While the discovery of 195 becquerels of strontium 90 in the rooftop sediment has fueled concerns that leaked radiation may have spread further than the government had expected, the officials said the city office is carefully examining where the material came from.
This is the first time strontium at a concentration of over 100 becquerels per kilogram has been found beyond 100 km from the Fukushima plant. The strontium 90 was detected in Yokohama, south of Tokyo, by a private agency that conducted the test upon the request of a resident.
Strontium 90, with a half-life of 29 years, has been detected at concentrations roughly between 10 to 20 becquerels at various places across Japan prior to the nuclear crisis triggered by the March 11 earthquake and tsunami. Read More