P2.6.1 - AQA GCSE Physics Unit 2

P2.6.1	Nuclear fission
	a) There are two fissionable substances in common use in nuclear reactors: uranium-235 and plutonium-239.	The majority of nuclear reactors use uranium-235.
	b) Nuclear fission is the splitting of an atomic nucleus.
	c) For fission to occur the uranium-235 or plutonium-239 nucleus must first absorb a neutron.
	d) The nucleus undergoing fission splits into two smaller nuclei and two or three neutrons and energy is released.
	e) The neutrons may go on to start a chain reaction.	Candidates should be able to sketch or complete a labelled diagram to illustrate how a chain reaction may occur.