so, i get that atoms can be split by colliding with neutrons, but how does one get a singular neutron?
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By grabbing radioactive stuff that is decaying and emitting particles in the process. Take your pick: electrons, neutrons, positrons, helium.. wathever you need.
You don’t need to “get” a singular neutron, you just need to bring that stuff close enough to your fissile material so that the neutrons hit your atoms and the chain reaction starts.
This depends on your purpose. In a nuclear bomb or reactor, the neutrons come from other nuclei splitting. The first neutron either comes from a random decay event or from a specialized neutron source.
A few systems to create neutron radiation on-demand exist, too. Nuclear weapons use something which is radioactive in some other kind of radiation, and suddenly combine it with a different element, which is struck by the radiation to free neutrons.
Or you can just perform nuclear fusion. Easy. Not easy to generate electricity from, but easy to do.
You don’t “get” a single neutron. You have some radioactive element that’s emitting neutrons and you place a bit of it it next to a bit of the radioactive element you want to split, and the neutrons will have some probability of hitting the atoms and splitting the. You can alter that probability by changing the shape, size, and distance, of the 2 materials, and also what materials they’re in (i.e., are they in air, water…etc).
There are some nuclear reactions that produce neutrons. The classic one is an alpha particle colliding with a beryllium atom, which then ejects a neutron. So to make a neutron source (or “gun”), you need to put a strong alpha emitter (like radon or polonium or radium) next to beryllium. This will generate neutrons in random directions. To make it a “gun” you could put the whole thing in a box made of something that absorbs neutrons, and then cut a little hole in it, so that only the neutrons going in the direction of the hole would get out.
In the first atomic bomb, there was a little capsule in the center of the bomb that was made out of beryllium, polonium, and a little bit of gold foil separating the two of them. Around this was some more beryllium, with little spikes cut in it, [like this](https://blog.nuclearsecrecy.com/wp-content/uploads/2015/05/Urchin.png). Prior to detonation, the gold absorbed the alpha particles from the polonium and prevented them from reaching the beryllium. When the bomb was set off, it crushed the capsule, the spikes broke the foil, and the beryllium and polonium got mixed together. This created around 100 neutrons that were used to “jump start” the bomb’s chain reaction. There likely would have been neutrons already available, even if the capsule wasn’t there, because plutonium (the nuclear fuel) has some level of “spontaneous fission” that means neutrons are always present in it. But they wanted to make sure there was a “blast” of neutrons at just the right moment, to make sure the reaction got off to a good start.
A neutron source. We have identified a few materials that we can fire alpha particles at, causing it to eject neutrons at high speeds. We then use these neutrons to do what we wish.
Alpha particles are easy enough to obtain as a very common mode of radioactive decay, and they are a charged particle, so we can accelerate them to any desired speed in a particle accelerator.
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