hankyoreh

No signs of unusual radiation levels have been detected in South Korea after North Korea said it successfully detonated a nuclear device, the government said Thursday.

The Ministry of Science and Technology said none of the government's 38 manned and unmanned monitoring centers had picked up any spikes in natural radiation from Monday noon to Thursday morning. The usual levels of radiation in South Korea are 10-20 Micro-Roentgen (mR).

"The announcement is based on data collected around the clock," said Lee Mun-ki, head of the ministry's atomic energy bureau.

Detectors have been adjusted to pick up spikes in four key radioactive nuclides that can rise after a nuclear test has been conducted.

He said all levels of ruthenium-103, cesium-137, zirconium-95 and cerium-141 detected throughout the country during the period were normal and unchanged from the average in the past five years.

Lee also said authorities have taken rain water samples from Gangneung and Chunheon, where precipitation had been reported after the alleged test took place. The official said the results of the rain water test will be released Friday.

"If for some reason a level of more than 10,000 mR of radiation, which is the safety limit set by the United Nations' International Atomic Energy Agency, is picked up anywhere in the country, the government will issue immediate alerts," the official said. In such cases people will be told to stay indoors, avoid eating outside and avoid getting wet from rain.

On concerns that the test may have contaminated underwater reservoirs, the director general said past tests conducted in Russia and the United States did not cause contamination because the heat and pressure from the atomic blasts usually vaporized liquids.

He added that because the suspected site of the blast in North Hangyeong Province was 250-300 kilometers away from the nearest South Korean territory, the possibility of underwater reservoirs in South being contaminated was remote.

"Despite this, the government has started to collect weekly samples from underwater reservoirs in Seoul, Gangneung and Chuncheon," he said.

The official said Seoul was also looking into the possibility of radioactive particles seeping into the East Sea and that samples of the sea floor and water are to be collected and analyzed.

The ministry also said South Korea has leased a xenon nuclide detector from Sweden to enhance its capability to conduct specialized atmospheric tests. The equipment arrived in South Korea on Wednesday and is being deployed. Xenon gas is considered the definitive indicator of a nuclear test.

Independent experts, however, said that due to the decay period of xenon gas that can survive for a maximum 11 days after being released by a explosion, South Korea may not be able to pick up any traces.

Earlier in the day, the state-run Korea Institute of Nuclear Safety said southwesterly breezes of 2 meters per second have been blowing from North Korea from Tuesday, making it very hard for detection devices in South Korea to pick up any radiation.

Experts had said dispersion of particles as they travel through the atmosphere is a key factor that can make detection hard from long distances.

In addition, the ministry said a special monitoring task force chaired by the vice science minister has been set up and will coordinate monitoring for possible radioactive particles.

Seoul, Oct. 12 (Yonhap News)