Updates to this report are available here.
"Updated on March 21, 2011 21:20 (JST)(Japan Standard Time) nGy/h (nano- Grays per hour)Realtime radiation data collected via the System for Prediction of Environment Emergency Dose Information(SPEEDI) These Results are the maximum values of the space those rate distributions shown from local governments in the latest updated date and time.
Not surprisingly, Miyagi , Fukushima and Ishikawa are completely N/A, as every single reading is Under Survey, may be unavailable sensors because of Tsunami (or maybe censored?)."
Background radiation comes from many sources, including medical x-rays, radon and cosmic rays as the usual suspects. Radon is a decay product of the uranium series, and decays by emitting an alpha particle. The direct parent of Radon is Radium, which emits gamma and alpha particles. Radon gas has different levels of concentration in buildings and can vary considerably.
In the cases from around the world, in normal areas, the dose rates were less than 100 nano Grays per hour (0.01 milli rem).
Those in Japan who can take reliable radiation readings and report them to a central independent source can do so here.
