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Hunt for nuke fallout steps up in Japan's skies

Publication Date : 14-02-2013


Several ministries have started observations and surveys to check whether airborne radioactive material created by North Korea's nuclear test might have reached Japan, although experts believe it is unlikely the Japanese will be directly affected.

The Environment Ministry said it had not detected any increase in radiation that might have been caused by the nuclear test as of midnight Tuesday. No radioactive materials were detected in Japan after North Korea's two previous tests.

"Today became a day when tensions rose for both Japan and the world," Defence Minister Itsunori Onodera said to Adm. Samuel Locklear, commander of the US Pacific Command, who visited the Defence Ministry on Tuesday evening.

They reportedly confirmed Japan and the United States would strengthen cooperation to respond to the nuclear test.

Earlier Tuesday, three T-4 trainer aircraft took off from three bases including the Air Self-Defence Force's Misawa Air Base in Aomori Prefecture to collect dust in the air over the Sea of Japan and Honshu. The planes trap dust in a filter on a collection pod installed on the bottom of the aircraft.

The samples were to be taken to the Japan Chemical Analysis Centre, the nation's only institute that specialises in analysing such substances.

Dust will be collected over several days for analysis at the Chiba-based institute.

Japan can measure radioactive materials that could have leaked into the atmosphere due to an underground nuclear test at two sites established within the framework of the Comprehensive Nuclear Test Ban Treaty (CTBT). As the amount of radioactive material that leaks into the atmosphere after a nuclear test is usually quite small, it will take several days to see results.

The CTBT observation sites are in Takasaki, Gunma Prefecture, and Onnason, Okinawa Prefecture. Extracting a small amount of radioactive material from samples takes at least 10 hours, and carefully measuring the concentration of radiation of the extracted materials will take from 11 to 24 hours. The data will be distributed to relevant institutions all over the world, and then it will be determined whether the radioactive materials were created by a nuclear test.

However, after North Korea's two previous nuclear tests in 2006 and 2009, no radioactive materials created by the tests were detected in Japan.

The Education, Culture, Sports, Science and Technology Ministry estimated that if any radioactive materials created by Tuesday's test leaked into the atmosphere, they would have arrived over Japan at about noon Wednesday.

"We announced the estimate as reference information so the monitoring of radioactive materials could be conducted effectively," a ministry official said. "There's no need to consider evacuation."

Effects on Japan unlikely

Most experts agree there is little chance the nuclear test will generate radioactive material that will reach Japan.

"Generally, radioactive materials are mostly confined under the surface if a nuclear test is carried out underground, so it's unlikely North Korea's latest test will have a direct impact on Japan," said Michiaki Kai, professor at Oita University of Nursing and Health Sciences and an expert in radiological health and radiation risk analysis. "However, there's little information available about North Korea's nuclear facilities, so we can't deny that a small amount of radioactive material, such as noble gas, could have leaked into the atmosphere. In that case, figures on radiation measured at sites across Japan would change over a wide area, so we should carefully watch for any changes in these figures from now on."

Jiro Inaba, former senior researcher at the National Institute of Radiological Sciences, said the test would not affect human health in Japan.

"Many details of the test remain unclear. However, it's impossible that it would have caused a large amount of radioactive material to spew into the atmosphere, as happened in past atmospheric nuclear tests by the United States and the Soviet Union. I can't say definitively, but I doubt there would be an impact on people's daily lives in Japan," Inaba said. "It's possible to know whether a nuclear test was really carried out by detecting radioactive noble gas and xenon, both of which are created during nuclear fission. Because xenon leaks up out from the ground, it is used to determine whether an underground nuclear test was conducted. However, the radiation dose caused by the test will be minute, so I think it's safe to say it won't affect people's health in Japan."


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