How do you determine if a reaction is a fission or fusion reaction?
Fission splits an atom. Fusion Combines two atoms.
Nuclear fission starts with big atoms. That is, atoms with more protons and neutrons than
Generally fission is initiated by a neutron hitting the nucleus of one of these big atoms, causing it to break up into two atoms of roughly half the size of the original atom and one or more neutrons (which then go on to initiate other fission reactions).
Fusion starts with small atoms. Think the first two periods of the periodic table. These atoms can be mashed together using high temperatures and, in stars, high pressure, to make new, heavier elements.