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B No traces in cloud chamber (experimental physics)

  1. Sep 20, 2016 #1
    My setup:
    • plastic box (~1l) with the cover painted black mat
    • the bottom of the box covered with sponges saturated with ethyl alcohol (90%) to the limit (all over sponge capacity poured back to bottle)
    • turned upside down and placed on ~0.5kg of dry ice.
    I can see a 'rain' of particles of alcohol, but no traces.

    I disassembled smoke detector and attached the sample of americium to the box. No effect.

    Here is the 'rain':

    Here are some pictures of the setup:
  2. jcsd
  3. Sep 20, 2016 #2


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  4. Sep 20, 2016 #3

    Stephen Tashi

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    Was it 90% or "90 proof" ?
  5. Sep 21, 2016 #4


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    I've never made one of these (must try sometime), just wonder whether you'd do better to have the light in a different position? Either sideways, or preferably pointed away from the viewer, so that you see only back scattered light. I can see you might have a problem with reflections off the walls of the box, but maybe light entering the side wall aimed (say 30-60o) at the back wall would reflect to the other sidewall, leaving the viewer with no direct light.

    This may not explain your lack of traces though, because your eye would probably discriminate much better than the camera and pick out the tracks even against the light.
  6. Oct 16, 2016 #5
    Plastic may be the issue.
    Do you have a metal lid? if not then the plastic box is 'Insulating' your setup. you need to maximise your conductivity thereby increasing your steep temperature gradient. your environment probably isn't supersaturated enough, and I might add, try using methanol, or I.P.A, its usually 99% proof and this does contribute to saturate the chamber environment better.

    Good Luck
  7. Oct 17, 2016 #6
    There are several problems in the installation above. One is that the box is actually not sealed. It would be better to not let exchange gases with the warm air of the room. The second is the box material, as Simon pointed out. The conductivity of plastic makes it long before the vapors inside cool enough. A jar with metal cover is much better.
    And last, but not least, the light, as Merlin wrote above should be partially covered to make stronger contrast between the observable area and the rest, witch should be in dark.

    Another suspicious was that the 'snow' I am observing are particles of alcohol, that already condensed (that's why they are so visible), but we saw traces in the 'snow', so there are still saturated alcohol that wants to condense.

    I am still before getting good enough results, but the next attempts wait for better preparation of the experiment.

    Thank you all for the advises.
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