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Homework Help: Nuclear Beta Decay (Parity, deta[L])

  1. May 31, 2010 #1
    I do not get the concepts of the parity change and how do I find the deta (l) for beta decay.
    Please Help!!

    Classify the following decays according to their degree of forbiddenness, all ground states decays.

    89Sr (5/2+) -> 89Y (1/2-)
    26Al (5+) -> 26Mg (2+)
    97Zr (1/2+) -> 97Nb (1/2-)

    What are theirs change in parity and deta (L)?
    How do you calculate it? Thanks again!
  2. jcsd
  3. Jun 1, 2010 #2
    Hey, I don't quite remember this but I'll try to explain how you do it for your first reaction.

    At the beginning, you can find the allowed values for L ( the orbital angular momentum ) via the angular momentum addition theorem: L = { |J1-J2|,..,|J1+J2|} in integer steps.

    As for the parity, for the 1st example you see that there is a change of parity: 5/2+ goes to 1/2-. This will have an effect on the allowed values of L. For parity to be conserved, you need to have:

    parity(Sr) = parity(Y)*parity(L).

    parity(L)= (-1)^L
    Hence you can see that only L=3 works here.
    While doing this, I have assumed a Fermi transition ( the electron & neutrino have opposite aligned spins ).

    If they for example they have parallel aligned spins, the transition will be Gamow-Teller and for the allowed values of L you will get only 2 ( you subtract 1 from all the values you got for the allowed values of L you got from the addition theorem ).

    So that's it I think. Your transition is 3rd forbidden pure Fermi.

    Now try for the next two examples and see if it matches with your school work.
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