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Velocity of daughter nucleus

  1. Jun 3, 2007 #1
    1. The problem statement, all variables and given/known data
    1)Determine the maximum possible speed of the daughter nucleus in negative beta decay of a He(6,2) nucleus which is initially at rest.


    2. Relevant equations



    3. The attempt at a solution

    I solved in the following way:
    He(6,2) --> Li(6,3) + electron + antineutrino
    The daughter nucleus will have maximum speed when the electron and antineutrino has zero kinetic energy. Applying mass-energy equivalence,
    M(He)c^2 = M(Li)c^2 + K(Li)
    Where M(He)=atomic mass of helium isotope, M(Li)= atomic mass of Lithium isotope,
    K(Li)=Kinetic energy of daughter nucleus
    On simplification I get,
    K(Li)=3.52 MeV
    (1/2)M(Li)v^2=3.52 MeV
    On simplification I get,
    v=1x10^7 m/sec
    But the answer given in my book is 1x10^5 m/sec. Could someone please tell me where I have gone wrong?
     
  2. jcsd
  3. Jun 3, 2007 #2

    Dick

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    Your decay scenario doesn't conserve momentum! Use 4 vectors.
     
  4. Jun 3, 2007 #3

    malawi_glenn

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    The daughter nucleus will have maximum speed when the electron and antineutrino has zero kinetic energy.

    You must always consider momentum conservation!!
     
  5. Jun 3, 2007 #4

    Meir Achuz

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    Max daughter speed is when the e and antineutrino both go in the same direction. Then use E and p conservation.
     
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