If anyone can help me with this question I'd be greatly appreciative.... Here's what I think I understand: Nuclear fission is the breaking of an atomic core of an atom. Like with U-235. It absorbs a slow moving neutron which yields the unstable U-236. Because of the instability the atomic core fissions. Yielding Kr and some other element (can't remember which one) along with 2 neutrons (or more). These 2 neutrons hit other U-235 atoms, amplifying the nuclear fission with each generation of more neutrons. So, where does the stray neutron come from? I kind of understand radioactive decay.... but I haven't read any mention of a neutron coming out. Radioactive decay releases alpha particles, beta particles and gamma rays. Alpha particles are Helium atoms without the electrons, so they are positive and would be repelled from the atomic core of U-236. Also, they have alot of mass, travel slowly and have short range. Beta particles are electrons, they move faster, have a longer range but would get repelled from the electron cloud (I think), and wouldn't be able to make an atomic core unstable. Gamma rays aren't particles but are waves and have no mass. So they wouldn't be able to make an atomic core unstable. What am I missing!?!?!?!?!?!? Everywhere I read the article just assumes this neutron floating around approaching a some heavy elements atomic core. But where does this neutron come from? Is it a 4 type of radioactive decay? Along with alpha, beta and gamma.... a neutron can get shot out? Thanks for any help.