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Homework Help: Radioactivity and radioactive decay, again sorry

  1. May 7, 2008 #1
    1. The problem statement, all variables and given/known data
    Thorium (with half-life T1/2 = 1.913 yr. and atomic mass 228.028715 u) undergoes alpha decay and produces radium (atomic mass 224.020186 u) as a daughter nucleus. (Assume the alpha particle has atomic mass 4.002603 u.)

    The energy released from the decay of 0.6 g of thorium is used to heat 3.5 kg of water (assume all the energy released goes into the water).

    (c) What is the change in temperature of the water after 2.6 hrs.?

    2. Relevant equations

    Th --> Ra + He
    [tex]\Delta[/tex]m= M(Th)-M(Ra)-M(He)

    3. The attempt at a solution
    [tex]\Delta[/tex]m= .005926 u
    So, I can find the energy, but in the "help," it says to find the number of atoms. How do I find the number of atoms?
  2. jcsd
  3. May 7, 2008 #2
    You know the atomic mass of Thorium - and you also know 1 atomic mass unit = 1.66053886 × 10-27 kilograms. You also know you have 0.6 g of Thorium -

    N_o = total mass/ mass per particle.
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