My theory on why North Korea nuke tests have been low yield duds.
I've mentioned this in another thread related to North Korea's nuclear tests, but thought I would invite discussion in a thread of its own. Disclaimer: Not a nuclear scientist, not a weapons designer, do not play one on TV, did not stay at "Holiday Inn Express" last night. This is speculation based on what I've read about the tests in traditional media sources.
In the early days of the Manhattan Project, America's nuclear scientists had hopes for creating a simple plutonium based weapon similar to the "Gun" design that was used in the uranium based "Little Boy" weapon dropped on Hiroshima. The design, known as "Thin Man" would work by firing a sub-critical mass plutonium into another sub-critical mass plutonium target. The device had the advantage of being comparatively simple to construct and highly reliable, but not very efficient.
But, it turned out that the design had a fatal flaw, in order to prevent pre-detonation , the two masses had to be brought together at tremendous speeds - much higher than a uranium bomb required. The gun barrel required to fire the plutonium to speeds where pre-detonation would be less likely would require a gun barrel too long for any existing or planned bomber. The designers turned to a much more difficult implosion design to create a deliverable plutonium fission device.
Which leads me to North Korea's three underground nuclear tests. Creating a plutonium implosion device is still a very difficult engineering challenge - requiring great precision, substantial costs, and difficult to obtain tooling. But, creating a "Thin Man" device is rather simple - it just takes construction of a rather large gun barrel. What you get is a very dirty, inefficient, low yield nuclear device - which accurately describes the three North Korean tests.
In terms of weapons design, Thin Man is a dead end. It will not lead to a warhead that could ever be carried on a missile, aircraft of artillery shell. But since nobody outside of North Korea seems to any solid data about the design of the devices they have tested, it can be an effective political bluff. It would be cheap to develop and have a high likelihood of creating a low yield nuclear detonation. North Korea has attempted sell the idea that they are creating "Highly Miniaturized" devices to explain the low yields, but most weapons experts seem to think that this is unlikely given the level of technology that North Korea possesses and consider it more likely that the tests were fizzles in which only a small portion of the plutonium underwent fission. An imperfect implosion would do that - or a Thin Man.
It might be possible for North Korea to deliver a low yield Thin Man device - in the back of a large truck, shipping container, railroad car or in the hold of a ship. Despite the low yield, because it is a very "Dirty" device, it could spread radioactive contamination over a large area. But fears of North Korea mounting one of these things on one of their crude ballistic missiles? Not likely.
= new reply since forum marked as read
