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Why can't X-Rays travel through water?

  1. Dec 3, 2014 #1
    I read that X-Rays cannot travel through water and I wanted to understand why. What happens when X-Rays and water molecules interact that prohibit X-rays from travelling within water?
  2. jcsd
  3. Dec 3, 2014 #2


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    http://www-als.lbl.gov/index.php/holding/167-isotope-and-temperature-effects-in-liquid-water-probed-by-soft-x-rays.html [Broken]
    Above describes interactions between x-rays and water. Water is not opaque to x-rays.
    Last edited by a moderator: May 7, 2017
  4. Dec 3, 2014 #3

    Vanadium 50

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    And you aren't going to tell us where, so we can't then look it up and find out what they are talking about?

    You are mostly water. If water were opaque to x-rays, you would be too. Does this sound right to you?
  5. Dec 3, 2014 #4
  6. Dec 3, 2014 #5
    Where do they mention x-rays in that paper? Can you indicate at least the page?
  7. Dec 3, 2014 #6


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    It's on the last page, left hand column, the paragraph immediately preceding "Noble Addition".
  8. Dec 4, 2014 #7


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    OK so they are referring to Soft X-rays not travelling through water which is basically correct

    medical X-rays are "Hard" X-rays ( higher frequency)


  9. Dec 4, 2014 #8
    Okee doke thank you for the clarification. But why cant soft xrays propagate through water?
  10. Dec 5, 2014 #9
    At reasonable* photon energies the main interaction between x-rays and matter is through the photoelectric effect: The photon gets absorbed by an atom and produces a free electron and a "hole" in the electronic configuration of the atom.

    The photoelectric cross section decreases very fast with the photon energy, i.e. low energy, soft x-rays are absorbed much stronger than high-energy, hard ones.

    In practice this means that x-rays with E<1keV cannot penetrate a sheet of paper whereas hard x-rays with E>50 keV can go through a lot of stuff - several centimeters of water, bones, even steel, rocks, etc.

    Visible light, IR and so on can travel through some materials if the photon energy is smaller than the band gap/smallest binding energy of the material. In that case the photons do not have enough "punch" to produce an electron-hole pair.


    * "unreasonable" according to this definition starts at a few 100 keV
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