Yesterday I read this article in the Japanese Times about recently discovered radiation in Tokyo, Japan. The hotspot, an abandoned house, was found 200 km from the crippled Fukushima No. 1 and thus not likely to be caused by it. The radiation was also not likely to be natural because the ground did not have a high radiation.
2.707 microsieverts per hour were measured, on a yearly basis that would be 14.2 millisieverts. To give you an idea in Belgium the 4 millisieverts is the average received dose in one year. This level of radiation is not dangerous in the short term but children are more susceptible to the effects of radiation and because of a school nearby residents are concerned.
The contamination was likely to be from radium-226 which is not used in nuclear power plants.
This morning luckily the mystery was solved. Under the floor of the house they found bottles and test tubes filled with radium-226, a substance that can be used in luminous paint. Some of the bottles were labeled with ‘Nihon Yako’. Yako means luminous so the name could possibly be of the name of a luminous paint company.
The owner of the abandoned house is a 90-year-old woman who lived there until February. She says she had never seen those bottles before. She lived there since 1953 and slept 2 meters away from the bottles. The ministry estimated that she may have been exposed to 30 millisieverts per year. A dose that can be dangerous over a long period of time.
The article of the Japanese Times (in English) you can find here.