Now that we've discussed (probably in way too much depth but I'm a geek and I can't help it) what radiation IS, it's probably really damned obvious already when to panic and when to say 'whoopee'. But I'll go over it anyway 'cause, well, I'm a geek.
The husbeast and I were kicking around ideas last night on how best to communicate this bit, and we discussed several analogies used by the military and I finally settled on the one that had made the most sense to me when the hub was explaining it, back in the day when I was deciding when to panic: Shit, and stink.
Yes, of course I can work a four letter word into a discussion of radiation and how it works. It's me.
Referring to yesterday's lesson, we'll go with uranium for our example. Uranium would be the shit. The alpha particle radiation put off by the uranium would be the stink. Stink is just stink; but if you get shit on you, you're in trouble. In formal terms, this means that if you were to get hit by some alpha particles put off by uranium, it would be radiation exposure. If you inhaled, ate, or otherwise wound up with uranium stuck to or inside your body, it would be radiation contamination. The husbeast does radiation safety as part of his job. According to him, standard procedure is to do swabs of the mouth and nose and test; if there's radioactive material in the swabs, THEN people freak out. Otherwise, as he put it, "heck, if it's on your skin, you can usually clean it up with soap and water". Alpha and beta particle radiation emitted from a source outside your body is stopped by your skin; wash your skin, and the problem is solved. Once the particle-emitting source is inside your body, though... then, THEN you've got a big problem. One nobody really knows how to treat. Isn't that fun?
Now you understand why most people who study the stuff are so casual about the term radiation, or at least want to know what kind before they spaz out.
For the average citizen who doesn't work at a nuclear power plant or a research lab/medical facility using radioactive isotopes, the opportunity for radiation contamination is about nil. Radiation exposure, sure. You get that all day, every day, from cosmic rays and sunshine and the radon gas in your basement. Contamination? That's a whole other story. The only thing I can think of is if you ate the interior of your smoke alarm. Even then I'm not sure smoke alarms contain enough alpha-emitting isotopes to kill you. You might have to eat a couple smoke alarms. (Smoke alarms need a small amount of Americium 241 to operate. It emits alpha particles and if left inside the smoke alarm and shielded, is safer than an afternoon of sunbathing. A discussion of risks and statistics available here.) Personally, I think if you're crazy enough to eat the inside of a smoke alarm, you've got bigger problems than radiation contamination.
Gamma rays, cosmic rays, and neutron radiation are a whole other ball game. Their mechanisms are slightly different, but the effect on the body and how to prevent said effect is about the same, so I'm lumping them all together. These are the zoomies that will go right through you, knocking off bits of atoms that make up your cells. In the case of neutron radiation, it can do fun things like create gamma rays when it runs into things, or turn atoms in your body into radioactive isotopes, so it's like from-a-distance particle radiation contamination. The only way to protect from this stuff is shielding. Water, cement, lead, some specialized kinds of glass, and some plastics all work. Those big tanks of water seen in video tours of nuclear reactors? Yup. Not only is it a coolant, it's shielding, too. Clever, no? Just like particle radiation, average citizens get the majority of their gamma, neutron, and cosmic ray exposure from natural sources like sunshine and, of course, the amount of it you are hit with will decide whether or not you should panic. Our bodies are used to constant low-level radiation, known as background radiation. A big blast and you're dead.
The Chernobyl accident is probably the best example of when things go wrong. One of the reactors exploded and then caught fire (why is still hotly debated; short story, they were fucking around to see what would happen). Massive amounts of radioactive material was barfed up into the atmosphere, into the ground water, and over everything downwind in the form of radioactive soot from the fire. The Soviet Union claims that 47 emergency workers and less than ten others were killed directly from the accident, to which I and most others say "my ass". But just like radiation exposure/contamination on a personal level, it worked the same way for the soil. Radioactive material (the shit, not the stink) got into the soil, and from that, it is now in every plant that grows on the soil, and then on into any creature who eats the plants. So the entire food chain is contaminated. As for radiation exposure (the stink), no one's quite sure what the levels were, because all the sensors maxed out; sort of like how your car's speedometer only goes to 120 but the car can go faster. However, the radiation was so bad that it set off warning alarms at another nuclear power plant in Sweden, and it was only after that the Soviet Union began to admit that, well, yeah, they'd sorta blown up a nuclear reactor.
But, anyway, my original point was, just like the other examples, the problem with Chernobyl was the massive amount of radioactive dust and soot put off by the explosion and fire. Breathing it led directly to radiation contamination and we're back to 'when to panic'. Incidentally, wine snobs refuse to drink any wine made in Europe after 1985. The explosion happened in April of '86 and according to them soil contamination has ruined every vintage since then. I'd be interested to try a comparative tasting and see if I could tell a difference.
To summarize. Radiation exposure happens all the time and unless it's massively high amounts - almost impossibly high for average citizens - you scrub down with soap and water, keep an eye out for skin cancer indicators, and otherwise forget it. Radiation contamination, get yourself to a hospital and hope for the best. There's no real treatment, just comfort care. Though contamination is also nearly impossible for average citizens.
Bottom line, get the hell out of that tanning bed, and don't build a breeder reactor in your garage, no matter how much fun it sounds like. (Besides. The NRC will show up and I have it on good word that those guys have NO sense of humor at all.)
(Okay. One last comment on the safety of nuclear power plants. I'm not saying they're safe, but I will say it's all relative. We had a spill at a 'clean coal' plant here in the US last December that dumped heavy metals into a major watershed and contaminated a massive area with crap like arsenic, thallium, lead, and mercury. The only clean power we have at the moment is wind and tidal/water, and geothermal - even those create a small amount of mess during the process of manufacturing the power plants. Is depleted uranium worse than coal ash sludge? You be the judge, but personally, I think one's as bad as the other.)