[SpaceBar]

Color me skeptical. Ivy-Mike would have weighed in at 8.6-8.7 in magnitude if detonated underground. And that was our first crack at it sixty years ago.

[TigerLikesRooster]

There has been suspicions hanging over N. Korea's nuclear test. Bomb's yield has been too low. Some experts speculated that they went straight to miniaturized nuke bypassing the intermediate steps where they have to first demonstrate that a simpler bomb works. Such a bomb has a higher yield. Lower yield miniature nuke is harder to make, according to them.

[familyop]

See the facility described and illustrated in the following from 2006, and you'll see how N. Korea's claim is likely correct. Thanks to TigerLikesRooster.

S. Korean Lawmaker, "Russia might have given N. Korea know-how of miniature nukes"
http://www.freerepublic.com/focus/f-news/1717327/posts