A Silicon Valley exec recently traveled to Japan for business. He took a Geiger counter with him and measured radiation throughout the trip–including on his flights to and from Asia. Steve Jurvetson posted a graph on his Flickr stream. He writes:
One of his destinations was 50 miles from the crippled Fukushima Daiichi nuclear power plant. As a precaution, a colleague gave him a Geiger Counter so he could make sure it wasn’t getting dangerous as he approached the plant.
Maybe they assumed he would turn it on when he hit the ground… Instead, he logged the whole trip, and you can see the relative peaks of radioactivity.