Part of what has been frustrating me is news harping about exposure levels. Levels are X times greater than normal. I know enough to know it is more complicated than that. And X times greater than extremely low and barely detectable may still be insignificant. I defer to those who really know--like someone who works in nuclear medicine and has a background in naval reactor operation, for example.
I keep waiting to hear that carbon-14 has been detected, and the flooded areas around the power plants contain hydronium hydroxide.
Exactly my frustration with the "reporting" going on.
Forgive me for lecturing, but if I may, a little RadCon 101 here. This is ultra- ultra-condensed from several nuclear engineering and USN training courses. Oversimplifying but the gist is correct.
Natural background radiation that you get sitting at home is about 0.5 to 1 mR/day (0.0005 to 0.001 Roentgen).
Roughly, 1 Roentgen (1 R) is about 1 rad, which is about 1 rem. These are all similar but not identical units of radiation exposure to people. 1 R ~ 1 rad ~ 1 rem. 1 mR ~ 1 mrad ~ 1 mrem.
So, on average, each person in the US gets maybe 300 mrem per year. A CAT scan will give you maybe 1-4 rem to the part of the body that got scanned. A chest x-ray will give you about 0.005 rem (5 mrem). That is, a chest x-ray is as much radiation exposure as sitting in your house for a week.
Federal (and most U.S. states) regulate radiation exposure to workers and general members of the public as a matter of safety. The exposure limits, how much you're allowed to get, are very conservative. Members of the public are not allowed to get more than 100 mrem per year from all sources of radiation, other than medical. If an industrial concern say wants to get a radioactive materials license and do stuff with it, part of the licensing process is for them to demonstrate that whatever doses teh public gets from their stuff is much less than 100 mrem per year. As a radiation worker, I'm safely allowed to get up to 5,000 mR (5 rem) per year. Contrary to what most people think, I'm allowed to get a LOT more occupational radiation exposure now as a civilian than the US Navy allowed me to get as a military nuclear operator. Try convincing someone who watches CNN of that, though.
Acute radiation exposure: this has HUGE error bars on it, there is a lot of uncertainty due to person-to-person radiosensitivity. But, it would take an acute (all at once, in less than a couple of hours) whole-body exposure of about 25 rem (that's 25,000 mrem) to actually cause enough changes to your blood and bone marrow that a lab could even detect the changes and tell that you'd had even some radiation exposure.
Getting about 100 rem (or about 100 R or about 100 rads, or 100,000 mrem) to your whole body is enough to cause radiation sickness. Nausea, vomiting, possible loss of hair, stuff like that. Your bone marrow (which produces your blood cells) and GI tract are messed up. If all you got was a one-time exposure like that, you should pull through, with rest and medical care, but it'll take at least a month to heal the damage and get sort of back to normal.
A whole-body exposure of 400 rem is more serious. About half of the people who get that much in one shot will die within a month or so. More of them would survive, if lots of medical care is available. If this kind of exposure happens only to you and there's a hospital nearby, your chances are a lot better than if 10,000 people got this exposure and there's not enough acute hospital care for everyone.
An acute dose of about 1,000 rem is even more serious. Almost everyone, or everyone, who gets that much in one shot will not survive, even with an ICU unit level of care. Massive damage. A young, strong person with loads of acute medical care might theoretically pull through. If it happened to a lot of people, uh uh. The Chernobyl firefighters who valiantly tried to extinguish the reactor on fire got several thousand rem each in an hour, and died within days.
So, now, IF the damned reporters would report facts about exposure levels in mR/hr, you might get a little useful information. Generally, the venting operations going on release radioactive material that quickly disperses. The radiation exposure someone standing at the power station fenceline would get is usually pretty darn small, even in an accident like this, unless the roof of the containment just disappears like happened in Chernobyl. That's not what the explosion was in Japan, even though it's called a reactor building. At Three Mile Island, they had to vent some radioactive gas from inside the containment. The dose to someone standing on the TMI fenceline ould have been about 50 mR, if any civilians had been still there when this venting occurred.
From what I've just told you, you can see that 50 mR (0.05 rem) is no big deal at all in terms of exposure. It's way more than normal in terms of "you were exposed to 50 times the daily background level" but it's still not much exposure. Our own government very safely allows you to get twice that each year. Me as a radiation worker? I'm allowed to get 100 times that much, safely, each and every year. I've never gotten that much, and you don't just go get radiation exposure for no reason, but 50 mrem isn't anything to worry about if that's as high as the exposures got. That was the theoretical maximum a member of the public could have gotten from the TMI accident. The actual maximum received was much less, because the only members of the public around were as far away from the TMI plant property line as they could get!
There's not much hard info coming out of Japan on exposure kind of stuff, mostly because the radiation exposures to people have been very small as far as I know. The main concern is that if they have an uncontrolled release of radioactivity (like breach of containment, which hasn't happened and I don't think is expected to happen), then the exposures to people around there could be very large, hence the 12 mile evacuation.
Hope that helps, I'll cut this off for now. I've been typing this while at work for the last hour, preparing a linear accelerator for treating patients with radiation. (probably delivered something like 50,000 rads to a piece of plastic this morning in the past hour, like we do every morning, to get it all tuned up and running). You wouldn't want to be that piece of plastic! We give significant doses of radiation to treat cancer, and radiation patients can suffer some of the same side effects from radiation, depending on what part of the body we're treating. The treatments work with relatively few side effects through because cancer patients are closely monitored during their treatments, because we're treating limited portions of the body instead of the entire body, and because we control the rate at which radiation is administered to allow the body to heal itself in between treatments.
(UPDATE)
http://www.swissinfo.ch/eng/news/international/Radiation_leaps_after_Japan_plant_blasts,_warnings_for_Tokyo.html?cid=29698946Ok, finally some numbers. Right outside the reactor building has been reported at 400 mSv per hour. I hate SI units here by the way, give me the old-time U.S. units of Roentgens, rads, and rems. One Sievert (Sv) is 100 rem. thus 400 mSv is 40 rads per hour. See above for how much exposure 40 rads would be. Nutshell - if you stood there for a little over a half hour, you'd start to have some detectable blood changes from the radiation. In two and a half hours, you'd get enough to probably get some radiation sickness. You would however reach your U.S.-allowed limit of 100 mrem in just a few seconds. I as a radiation worker would get my annually-allowed 5 rem or 5 rads in about 1/8 of an hour (5/40), or 7-8 minutes. Ok, don't stand right outside the reactor building until or if they get a handle on the situation inside the building.
This is RIGHT OUTSIDE THE BUILDING, mind you. The exposure rate, rems per hour, drops off very quickly as you move away from the source of the radiation. Levels outside of the plant property are elevated but still within the legal limits I mentioned, per a news story on drudge right now (sorry don't have the link handy). That 100 mrem per year (0.1 rem per year) I mentioned is generally what is internationally recognized as an exposure limit for members of the public, or "civilians" if you will.
If it makes any difference, we/I do these calculations frequently in cases where we implant patients with radioactive material and then tell the nursing staff, and anyone visiting the patient, where they can stand and for how long. Dose = doserate x time. Therefore time = dose / doserate.
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