How to Slow Down a Neutron in a Nucleus

The problem is that when the neutrons fly out, they have a lot of energy. And even if you pack your uranium pretty tightly, the neutrons that come out are moving too quickly. So what you need is something to slow down those neutrons to just the right speed so they have a high enough chance of hitting a nucleus and triggering another reaction. It's about like the probability of hitting another atom, right? Like a if the hairs from the camel are flyi aa too fast, they'll just miss all the other camels. But if it's groing slow, then there's a bigger chance that, you know, a camel will walk into the path of one