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How do electrostatic feilds impact cloud chambers?

  1. Apr 16, 2012 #1
    Hello all,
    I just finished building an expansion cloud chamber this weekend and have started experimenting with it. Everything looks solid (vacuum, seal etc) but I'm curious about the role my electrostatic field, generated from a bug zapper and a circuit, plays in visualizing the ionizing radiation. I know it sweeps the air of charge. However, I'm not quite sure why it is so crucial to see the tracks my Americium 241 (taken from a smoke detector) produces through emission of alpha particles and the resulting ionization- I couldn't see anything without the electrostatic field. In short, I'm wondering specifically how an imposed neutral charge (electrostatic field) helps to see the tracks and how it can have such a profound influence on whether or not they are visualized.
    Thanks!
     
    Last edited: Apr 16, 2012
  2. jcsd
  3. Apr 16, 2012 #2
    The alpha particles produce a track of ionisation....+ and - charges as they pass through the air in the chamber. If you did not apply an electric field these + and - charges would recombine and tracks would be more difficult to see (if at all).
    The + or - charged ions produce strong nucleation sites for vapour to condense and produce droplets, ie tracks.
    The applied field separates the + and - ions
     
  4. Apr 18, 2012 #3

    sophiecentaur

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    So you are saying that the resulting ions will separate further from their electrons due to the E field and delay recombination? In my experience, you can still see tracks without needing any applied field.
    Is this because of the cloud chamber using expansion rather than ice and alcohol? Thogh I seem to remember being shown a demo when I was at School of an expansion cloud chamber in which you could see tracks without applying any E field.
    I wonder what's different.
     
  5. Apr 20, 2012 #4
    Yes, sophiecentaur, it's an expansion type cloud chamber, so creating a supersaturated environment relies on adiabatic expansion (achieved by pulling abruptly on a syringe) rather than dry ice. My diffusion cloud chamber, as you mentioned, can function without any electric field. Does anyone know, then, what prevents (or delays, at least) recombination in a diffusion cloud chamber?
     
    Last edited: Apr 20, 2012
  6. Apr 20, 2012 #5
    We have one expansion chamber and several diffusion chambers.
    The expansion chamber produces a general 'fog' of mist (alcohol) if the high voltage is not connected so no 'tracks' can be seen.
    The diffusion chambers are small plastic containers and the plastic top needs to be electrostatically charged by rubbing with a duster otherwise tracks cannot be seen.
     
  7. Apr 20, 2012 #6
    Interesting... the diffusion cloud chamber I built was actually made from glass and was quite large (I used a basketball case). I didn't charge it electrostatically at all, but it worked perfectly. I used this design:

    http://http://www.lns.cornell.edu/~adf4/cloud.html

    The instructions didn't call for creation of an electrostatic field, so I'm wondering if this is the type of cloud chamber you are referring to. Is the design of yours different?
     
  8. Apr 23, 2012 #7
    Hello everyone,
    I fired up the cloud chamber again and noticed that while my americium 241 produced a plethora of tracks from ionizing radiation, the beta source, strontium 90, produced none. Does anyone know if beta radiation can be visualized in an expansion cloud chamber?
     
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