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Two days after North Korea said it successfully conducted a nuclear test, evidence that it really did remains sparse. A senior Cheong Wa Dae official said it may take some two weeks to accurately analyze the available data, and military sources say it will take between two and five days.
No geographic traces
Underground nuclear tests usually entail geographic changes such as sunken land or newly created big holes, but as of Tuesday afternoon, the KH-12 surveillance satellites had observed none where the nuclear test would most likely have been conducted, sources said. When the U.S. detonated a 100 kT (1 kT is equivalent to 1,000 tons of TNT) nuclear weapon 190 m underground, it created a hole 190 m deep and 370 m in diameter. Experts wonder why none have been seen in the North when even small nuclear weapons of less than 1 kT produce such changes.
KH-12 surveillance satellites focusing on the areas where North Korea¡¯s nuclear test could have been conducted, including Sangpyeong-ri in Kimchaek City, are capable of detecting even small changes as they are able to identify objects as small as 12 cm from an altitude of 500 km. However, it is possible that such changes have not been detected as the U.S. and South Korea have not yet identified the exact test site.
No increase in radioactivity
A variety of radioactive material is released no matter how small a nuclear test is, experts say. U.S. surveillance planes WC-135 and RC-135 and Japan¡¯s T-4 jet trainer which are flying over the East Sea to detect any radioactive material, and South Korea¡¯s terrestrial radioactive detector have not yet found any radioactivity, sources say.
It is possible that the detectors failed because the material is very sensitive to wind directions. Once any radioactive material is detected, it would confirm when the test took place.
The weak tremor
Another controversy is over the 3.9 magnitude of the tremor observed on Monday, which is lower than usual nuclear tests. Pakistan, India and China produced readings between 4.5 and 6 on the Richter scale when they carried out their nuclear tests.
Small-scale nuclear tests, however, could produce readings lower than 4, experts say. When a nuclear test with a yield of 0.1-0.5 kT is conducted, it produces readings lower than 4. The Korea Institute of Geoscience and Mineral Resources said the readings were between 3.58-3.7 on Monday, but the Ministry of Science and Technology adjusted it to 3.9 on Tuesday. An official with the KIGMR said this is too small to be considered a nuclear test.
The worst-case scenario -- a small nuclear weapon
It is possible that North Korea did test a small nuclear weapon. This is the worst-case scenario for South Korea because it means that the North succeeded in making it¡¯s a nuclear weapon small enough to be delivered by missile. However, experts doubt this. The Washington Post raised three possibilities. Either North Korea detonated a conventional weapon, or only some of the plutonium was detonated, or the country used a smaller amount of plutonium than usual. ¡°It could be that the detonation took place on a far smaller scale than North Korea expected or that it placed various buffer devices around the nuclear weapon and its power was observed to be smaller than actual,¡± an expert here said.
(englishnews@chosun.com )
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