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Ionizing Radiation in a Cloud Chamber

  1. Mar 23, 2013 #1

    I've been doing a lot of research on cloud chambers recently, and I've
    come up with a quite a few questions on the behavior of certain types
    of ionizing radiation:

    1) For a start, I assume that gamma-rays and X-rays will induce Compton
    scattering inside the cloud chamber. Would a photon realistically undergo
    the compton effect multiple times?

    My guess: Yes. However, after a few times, the photon will no longer possess
    enough energy to undergo the compton effect.

    2) I know the compton scattering equation:

    λ' - λ = (h/mc) (1 - cosθ)

    Unfortunately, I can only realistically approximate the value for λ, while I have
    no way to find the value of θ or λ' based on the trails in the cloud chamber. Is
    there any way I could figure out or at least estimate such values?

    3) The trails caused by beta decay in the cloud chamber bend much less than electrons
    created through compton scattering by gamma rays. Is there any scientific reason
    for this phenomena?

    I'm assuming that my "compton scattering assumption" is accurate. If it isn't I would
    appreciate if a better explanation could be provided.

    I'm not sure if this should have gone in the homework section. If it should
    have, sorry in advance!

    Thanks for the help!
  2. jcsd
  3. Mar 24, 2013 #2


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    If the energy is high enough, sure. Pair production is possible, too, if the energy is high enough.

    Ýou will need the electron energy, the direction of the photon source or the direction of the photon afterwards, I think.

    Less energy for Compton photons. That depends on the energies of your photons and beta decays.
  4. Mar 24, 2013 #3

    2) So it is unlikely that I will be able to mathematically analyze
    what happens in a cloud chamber, since I cannot measure
    the angle with which an electron shoots out in a cloud chamber.

    3) Is it valid to say that when a free electron interacts with an
    atom, the coulumbic forces between the two particles could
    knock out an electron and bend the incoming electron (provided
    it as enough energy)?

    Note: THe gamma source I am analyzing is uranium ore. I am
    comparing the electron trails from compton scattering to
    the beta trails emitted by the uranium ore.

    Thanks for the help!
    Last edited: Mar 24, 2013
  5. Mar 24, 2013 #4


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    Anything would work, including the energy of the electron (curvature in a magnetic field?).
    That is a possible process, indeed.
  6. Mar 24, 2013 #5

    So higher energy beta particles, that have more kinetic energy
    and momentum are able to retain their original path better than
    lower energy particles, which can be more easily bent by a force.

    So why do some high energy beta particles not ionize at all. Would
    it be due to a smaller timeframe between which the coulombic forces
    between the two electrons interact?
  7. Mar 24, 2013 #6


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    Which particles do you mean?

    The ionization rate drops with increasing velocity (and slowly rises again for very high energy), but it does not go to zero.
  8. Mar 24, 2013 #7

    Oh, that seems to make more intuitive sense.

    In the cloud chamber, high energy beta particles didn't
    create any trails, so I assumed that they were not
    ionizing the vapor.

    I suppose it simply didn't ionize enough particles to create
    noticable trails. Another question that pops up:

    Why would the electrons have a somewhat low energy? Is
    there a scientific explanation for this phenomena?
    Last edited: Mar 24, 2013
  9. Mar 24, 2013 #8


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    How did you know they were there?
    Which electrons?
    Compton electrons have a broad distribution of energy, as you can calculate with the help of the formula in the first post.
  10. Mar 24, 2013 #9

    That is a good point......:rofl:

    The beta source was certainly radioactive though -
    the geiger counter registered a large amount of radiation
    from it. I have heard of cases where a substance is so
    radioactive, the cloud chamber ceases to work well (I have
    no idea why).

    Sorry for the vague questions, but the electrons I was
    talking about were those that were compton scattered in
    the cloud chamber. It my cloud chamber, the electrons
    that were scattered tended to bend easily, so I assumed
    they had lower energy than beta particles (which did not
    bend easily).

    I was wondering if there was any reason that the electrons
    tended to have lower energies. Lots of the electrons were
    bending, so it didn't seem like it was completely randomized
    (although it seems like it should be).
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