Nuclear fission
The process of splitting a The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei. is called The splitting of a large nucleus to produce two smaller ones. and is used in nuclear power reactors.
The absorption of slow Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0. can induce fission in particular nuclei, which are referred to as the fissile nuclei. Neutrons emitted from such fission can lead to a sustainable A nuclear chain reaction occurs when a neutron splits a nucleus, releasing more neutrons, which in turn go on to split even more nuclei.. If neutrons are moving too fast, fission will not occur.
Uranium or plutonium Atoms of an element with the same number of protons and electrons but different numbers of neutrons. are normally used as the fuel in nuclear reactors. Their atoms have relatively large nuclei that are easy to split, especially when hit by neutrons. The nuclear symbol for a neutron is \(_{0}^{1}\textrm{n}\).
When a uranium-235 or plutonium-239 nucleus is hit by a neutron, \(_{0}^{1}\textrm{n}\) the following happens:
- the nucleus splits into two smaller nuclei known as daughter nuclei, which are When unstable atoms give off particles that can be harmful to humans.
- two or three more neutrons are released
- some energy is released in the form of kinetic energy of the particles produced
The equation can be written as
\(_{92}^{235}\textrm{U}+_{0}^{1}\textrm{n}\rightarrow_{56}^{144}\textrm{Ba}+_{36}^{89}\textrm{Kr}+{3}_{0}^{1}\textrm{n}+ {\text{energy}}\)
Chain reaction
The additional neutrons released may also hit other uranium or plutonium nuclei and cause them to split. Even more neutrons are then released, which in turn can split more nuclei.
This is called a chain reaction.
The chain reaction in nuclear reactors is controlled to stop it moving too quickly.
Many of the fission products are also radioactive and they decay with a large range of half-lives. Technetium-99 has a The time it takes for the number of nuclei of a radioactive isotope in a sample to halve. Also defined as the time it takes for the count rate from a sample containing a radioactive isotope to fall to half its starting level. of 211,100 years, but other fission products may have half-lives of about 5 years.