Question

There are many stories about radioactivity and the relative danger of it in the news lately, but very little actual information. The radioactivity levels around Fukushima Daiichi are high, but seem negligible in just somewhat removed locations.

The real danger seems to stem from ingesting radioactive particles. Just how likely is it for that to happen in any considerable distance from the reactor, say in Tokyo, and how dangerous for the human body is it really? How far can these particles travel in any dangerous concentration?

Answer 1

I would like to add that radioactive isotopes are a constant background in all natural environments, and more so in stone and concrete buildings. The relevant question is how much more than the natural background is the artificial radiation induced by human activities.

In a recent viewpoint in BBC news professor Alison gives relevant numbers. For example, the human body has about 50 becquerel per kilogram in the natural state. An interesting chart that puts radiation in perspective is here, and this is a graph from the scientist who provided the numbers for the chart.

So when you see animated maps of how the radiation is spread from Japan, read the scales. You will see that the numbers are within natural variations.

The immediate danger of death come for huge doses, look at the chart. Even for people next to the reactors there has been no such exposure. There are long term effects of ingesting or breathing in isotopes for the people in the region, which have to do with a larger cancer rate over twenty or thirty years. The rest of the world is nowhere close to such levels of exposure.