North Korea says it tested a nuclear weapon.  Western governments say North Korea tested a nuclear weapon.  Seismic sensors produced data that show that North Korea tested a nuclear weapon.  And that has the spies and scientists wondering..
Where’s the radiation?

U.S. and allied spy agencies have yet to detect the telltale nuclear particles following the 12 February underground explosion in far northeastern North Korea.

And that’s a major hole in what the major western powers know about Pyongyang’s nuclear program.  North Korea’s official news agency said it had used “a miniaturized and lighter nuclear device with greater explosive force than previously (and which) did not pose any negative impact on the surrounding ecological environment.”

Another critical question surrounds what type of fissionable material was used in the latest blast.  In the previous two tests, the scientists could determine that the North Koreans used plutonium.  Not so much this time.