2012 #2
    just obtain a value for γ, substitute it into N = No e^(-γt) and solve for t
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