The average yearly background radiation in Boston is 300 millirem, which is 3 millisieverts.(ref: http://tech.mit.edu/V113/N65/radchart.65n.html).This site – http://chottomatte.net/2011/03/16/tokyo-radiation-levels-daily-updates/ is reporting the daily radiation levels in Tokyo. Today’s Tokyo average radiation level, while higher than the Tokyo average, averaged about 0.25 microsieverts/hr.
That’s 2.19 millisieverts per year, or just 73% of the background radiation of Boston.
In other words, the year-round natural background radiation of Boston is 37% higher than today’s higher-than-normal radiation level in Tokyo. I’m staying here! doug