The North Korean news agency statement about the purported nuclear test made much of the fact that there was no radiation release. Reported measures of the blast effect ranged between 3.6-4.2 on the Richter scale. A one kiloton weapon produces an effect that measures about 4.0, thus what took place was a detonation of something somewhat more or less than 1000 tons of TNT. But if there are no radiation signals, do we really know it was a nuclear test? It is possible that they just blew up a large conventional munition. For decades the US has conducted High Explosive Simulation Technique (HEST) tests using conventional munitions to simulate low-yield nuclear blasts, up to the 4 kiloton level. The only way to know for certain that a given blast is nuclear is by radiation. Thus when Pyongyang makes a big deal about how there was no radiation released, one must wonder. Perhaps the radionuclide monitoring stations in the region can tell us something. Of course it is possible that a test could be conducted with absolutely no radiation release. But if there is none, there is also no definitive proof North Korea conducted a nuclear test.