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Is charge conserved in positron emission?

  1. Mar 13, 2012 #1
    Consider the reaction:

    [itex] ^{39}_{20}Ca \rightarrow ^{39}_{19}K + \beta^{+} [/itex]

    I understand that a proton in the Calcium nucleus is being split into a neutron, which stays in the nucleus, and a positron, which gets ejected.

    But if you look at the equation above, charge is not conserved. The only thing I can think of doing to balance is to consider the potassium product as a negative ion, but that makes no sense to me?

    Or perhaps I am missing something. Or perhaps it has something to do with the number of electrons in play.

    Any help is appreciated. Thanks!

  2. jcsd
  3. Mar 14, 2012 #2


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    Staff: Mentor

    Charge is conserved always. Equation is just not complete, but when writing nuclear reaction we don't pay much attention to such things, we concentrate on what is important from the point of view of the nucleus (this is not a chemical reaction). Once the positron is emitted you end with an excess electron in the atom shells. Later this electron will look for a better place for itself, which usually means traveling to some other atom/ion whatever.
  4. Mar 14, 2012 #3
    I see! Thanks Borek!
    So techniclly, the potassium is actually an anion but we don't really care about that charge in nuclear reactions since the electron will quickly move somewhere else right?

  5. Mar 14, 2012 #4


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    Staff: Mentor

    More or less.

    Depending on the nuclear reaction it may happen that nucleus (or several) lands in a different place it originally was (think fission). They move independently from the electrons generating a mess on their way (there is a reason why we call some forms of radiation ionizing).
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