Just a sort-of quickie here, to clarify some of the worst propaganda coming from the nuclear industry, government 'officials' and assorted others about the radiation dangers coming from the Fukushima nuclear reservation.
First and foremost, it needs to be understood by everyone that potassium iodide doesn't "protect people from the effects of radiation," as is being ubiquitously reported by the world's media. It only protects against possible excess radiation to the thyroid gland upon exposure to a single isotope.
Potassium iodide is a stable iodine supplement. It provides enough stable iodine to 'saturate' the thyroid, which means that radioactive iodine won't find its way there to cause thyroid cancer. That's all it does. If you aren't exposed to radioactive iodine, then you can get an ample supply of stable iodine from your diet. Sea vegetables (seaweed) and ocean fish/shellfish are excellent sources. If you live near a nuke you can buy dried kelp capsules as a "metabolic supplement" at the drug store's natural supplement aisle, take 2 or 3 with meals during the day, and not have to worry. Not even from the amount of iodine-131 that might reach you from Fukushima.
But iodine-131 is not the nastiest isotope in the plume. Potassium iodide doesn't help in the least when it comes to cesium (your body uses it as potassium) or strontium (used as calcium), and doesn't do a thing against the ionization of atoms in your cells if these isotopes decay on their way through your body (or in your lungs). That radiation will still damage sensitive internal cells as radiation tends to do. The ONLY real protection against radiation damage is not to be exposed to it.
Second, I think it's important that people concerned about possible exposure understand the difference between "radiation" and "contamination." The plume from Fukushima isn't dangerous because it's emitting a lot of "radiation." It's dangerous because it comes with a veritable invisible cloud of radioactive particles - like dust - that can give off their radiations point-blank when they get to you.
The danger to workers at the melting reactor plants - and helicopter pilots trying to re-flood the pools - is coming from high energy gamma and neutron radiation being emitted in all directions by the melting fuel. The kind of intense radiation that made shadows on the wall at Hiroshima - vaporizes people (and other things) if it's intense enough. This is NOT the radiation they've been measuring at distances from the plant.
What they're measuring in Tokyo and other places is the radiation being emitted by radioactive particles suspended in the plume or falling out of it ("fallout"). Moreover, what they're measuring is gamma - like with a geiger counter - not beta or alpha radiation which are 10 and 20 times worse, respectively, for biological damage if they're inside you. Gamma goes right through clothing and bodies, ionizing atoms here and there on its way through. Beta and Alpha are particulates of matter. Clothing, skin, a face mask will render protect against these forms of radiation. When 'authorities' say radiation from the plume isn't particularly dangerous, they're telling a deceptive semi-truth. It's not the exterior beta/gamma radiation dose from the plume that will most harm people, it's the interior dose from the contamination IN the plume.
Once an isotope is inside your body - in your lungs or nasal passages or digestive system - the beta and alpha (and gamma) emitted by the isotope when it decays bombards sensitive internal tissues up close and uncomfortable. If the isotopes are among those the body cannot distinguish from stable elementary isotopes, you may end up with a concentration of isotopes in an organ or near your bone marrow where the radiation can do great - eventually fatal - biological harm.
Don't let them fool you. The "minimal dose" they may (or may not) report if the plume comes to a neighborhood near you is indeed minimal. That doesn't mean it's not dangerous. Your concern should be with the contamination in the plume, which you definitely do not want in your body. For as long as there is measurable excess dose in your neighborhood, take all proper precautions. Think of it as invisible - but deadly - dust, and treat it accordingly.