Dozens of monitoring stations around the world, most overseen by the Comprehensive Nuclear-Test-Ban Treaty Organization, have been on alert since the first seismic waves were detected Wednesday morning, sniffing the air for radioactive material that can reveal so much about nuclear weapons tests. The Japanese media has reported that Tokyo mobilized its own aircraft over the Sea of Japan to collect atmospheric data, but that no radioactive material had been detected so far. While radioactive gases almost certainly escaped from the underground test site, the radioactive dust that scientists normally need to distinguish a hydrogen bomb explosion from less powerful atomic blasts — like North Korea's three previous nuclear tests — may not reach the atmosphere. Since hydrogen bombs detonate in two distinct stages, scientists use a series of complex measurements of the radioactive dust, including calculating the remaining nuclear fuel from the primary explosion, to distinguish hydrogen bombs from atomic bombs. With gases, researchers measure the amounts of certain radioactive materials, particularly various forms of xenon, to determine such things as whether the bomb was fueled by plutonium or highly enriched uranium.