I realize there's been a lot of free advertising for radiation detector companies out there and rightfully so. Unfortunately, it seems that a lot of people (even people outside of Japan) are purchasing these elaborate detection instrumentation that is frankly, overkill. As a health physicist, I've been doing my best to try and calm the American & Canadian population and inform as much as I can. I just want to state for the record: Purchasing sodium iodide pills here in the US is absolutely pointless. There is no possible way significant amounts of radioactive iodine will ever reach the west coast.
Now, for those interested in Japan's situation, according to the NewScientist, radioactive iodine-131 was discovered in Spinach grown at the Fukushima prefecture. As much as 15,020 becquerels of radiation per kilogram. Let me just say, that's not an insignificant amount. Here in the US, the Nuclear Regulatory Commission allows radiation workers to orally ingest 30 uCi of iodine-131 (approximately 1,110,000 becquerels) per year. This amount corresponds with the 50rem per year or 0.5Sv per year limit to the thyroid gland here in the US. That means, I would have to ingest 73kg of spinach or leeks from the prefecture affected in an entire year. Let's put that into perspective... According to the FDA, the average American eats 1500lbs of food per year (approximately 680 kg). If I'm doing my math correctly, spinach or leeks would have to account for about 10.7% of my daily intake of food (in mass) in order for me to reach my legal limit. Typical recipes call for about 2lbs of spinach to serve 4-6 people. That's about half a pound of spinach per serving during a meal (~230g). Think about it people... That's a lot of spinach in a year! Amounts to about 321 radioactive spinach salads in a year!
In terms of water contamination, it was reported that they measured 965 becquerels of radiation per kilogram. Average person drinks about 2L or 2kg of water in a day which amounts to 730kg of water per year. In order to reach my legal limit, I would have to drink 1,150kg of water in an entire year, nearly doubling my normal intake. I don't even want to get into the fact that iodine-131 has an 8 day half life i.e. 1000 becquerels would decay to 500 in 8 days! The Japanese government is very cautious and conservative in their limits to the public and they should be! But we always have to put things into perspective.
Back to the tech stuff! Actually, I almost took a position in product development for the company that manufactures the radiation sensitive film in Wayne, NJ. I'm not exactly endorsing this product (royalties would be nice though) but this is exactly what I would recommend for the general population.
Laurus Systems RADView webpage.
In terms of having an easy to decipher radiation detection device, film dosimeters are by far the simplest way of determining any danger to yourself or your household. These little devices are about the size of a credit card. These cards have a film in it that is sensitive to ionizing radiation and will darken the greater the radiation absorbed. Keep in mind the time factor as these do not subtract the annual background radiation we receive (240 mrem per year - world average). The technology isn't very sensitive but it is extremely user friendly and easy to read. They even made one for fire fighters in the Fukushima Daiichi plant as they hose the reactors down to cool the fuel rods!
Anyways, please visit the website and try to read articles from reputable sources that know what the heck they're talking about. Remember, there are no stupid questions; feel free to post any questions or comments.