High cesium levels detected as far away as Gunma Prefecture

Radioactive cesium from the Fukushima No. 1 nuclear power plant has spread more than 250 kilometers toward the southwest, reaching as far as Gunma Prefecture, the science ministry said.

The Ministry of Education, Culture, Sports, Science and Technology has been measuring contamination levels in each prefecture in eastern Japan, including Gunma Prefecture from Aug. 23 to Sept. 8 using prefectural government helicopters.

According to the measurements released Sept. 27, most of the radioactive cesium first spread about 60 km northwest from the Fukushima nuclear plant, then changed course and spread to Tochigi Prefecture and further to Gunma Prefecture.

A plume of radioactive materials was carried by winds along the mountain range and then fell to the ground, according to ministry officials.

In Gunma Prefecture, the largest amount of cesium-137 accumulated in the northern part of the prefecture. Cesium-137's half-life, the period it takes for materials to be reduced by 50 percent, is 30 years.

The radioactive accumulation reached a range between 100,000 and 300,000 becquerels per square meter in a mountainous area encompassing the cities of Midori and Kiryu in the eastern part of the prefecture, about 180 km from the Fukushima nuclear plant.

Even in areas in the western part of the prefecture, which are located about 250 km from the Fukushima plant and border Nagano Prefecture, the accumulated radioactivity exceeded 30,000 becquerels.

In the aftermath of the 1986 nuclear accident in Chernobyl, areas where radioactivity levels exceeded 37,000 becquerels were designated as contamination zones.

In mountainous areas of Gunma Prefecture, where accumulated cesium amounts were quite large, the radiation levels were 0.5 to 1.0 microsieverts per hour. In other areas of the prefecture, the radiation levels were less than 0.5 microsieverts.

The criterion that requires removal of radioactive materials from schoolyards is more than 1.0 microsieverts.

The ministry has released the results of measurements in each prefecture on its Japanese website: http://radioactivity.mext.go.jp/ja/1910/2011/09/1910_092714.pdf.

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Cesium detected in a Miyagi boar

SENDAI — Radioactive cesium more than four times the safety limit has been detected in the meat of a wild boar killed in Kakuda, Miyagi Prefecture, officials said.

It is the first time radioactive contamination exceeding the limit has been found in a wild animal or bird in the prefecture, the officials said Friday.

They said they will ask residents not to eat meat from wild animals or birds.

The meat of the boar, which local hunters caught in the mountains in Kakuda on Aug. 7 as part of a city extermination request, was found to have 2,200 becquerels of cesium per kilogram. The provisional safety limit is 500 becquerels per kg.

KYODO

The science ministry has published a map on cumulative radiation estimates and hot spots five months since start of the crisis at the Fukushima No. 1 nuclear plant.

In giving estimates for 50 locations in the no-entry zone for the first time, the ministry said Friday a spot in the town of Okuma, 3 km southwest of the plant, had an estimated accumulative radiation of 278 millisieverts.

The annual radiation exposure limit for humans is 1 millisievert.

The government has urged people living in areas around the plant, where annual exposure is likely to exceed 20 millisieverts, to evacuate.

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Radioactive isotope, maybe from Fukushima, detected, but ... - Los Angeles Times

 
Very small amounts of a radioactive isotope of sulfur, believed to have traveled across the Pacific Ocean from the Fukushima nuclear plant in Japan, have been detected in La Jolla, Calif., by UC San Diego scientists.

But there's no need to worry: The amounts are nowhere near enough to cause health problems, researchers said.

Senior author Mark Thiemens and his team keep tabs on levels of sulfur-35 as part of their climate research. Readings collected shortly after the March 11 tsunami in Japan indicated that there were 1,500 atoms of sulfur-35 per square meter of air in La Jolla, a significant increase over normal levels.

The UCSD team interpreted the bump as the result of a reaction that would have occurred when plant workers used seawater to cool overheating reactors at Fukushima.  Neutrons from the reactor core would have reacted with chlorine in ocean water to create radioactive sulfur, Thiemens said.

"The levels we observed are in no way harmful in California," Thiemens said.

The group reported the measurements Monday in the journal Proceedings of the National Academy of Sciences.

Thiemens and his colleagues use highly sensitive instruments to detect the minuscule amounts of radioactive sulfur that circulate naturally in the atmosphere.  That they detected a bump in levels of radioactive sulfur was "not surprising," said Kai Vetter, who teaches radiation detection at UC Berkeley.  Vetter's lab has been tracking incoming radiation from Japan and has reported upticks too -- though again, nothing that would pose a danger to people in the U.S.

But Vetter and other nuclear engineers questioned elements of the research, which used the readings taken in La Jolla to extrapolate the amount of neutron leakage from the Fukushima plant.  Elmer Lewis of Northwestern University and Michael Golay of MIT were unconvinced that the radiation in question even originated at the nuclear plant.

Edward Morse, of UC Berkeley, said that the traces of radioactive sulfur probably originated at Fukushima, but he took issue with the team's final calculations.

"They're not nuclear engineers," Morse said. "They were a little out of their depth."

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-- Eryn Brown

Photo: Tsunami waves approach tanks of heavy oil for the Unit 5 reactor of the Fukushima Daiichi nuclear complex in Okuma, Fukushima Prefecture, northeastern Japan, in this March 11 photo released by Tokyo Electric Power Co. The waves unleashed by a magnitude-9 earthquake destroyed backup generators for several reactors' cooling systems, and the nuclear cores in three reactors melted. Credit: AP Photo/Tokyo Electric Power Co.

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