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Homework Help: Recoil speed of an atomic nucleus

  1. Nov 15, 2009 #1
    1. The problem statement, all variables and given/known data

    An atomic nucleus is in an excited state. It decays to its ground state with the emission of a gamma ray having energy, Egamma = 24.0 keV. The nucleus has a mass of 9.53e-26 kg. What is the recoil speed of the nucleus? (Note: This may be an inelastic collision)

    2. Relevant equations
    1 eV = 1.6e-19 J

    3. The attempt at a solution
    I tried setting the final kinetic equal to the rest energy, and I tried setting it equal to the energy of the gamma ray, and I can't get the answer. The answer key lists the correct answer as 134 m/s, and I have no idea how to get to that.
  2. jcsd
  3. Nov 15, 2009 #2


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    Homework Helper

    Why not use conservation of momentum?
    Use the special formula for the momentum of a photon, using its energy to calculate its momentum.
  4. Nov 16, 2009 #3
    Thank you, I got it now :)
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