[Music] hi and welcome back to three times less than cold UK by the end of this video you should be able to describe what learn by nuclear fission and a chain reaction you should then be able to describe how nuclear fission may be controlled or uncontrolled and finally you should be able to describe what happened the nuclear fusion and all of this is for triple physics students only so we're going to start by looking at nuclear fission the first Kyogre you need to understand is that in some elements the nucleus is large in unstable and
then examples of these are uranium and plutonium now I should point out that this only applies to certain isotopes of these elements but for the exam you're not required to name those isotopes in nuclear fission the nucleus of these elements split now this can happen spontaneously in other words by itself but that's quite rare normally for fishing to take place the nucleus first has to absorb a neutron so here I'm showing you a number of uranium nuclei when uranium nucleus absorbs a neutron this triggers a nucleus to undergo fission another word split like this when
the nucleus splits it forms two smaller nuclei roughly equal in size scientists call these the daughter nuclei it also emits two or three neutrons plus gamma radiation energy is also released during the fission reaction so example all of the fission products have got kinetic energy now the really important part about this process is what happens to the neutrons emitted you incision the neutron can now be absorbed by more uranium nuclei on trigger position again like this and again when the nuclear undergo fission they emit two or three more neutrons each and these can then go
on to trigger fission themselves so in a very short time a huge number of uranium nuclei have undergone fission and an enormous amount of energy has been released scientists call it a chain reaction and it's really important that you learn that now scientists can control the fission chain reaction and use the energy released to generate electricity we find this in nuclear reactors however the explosion in a nuclear weapon is caused by an uncontrolled station chain reaction okay so we've seen what happens a nuclear fission but what about nuclear fusion this is a totally different process
in nuclear fusion two light nuclei for example hydrogen or join to form a heavier nucleus some of the mass of the nuclei can be converted into energy and that releases radiation now nuclear fusion is the process that releases energy in stars such as the Sun it's important to understand that nuclear fusion is not a chain reaction we only use that expression when talking about nuclear fission remember that you'll find plenty of questions on nuclear fission and on nuclear fusion in my vision workbook and you can get that by clicking on the link above ok so
hopefully now you should be able to describe what's meant by nuclear fission and a chain reaction you should then be able to describe how nuclear fission may be controlled or uncontrolled and finally you should be able to describe what happens in nuclear fusion [Music]
