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Recombination of ion pairs in an ionization chamber

  1. Oct 24, 2014 #1
    What happens to the fill gas in an ionization chamber?

    Once incident radiation has created an ion pair, which has then moved to its opposite polarity electrode, is that ion pair removed from the fill gas? So if enough incident radiation is detected over a period of time all the gas would be ionized and a vacuum left in its place?

    What then happens to the positive ion? Is it consumed in the same circuit the electron is? (The circuit that produces a representation of the incident radiation for the operator)

    If this isn't the case, when does the ion pair recombine whilst still giving an indication to the ionization chamber operator that radiation has been detected?
     
  2. jcsd
  3. Oct 24, 2014 #2

    mfb

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    Atoms don't magically disappear. The ion reaches the electrode, picks up an electron (this is part of the signal - you get electrons at one side and the other side needs additional electrons) and becomes an uncharged atom as part of the gas again.
    For noble gases, this is identical to the original state of the atom. For other gases, it means you break up molecules of an extremely tiny fraction of the gas. This does not matter - due to leakages, you need some constant gas flow through the detector anyway.
     
  4. Oct 24, 2014 #3
    Thanks mfb,

    So for an example using argon; once ionized the Ar+ moves to the negative electrode, is it at the surface of the electrode or 'inside' the electrode that it then recombines with an electron? Is it the same electron that is produced when the Ar is ionized, which it recombines with?
     
  5. Oct 24, 2014 #4

    mfb

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    It happens at the surface.
    Electrons are indistinguishable. And even if they would be distinguishable (to make an answer possible): No.
     
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