Question

Define nuclear fission, nuclear chain reaction, and critical mass.

Short answer

Nuclear fission is a reaction where an atom's nucleus splits into smaller nuclei, releasing energy and free neutrons. A nuclear chain reaction is when these free neutrons trigger further fission reactions. Critical mass refers to the minimum quantity of fissile material required to sustain a nuclear chain reaction.

Step-by-step solution

Defining Nuclear Fission

Nuclear fission is a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into two or more smaller, lighter nuclei. It usually releases a significant amount of energy in the form of gamma photons and free neutrons.

Defining Nuclear Chain Reaction

A nuclear chain reaction occurs when the products of a nuclear fission reaction trigger further reactions. In nuclear physics, this is typically done by free neutrons from a fission event causing an additional fission, which in turn releases more neutrons than can cause more fissions.

Defining Critical Mass

Critical mass is the minimum amount of fissile material needed to maintain a nuclear chain reaction. The exact mass depends on several factors, including the type of fissile material, its shape and density, and the degree to which neutrons are reflected back into the material.