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Decay of Cr

  1. Jun 4, 2008 #1
    One more question (I'm wary I'm totally spamming the forum!).. its in reference to the decay of Cr to V, see attached files.

    The decay is clearly beta plus decay.


    The question asks to determine the neutrino spectrum. Now the energy of the neutrino is simply the mass difference between the {original state} and {the GS of the final state PLUS the rest mass energy of a positron}.

    Why on earth is the question talking about a K shell electron? I also attach the solution to the problem. It doesn't take into account mass of the positron when calculating the energy of the neutrino: Why?

    Attached Files:

  2. jcsd
  3. Jun 4, 2008 #2

    Vanadium 50

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    Since it's a homework problem, I'll only give you a hint.

    Hint: What positron?

    Second hint: reread some of the other threads you've started.
  4. Jun 4, 2008 #3
    well you said in the other thread that the positron is very short lived (I take it undergoes electron positron anhiliation?).

    Therefore I would think this energy radiates away to the surroundings - ie. it is not captured by the neutrino...

    I don't really get it to be honest:(

    EDIT: ALSO according to the solutions (the second file), the K shell energy of the original particle has been subtracted from the difference in masses. Why is a K shell electron liberated in this decay... a positron should be produced, not an electron liberated.
    Last edited: Jun 4, 2008
  5. Jun 4, 2008 #4

    Vanadium 50

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    Let me give you the hint again. What positron? Point to the positron in the diagram.

    If you need another hint, look up the decay modes of Cr-51.
  6. Jun 4, 2008 #5


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    No, it isn't. Look at the NNDC website if needed (the chart of nuclides).
  7. Jun 5, 2008 #6
    aaah I see, its K shell capture.

    So V captures a K shell electron. Another stupid question, why is it K shell capture? V already has a (two) K shell electron(s); do you not need an x ray photon to knock of one of these in the first place? It would seem a lot easier for the electron to tag onto on of the valence shells, no?
    Last edited: Jun 5, 2008
  8. Jun 5, 2008 #7


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    Cr captures K-electron and a proton is transformed to a neutron (A remains unchanged, but Z decreases by 1).

    All elements from He on have 2 K-electrons, and they are most tightly bound to the atom/nucleus. QM-wise, K electrons have a greater probability of interacting with the nucleus. An ionizing X-ray would be one that 'lifts' the electron up out of the potential well.
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