how trigger mechanism works in nuclear weapons?

Answer 1

There are different types, but here's one example: A small conventional explosive is used to force together 2 chunks of sub-critical uranium 235. The compression causes fission in some of the uranium atoms (which are unstable), and they release neutrons that strike other uranium atoms, causing them to split apart as well -- there is a runaway chain reaction which releases MASSIVE amounts of energy. This is the nuclear explosion.

Answer 2

Nature_boy answered correctly for a uranium bomb, but plutonium requires a more elaborate scheme.

In a plutonium bomb the plutonium "pit" must be compressed to critical mass, so it is surrounded by a sphere of conventional explosives all detonated at exactly the same time. The explosion provides the compression required. Obviously, if the detonation is not completely symmetrical, the bomb will have greatly reduced efficiency or may not even detonate (as a fission detonation)

And as for fusion weapons, I think they work mostly like a plutonium fission weapon, but I don't know how the hydrogen fuel is incorporated

Answer 3

I'm not sure about nuclear weapons, but in nuclear reactors they fire a neutron at the uranium or plutonium in the reactor and when it contacts one of the atoms it rips it apart and releases all the neutrons which then continue on to impact more atoms which then release more neutrons which hit more atoms, etc., etc. This process is controlled inside nuclear reactors so that the uranium or plutonium doesn't explode but is allowed to cascade out of control with nuclear weapons which is how they get the massive explosion.

Answer 4

I understood that they used a small particle accelerator to bombard a nuclear particle, ripping it apart, releasing a lot of energy which starts a chain reaction of particles getting ripped apart until all the fuel is spent.