Terrorists are not technically advanced enough to produce a detonator or the timing mechanism necessary for supercritical mass.
You claim that all that is necessary for achieving supercritical mass, is to cast a convex and concave sphere from the same die, and there you have it! All of which can be achieved from inside any average garage. In other words, there just ain't nothing to it!
The electricly charged hexaflouride suspention medium you speak of is also difficult to envision. Just what would be it's purpose? Since it is required to drive the isotope's core into the outer sphere, how would that work?
In the case of "FAT MAN", R. Oppenheimer and his team used a U-238 outer shell and a plutonium core, which allowed them to use a 22 pound core instead of the original 35 pound core as first therorized.
"LITTLE BOY" was constructed solely from U-238 and it required 100 Kg (or 220 pounds) of U-238. This material was so much more advanced than simple "Enriched Uranium" all of which is extremely dangerous to work with. Anyone directly exposed to this material would only last a few hours afterwards. But really, easily accomplished in any ones garage?
Actually, "Fat Man" detonated with a yield of around 20 kilotons.
"LITTLE BOY" was constructed solely from U-238 and it required 100 Kg (or 220 pounds) of U-238.
"Little Boy" used Uranium 235 as its nuclear fuel. We had to use almost every bit of U-235 available to create just one bomb. Plutonium was easier to produce than U-235 was to separate so that is why Plutonium was used in both "Trinity" and "Fat Man". It would have been months before another Uranium gun weapon would have been ready where as there was enough Plutonium for three bombs and plenty more on the way.
I wasn't talking about thermonuclear bombs. Thermonuclear bombs are fusion bombs. I was talking about fission bombs.
I'm sorry, but you're wrong. Little Boy was made of 110 pounds (50 kgs) of U-235. You're off on both your weights and Uranium types.