# Summarizing Fission

## Fission Summary

• Nuclear fission is a reaction in which a nucleus is split.
• Fission releases energy when heavy nuclei are split into medium-mass nuclei.
• Self-sustained fission is possible, because neutron-induced fission also produces neutrons that can induce other fissions, $$n+{}^{A}X\to {\text{FF}}_{1}+{\text{FF}}_{2}+\text{xn}$$, where $${\text{FF}}_{1}$$ and $${\text{FF}}_{2}$$ are the two daughter nuclei, or fission fragments, and x is the number of neutrons produced.
• A minimum mass, called the critical mass, should be present to achieve criticality.
• More than a critical mass can produce supercriticality.
• The production of new or different isotopes (especially $${}^{\text{239}}\text{Pu}$$ ) by nuclear transformation is called breeding, and reactors designed for this purpose are called breeder reactors.

## Glossary

### breeder reactors

reactors that are designed specifically to make plutonium

### breeding

reaction process that produces 239Pu

### criticality

condition in which a chain reaction easily becomes self-sustaining

### critical mass

minimum amount necessary for self-sustained fission of a given nuclide

### fission fragments

a daughter nuclei

### liquid drop model

a model of nucleus (only to understand some of its features) in which nucleons in a nucleus act like atoms in a drop

### nuclear fission

reaction in which a nucleus splits

### neutron-induced fission

fission that is initiated after the absorption of neutron

### supercriticality

an exponential increase in fissions