Well, I'll be honest my physics is not good. But I really wonder about radiation and other physical stuff.
When I search about it I see three types of ionizing radiation: Alpha, Beta and Gamma. But when I search about nuclear weapons I see that they work by launching a neutron to a u235. So I wonder how is this neutron launched? I know that fission occurs 2 or 3 neutrons. But you need a neutron to start fission, right?