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What happens with the electrons in electrical appliances?

  1. Feb 21, 2016 #1
    Hi,

    I have a loose understanding of some things in life.
    This in particular regards the electrons in electrical appliances.

    Lets say electrons in a Geiger–Müller tube. They way it is described is that radiation interacts with the chamber wall or the gas and knocks out electrons. These electron causes electron avalanche because of the voltage placed on the anode, accelerations etc etc. The signal is the current produced from these charges. They describe it as the anode "collects" the electrons. The next signal can be produced as soon as the gas neutralizes, usually after some 100s mikroseconds.

    There is probably a lot of simplifications here. One question I have is, if the elctrons is collected at the anode, how is the gas in the chamber neutralized? Is there an influx of electrons from somewhere else compensating for the "collection" at the anode?

    Thank you very much
     
  2. jcsd
  3. Feb 21, 2016 #2

    davenn

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    Those electrons leave the anode, go through the circuitry, the power supply and back to the cathode of the tube

    1 electron out, another one in

    EDIT, I should clarify that a little
    A basic description ....
    There is a high voltage across the GM tube. but under normal conditions, the electrons on the cathode
    cannot traverse the path through the gas between the cathode and the anode.
    When a gamma ray passes through the tube, it ionises atoms of gas along its path.
    this allows the high voltage(energy) electrons to traverse that ionised path from the cathode to the anode

    NOTE: The gas is NOT a source for the electrons

    a fuller description ....
    https://en.wikipedia.org/wiki/Geiger–Müller_tube

    the GM tube I have is not one with a window on one end. It is a solid brass tube and as such will only detect X-rays and Gamma rays that can penetrate the thin brass tube. I cannot detect Alpha and Beta particles which are stopped very easily by many materials such as a sheet of paper etc


    Dave
     
    Last edited: Feb 21, 2016
  4. Feb 22, 2016 #3
    Thank you Dave for your quick reply.
    That makes sense.

    Another related question, in the same family, the Ionisation chamber, which also have an anode. The cathode in same cases does not seem so obvious. We have one where you can exchange the cap/chamber, and it looks like the only metal part is the anode. I think this also applies to most of the ionisation chambers, they have a plastic cap/chamber wall. I dont there is a metal coating on the inside.

    So, is it possible to only have an anode? That the voltage difference across the chamber is from the anode and to ground/chamber wall so, the previous reply that they are are returned to the cathode does not apply right?

    Thank you
     
  5. Feb 22, 2016 #4

    davenn

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    HI there

    I have never worked with ionisation chambers per-se so cant answer that directly.
    I will do some googling and see if I can find anything, you could do the same and see what either of us come up with
    some one else may also chime in

    it's possible the inner walls of the chamber ( if lined) are the opposite electrode

    Dave
     
  6. Feb 22, 2016 #5

    davenn

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  7. Feb 22, 2016 #6
    Thank you Dave.

    Yes, thats what they say. But I think there is something else to the story. I know for a fact that chamber walls for ionisation champer are often air or water equivalent to be able to measure a quantity that can be related to us humans (approx. water bodies).
    If I remember correctly according to the Bragg–Gray cavity theory, there should not be a metal in the field except for the anode. This would perturb the electron trajectories and the approximations made would not be possible.
     
  8. Feb 22, 2016 #7

    sophiecentaur

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    If you bombard an isolated piece of metal with ionising radiation (it only works for certain metals) you will cause electrons to be knocked off, leaving the metal with a positive charge. As you continue the bombardment, the metal will become so highly charged that it will attract the departing electrons and they will hang around in a cloud, with some of them constantly being attracted back. In the end there will be an equilibrium situation with the same number of electrons leaving as being recombined.
     
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