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Physics 8463 - 4.4 Atomic structure

4.4.4 Nuclear fission and fusion

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4.4.4.1 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 (you learn differently concerning this in further study - but in the exam tell them what they have put in the syllabus!), 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.

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

This topic has been seriously depleted from previous years - many old examination papers will ask about things you do not need to recall any more. So don't let them scare you

4.4.4.2 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.