What is nuclear fission?

Nuclear fission is the splitting of a massive nucleus into photons in the form of gamma rays, free neutrons, and other subatomic particles. In a typical nuclear reaction involving ²³⁵U and a neutron:

²³⁵ ₉₂U + n = ²³⁶ ₉₂U followed by ²³⁶ ₉₂U = ¹⁴⁴ ₅₆Ba + ⁸⁹ ₃₆Kr + 3n + 177 MeV

For a fission reaction, two conditions need to be satisfied:

1. Critical mass of the substance (the minimum amount of mass is required for fission to be self-sustaining).

2. A relatively slow neutron is required to initiate the process.