A nuclear chain reaction takes place roughly over a single microsecond. To travel the ~11 inches of a bomb, in ideal circumstances, a high explosive needs roughly 200 microseconds. It is not impossible that the exact right stuff could happen to trigger the bomb, but it is extremely unlikely - it took the smartest minds in america working together for 3 years to figure out the exact precise timing to prevent a nuclear fizzle and achieve a true atomic explosion. It is, contrary to pop culture, near-impossible to pull off by dumb luck. Mostly you'll just make a radioactive mess.