Nuclear fission

Nuclear fission is the splitting of a large and unstable nucleus (eg uranium or plutonium).

Spontaneous fission is rare. Usually, for fission to occur the unstable nucleus must first absorb a neutron.

The nucleus undergoing fission splits into two smaller nuclei, roughly equal in size, and emits two or three neutrons plus gamma rays. Energy is released by the fission reaction.

All of the fission products have kinetic energy.

The neutrons may go on to start a chain reaction.

The chain reaction is controlled in a nuclear reactor to control the energy released. The explosion caused by a nuclear weapon is caused by an uncontrolled chain reaction.

Students should be able to draw/interpret diagrams representing nuclear fission and how a chain reaction may occur.

Nuclear fusion

Nuclear fusion is the joining of two light nuclei to form a heavier nucleus. In this process some of the mass may be converted into the energy of radiation.