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Can you classify ordinary light as ionizing radiation?

  1. Jul 4, 2014 #1
    Can you classify ordinary light as ionizing radiation?

    Okay. So, I'm thinking that ordinary light has about 2 eV of energy per photon.
    But, alpha, beta and gamma ray have huge eV from 0.1 to 10 MeV.

    However, could there be a case where the 2 eV could knock out an electron and cause ionization?
     
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  3. Jul 4, 2014 #2

    mfb

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    There are some materials where 2 eV is enough to free an electron, but that does not count as ionizing radiation. Chances are good that such a weakly bound electron was not relevant for the chemical stability of the material anyway.
     
  4. Jul 4, 2014 #3
    Ok. If we fire a bright spotlight to atoms, can't several photons consecutively hit the same electrons and make them go out?

    Sorry if it seems dumb.
     
  5. Jul 4, 2014 #4

    SteamKing

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    The short answer is no.

    Read the first paragraph of this article:

    http://en.wikipedia.org/wiki/Ionizing_radiation
     
  6. Jul 4, 2014 #5
    @SteamKing, would you give the long answer? It's really grudging that I must satiate myself with that first paragraph :(
     
  7. Jul 4, 2014 #6

    SteamKing

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    When you see a sentence like, "...whereas the lower ultraviolet, visible light (including laser light), infrared, microwaves, and radio waves are considered non-ionizing radiation." the use of the verb 'considered' often means that a convention has been adopted or a judgment call made.

    In this case, although there are certain conditions under which visible light can cause an electron to be stripped from an atom, just like what would happen if a gamma ray or an x-ray did, the judgment is that the ionizing effect of exposure to visible light is nowhere near as hazardous as uncontrolled exposure to x-rays or gamma rays, which can be downright lethal.

    Visible light is naturally present due to the sun, whereas x-rays and gamma rays, which are also produced by the sun, are not normally present in large amounts on the earth's surface due to the protective effects of the atmosphere. Exposure to non-lethal amounts of x-rays or gamma rays can lead to damage to one's DNA and assorted mutations, where this is not the case with exposure to visible light. [The tanning of the skin is the body's protective response to exposure to UV rays produced by the sun, and naturally, there are warnings against overexposure to UV light (even from tanning beds) and suggestions to liberally apply sunscreen when outdoors for lengthy periods.]

    It's also a practical consideration as well: imagine if a flashlight sported one of those cool radiation warning signs

    41hgKiEoCBL._SX425_.jpg

    and you needed to wear a radiation suit every time you used one, or have a radiation safety officer present to decontaminate you after you were done using the flashlight.
     
  8. Jul 4, 2014 #7

    mfb

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    Visible light can injure or even be lethal as well, but the damage then comes from its heating effect - it can burn your skin (or eye, for example if you look at the sun). And the required intensity is orders of magnitude above the lethal dose for the more high-energetic radiation.
     
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