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Being hit by a fast particle - What would happen?

  1. Feb 7, 2009 #1
    I believe we are being hit by some rays which approach the speed of light. Although I'm not sure.

    However, what would happen if I was standing inside the LHC and one of their protons which is going 99% c hits me in the head?

    How about an atom of iron traveling that speed? How big/dense would something need to be before it kills me traveling at 99% of the speed of light.
  2. jcsd
  3. Feb 7, 2009 #2
  4. Feb 7, 2009 #3


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    Note that there is a huge difference in energy between a particle traveling at 99% speed of light and one traveling at 99.9999991% of light at LHC.

    The Bugorski case is probably the only case where someone has actually been hit (and that was a small accelerator), but accidents with equipment does happen. I've heard of one case at Fermilab a few years ago where the beam hit a detector and essentially drilled a hole in it. There aren't that many particles in the beam so the mass is very small, but each particle carries a LOT of energy.

    Hence, if you were to get hit in the head at LHC my guess it that you would die pretty quickly.

    And yes, we are constantly being hit by particles from space but the atmosphere protects us from most of it.
    It is known that e.g. pilots, air stewardesses etc that spend a lot of time at hight altitudes have a somewhat increased risk of cancer, although it is not quite clear if this is related to cosmic radiation or not.
  5. Feb 7, 2009 #4


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    It's not the question of being hit by such particles, but more of a "coupling strength". For example, we are being bombarded by cosmic neutrinos that travel essentially at c all the time. Yet, these are particles that interact very, very weakly with matter such that it can pass through the earth without even noticing the earth is there. So being hit by such a thing certainly produces no significant effects.

  6. Feb 7, 2009 #5


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    Aircraft crews have high probability and incidence of cataracts, as well as certain cancers. Astronauts also have a greater risk of occular problems.

    The effect of radiation depends on where in the body, or what vital organ is affected, and what dose. If Bugorski's brain stem or spinal cord had been irradiated, he would have died very quickly, perhaps instanteously. He was probably irradiated in the cerebellum (front/forehead) and face. Also, it was not just one proton, but a current of protons. In addition to ionizing atoms/molecules, the protons or other high energy particles displace nuclei which cause secondary ionizations over tens of microns from the particle track. Add to this the X-ray and gamma radiation (brehmsstrahlung).

    In addition, high MeV particles can cause spallation reactions in which nucleons (e.g. neutrons, protons, and even deutrons, alphas, . . . . ) are ejected from the nuclei.

    Standing in the path of LHC beam would likely be fatal.
  7. Feb 7, 2009 #6

    Vanadium 50

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    Interesting. The occupational limits for radiation exposure to the lens of the eye are 3x higher than the whole body dose. I had always assumed this was because the eye was more radiation tolerant than other tissue (e.g. bone marrow) but maybe this is the wrong conclusion and I am being misled by two factors: in a whole body exposure, many different things can go wrong, and cataracts are less serious than, say, pancreatic cancer.
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