uranium forecast by macquarie, page-29

U308wave, Average exposures aren't really an issue are they? I'm not suggesting the risk lies in the death of the whole population, its bumping into concentrations of the stuff that matters dopey!

Whats the population average for being crushed to death by some mining equipment. Pretty god damn low would be my guess, but, compare that to mine workers average and you can start to understand why mine site safety is an issue thats taken very seriuosly, (mostly!).

You say 5 - 6 Sv to kill you. Well below suggests 4.5 Sv of Polonium 210 may be enough, and that much exposure could be delivered by a particle weighing less than one millionth of a gram (0.089 micrograms). Not very much at all, me thinks you wouldn't see it coming while playing outdoors like ya mumma told ya, she should obviously have said get to your room and stuck into the books! lol ;-)

"The median lethal dose (LD50) for acute radiation exposure is generally about 4.5 Sv.[27] The committed effective dose equivalent 210Po is 0.51 µSv/Bq if ingested, and 2.5 µSv/Bq if inhaled.[28] Since 210Po has an activity of 166 TBq (4486.5 Ci) per gram[28] (1 gram produces 166×10^12 decays per second), a fatal 4.5 Sv (J/kg) dose can be caused by ingesting 8.8 MBq (238 microcuries), about 50 nanograms (ng), or inhaling 1.8 MBq (48 microcuries), about 10 ng. One gram of 210Po could thus in theory poison 20 million people of whom 10 million would die. The actual toxicity of 210Po is lower than these estimates, because radiation exposure that is spread out over several weeks (the biological half-life of polonium in humans is 30 to 50 days[29]) is somewhat less damaging than an instantaneous dose. It has been estimated that a median lethal dose of 210Po is 0.015 GBq (0.4 millicuries), or 0.089 micrograms, still an extremely small amount. [30][31]"

http://en.wikipedia.org/wiki/Polonium#Acute_effects

To be honest the problem is we don't really no whether there is such a thing as a safe exposure level. Its by no means cut and dry in either direction. It is highly likely that risk vs exposure does not follow a linear relationship.