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Why does Z=-1 for a beta minus particle?

  1. Nov 9, 2008 #1
    This sounds like a silly question but if

    Z (atomic number) is defined as the number of protons in a nucleus.

    Why does Z=-1 for a beta minus particle? (since it is just an electron)

    I know what is happening with the decay that a up quark turns into a down quark so that a neutron turns into a proton, electron and electron neutrino but I see no reason other than saying the atomic number must be conserved in the decay equation for Z=-1 for the beta particle.

    It seems to me that we have decided that Z=-1 to fit a rule for conservation of atomic number and for no other reason.

    I know that there must be an error in my thinking somewhere but where?
  2. jcsd
  3. Nov 9, 2008 #2


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    Homework Helper

    You can also define Z as the number of positive charged entities within a nucleus. Hence when the nucleus are gaining one positive charged entity (neutron -> proton ) one negative charge must "fly away" (electron + neutrino). So it depends on how you define Z.. it's not a big deal - the most important thing is that you understand the physics and that what is important is electric charge conservation.

    There are many funny and strange notations in physics, many are historical.
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