One of the things that has come up again and again when discussing whether or not the MotoGP race should go ahead at Motegi is the levels of radiation that riders, teams, journalists and fans might potentially be exposed to, and the related dangers such exposure might bring. As radiation is one of the most poorly understood - by the general public, at least - of risks that humans are exposed to, it is helpful to visualize such exposure in some other way than with raw numbers alone.
In the aftermath of the Japanese earthquake and tsunami, and the severe damage to the Fukushima nuclear plant, the extremely entertaining science and computer cartoon blog XKCD produced a handy chart illustrating the exposure produced by a range of activities. Here's the chart (click on the chart for a full-size, easy to read version):
For comparison, current levels of radiation at Mito - the town where most of the riders and teams stay during - is 86 nanosieverts or 0.086 microsieverts (µSv) an hour (measured at 1am local time on July 20th, 2011). Over the course of a six-day stay in the region (though teams will often stay for just five days), a person would receive just under 12.4 µSv of radiation, about 60% of the dose of a single chest x-ray. By comparison, radiation levels in Chemnitz, where the teams generally stay during the German Grand Prix at the Sachsenring, were about 100 nanosieverts, or 0.1 µSv an hour. Staying in Chemnitz for 6 days exposed the teams to 14.4 µSv of radiation.
Naturally, the background radiation levels are just one part of the overal risk assessment of going to Motegi for the Japanese MotoGP round. There are other threats: another earthquake in the highly geologically active region and along the now highly active fault could cause further serious damage to damaged Fukushima nuclear plant; the efforts to stabilize the situation at the plant could fail dramatically, release large quantities of radiation into the atmosphere; or another earthquake could cause structural damage in the buildings the teams are staying, potentially endangering those in the building at the time. However, what the above the chart shows is that the background levels alone are not cause for concern.
For a full report on the risk of developing cancer from radiation, see this report by the World Health Organization's International Agency for Research on Cancer. And for a comparison, see the report on the cancer risks of smoking from the same body.
Thanks to Douglas Edmiston for the links to radiation levels in Japan and Chemnitz, and thanks to Randall Munroe for assembling the radiation chart, and especially for putting together the fantastic and hilarious - in an intensely geeky sort of way - xkcd.com website.