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I've heard that the level of "background radiation" is not the primary concern in a radioactive accident; instead the radioactive particles emitting the radiation, and the absorption thereof, are the primary concern.

I've not heard any mainstream scientists mention this (the only vaguely related source I can find online is here), so I'm extremely hesitant to believe it. Is it true?

Edit

By "background radiation", I meant the level of radiation picked up by radiation detectors. It was a poor choice of words.

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    What do you mean with "background radiation"? Usually that expression means the radiation that is constantly present in the environment. Background radiation exists even without a nuclear accident happening (e.g. the banana in you link). Maybe you are confusing "background radiation" with "escaped radiation after a nuclear accident"?
    – Oliver_C
    Commented Mar 25, 2011 at 9:55
  • @Oliver_C I have updated my question.
    – ClosureCowboy
    Commented Mar 25, 2011 at 23:54
  • First: look up the difference between ionizing and non-ionizing radiation. Then realize just how good our detecotrs are (having something detected is something on the order of 10^-70 the amount for health issues). Last: radiation source doesn't matter if it is ionizing ... the LD50 covers rates of fatality/illness.
    – iivel
    Commented Mar 26, 2011 at 2:16

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The US Environmental Protection Agency is clearly more concerned with ingestion than direct exposure: see http://www.epa.gov/radiation/understand/pathways.html

Skin will actually block most of the alphas and the neutrons. X-ray and gamma rays of course would go through the skin.

Remember, the radiation travels in straight lines from the source and is typically absorbed when it impacts a solid enough target. It affects the area around the source. Radioactive particles themselves create radiation. So the propagation of radioactive particles by wind or other vectors is the primary method that the danger of radioactive exposure can spread from the immediate area around the source.

If someone ingests radioactive particles either through air, food, or water, it will continue to irradiate their body from the inside as the material decays. This is clearly worse than a temporary exposure.

If someone is exposed to a source of rays but not radioactive particles, typically their skin and clothing will provide protection from some kinds of rays, but not all. When they are removed from the source of the rays, there is typically no residual radiation.

It is worthwhile to realize that there is a background radiation from outer space that is not absorbed by the atmosphere. Therefore, unless you live in a lead lined bunker or under the ocean you can not completely eliminate exposure to radiation. Levels of radiation comparable to this background level are considered acceptable.

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  • "Skin will actually block most of the alphas and the neutrons" Er...alpha, yes. Neutrons, not so much. The secondary protons produced by hot neutrons are stopped by relatively little matter, but the neutrons themselves are very penetrating (because they interact relatively weakly), and they can produce those secondaries inside the body. Moreover, once they thermalize (and stop producing secondaries) they either capture or decay producing mostly gamma which are also penetrating.
    – dmckee --- ex-moderator kitten
    Commented May 22, 2012 at 21:40
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To supplement Paul's answer, direct radiation from your source would obey Inverse-square law. Which means it's mainly a concern in the immediate vicinity of the source and greatly decreases with distance. Whereas radioactive particles can be distributed VERY widely with the wind (or water in water table or river).

As a specific example, there are IIRC 57 confirmed deaths from effects of direct radiation from Chernobyl. Compare that to issues from particles that were blown all over Russia/Europe (which were less severe but more numerous) - I believe Chernobyl Wiki has enough relevant statistics.

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