Sure you can speed it up: get something else to decay neutrons, protons or alpha particles, on to it.
An atomic bomb is when you convince a lot of Uranium-235 or Plutonium to decay all at once in an uncontrolled way.
A nuclear reactor is what happens when you convince material to decay at a controllable rate.
It's way more complex than that but you can look up the rest, e.g. "Nuclear chain reaction".
Where I think you're going with this is
https://physics.stackexchange.com/questions/594598/destroyin...
tl;dr: it's more trouble than it's worth, since you need radioactive materials as the neutrons sources, and stray neutrons tend to bump into other matter and cause yet more radioactive waste.