Say you want to make a fission reaction, how exactly do you launch a neutron toward this atom to split it? Which device do you use?
I am not sure if you launch another atom or just a neutron.
Trial and error.
Keep bombarding the nucleus until it’s hit by the right neutron at the right speed to cause a reaction.
For more details, look up the answer by r/popsickle_in_one
In a fission reaction, a reactor has a neutron flux that’s between 10^10 and 10^13 neutrons per cm^2 passing through the cord every second. That’s an absolutely massive amount of neutrons.
The neutrons come from the fission reaction. Splitting an atom makes 1-7 neutrons (2.4 is the average) and in a steady state reactor those 2.4 neutrons bounce around and slow down and you lose 1.4 of them and the remaining 1 neutron causes another fission.
We are dealing with massive numbers of fissions and atoms though. Millions of billions per second in the entire core.
When you are shut down, the neutrons come from the nuclear waste products breaking down. If you have a brand new core or if the core was shutdown for years you usually will insert a neutron source like CF 252 which provides some starter neutrons to allow you to better control and monitor the reaction and essentially jump start the core.
In a nuclear reactor there are lots and lots of neutrons pinging about. They’re being fired off by the radioactive decay of the fuel in all directions. To start a nuclear reactor, neutron sources are used. These are radioactive elements that undergo spontaneous fission to create neutrons, which are used to start the reactor.
Using control rods to moderate the speed of the neutrons helps them hit other uranium atoms. This splits the atom, gives off energy (which we use to make electricity) and sends off more neutrons in a random direction. Some of those neutrons go on to split more uranium atoms and the reaction continues.
There are also ‘neutron guns’ or modulated neutron initiators. This is the trigger for a fission bomb. Usually some combination of radioactive elements that create neutrons when they react. In a nuclear bomb, there is a small explosion that smashes the trigger elements together. This creates a massive burst of neutrons, which then smash into the supercritical core of the weapon, accelerating the nuclear reaction.
The trick is to get the timing right so the neutrons hit the core at the right time. Too early and the you get a low yield. Too late and the core is already falling apart and you don’t get a big explosion.