I'm glad to see your "comprehensive" list of radiation websites comprises ALL sides of the issue rather than one, conspiracy theory and all radiation is unequivically bad for you sites. Sarcasm implied.
Might I suggest a more neutral link by an accountable source:
http://www.nlm.nih.gov/medlineplus/radiationexposure.html
This is what the National Institute of Health has posted and contains lots of good information covering guidelines and effects of radiation exposure.
Is all radiation harmful? The jury is still out on this issue. There are biological reasons to believe it should be, radiation breaks up DNA molecules so it seems logical. This is called the linear-no threshold model and assumes that any dose is detrimental. However, like everything in the real world, things are often not as clear cut.
If you look at statistical studies done on areas with higher background radiation than others, there is an interesting trend that people living in regions with slightly elevated regions of natural background radioactivity (even by as much as a few rem per year due to natural Uranium or Thorium deposits). What is interesting is that rates of cancer are
lower and people overall are
healthier in areas with elevated background radiation.
Even more confusing is a study done on naval dock workers. The study looked at two groups of people: one that had come into contact with the spent fuel of the naval reactors and another group that did not. The interesting correlation is that cancer rates and overall death rate was statistically lower in the group that handled the waste than the other group to the point where it could not be just attributed to random chance.
Some biologists have even proposed a model of the cell where higher levels of ionizing radiation causes certain repair mechanisms in the cell to activate and fix up the DNA that would have otherwise have remained unrepaired due to carcinogens and natural errors in copying of the DNA. This theory is called radiation hormeosis and seems to be gaining some ground among the medical community. Picture it in terms of getting your required exercise to stay healthy.
I will point out that radiation hormeosis is not really a fully established theory yet and still needs a lot more study to show whether or not it works. There is still a bit of evidence on both sides of the coin with no clear winner at this point.
Regulatory agencies use the linear-no threshold hypothesis to assess risk because it gives a theoretical maximum of how many cases are possible even though they are often grossly overstated. For instance, if a million people receive one millionth of a lethal dose, then one person will die. Now logic and common sense says that if any person receives a millionth of anything at a lethal level they will not die. However, the LNT hypothesis calculates the maximum. So even still there is some common sense to the approach of LNT.
I'll get back to you Chernobyl. I do not have time right now to right a full out piece.