It wouldn't have detonated. The worst that would have happened... is exactly what did happen. Lots of radiation release and the death of one nuclear scientist that should have been more careful (he died of radiation sickness a few days later).

Yea, after reading the article fully I wish I could edit my comment a bit. It isn't really amazing when 3 people died because of it (2 other scientists apparently later died as well).

Or accidently dropping a tungsten carbide brick on the plutonium bomb core, for that matter...(http://en.wikipedia.org/wiki/Harry_K._Daghlian,_Jr.) That picture fascinates me. It's like a deadly game of Jenga.

> I have had a lot of oh shit moments in my days, but none gets close to dropping the plutonium onto the uranium and nearly detonating a nuclear payload.

Not possible for a plutonium device, and this is why the implosion method was so technically challenging. The plutonium must be transitioned from subcritical to supercritical very, very fast to achieve any significant nuclear energy release. In the final design, shaped plastic explosives, chosen for their very high velocities, were used to compress the plutonium from all directions simultaneously, very fast. Then, after the compression phase is complete, a carefully timed burst of neutrons triggers the nuclear fission event.