Nuclear fusion• Nuclear fusion occurs when

two small nuclei fuse together and release large amounts of energy.

• The energy released is due to a slight decrease in mass of the fused particles compared to the sum of their original masses.

Copy and label the diagram

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Hydrogen and Helium make up around 98% of all mass in the entire universe.

Why do some nuclei undergo fusion and some fission? (Not on specification)You may remember seeing this diagram towards the beginning of the topic. In actual fact, all nuclei can undergo either fusion or fission, we are simply looking at cases where either process releases energy rather than absorbs it. E.g. fusion of iron (Fe) takes more energy than it releases as the binding energy per nucleon (y axis) starts to fall. Equally, the fission of Carbon (C) to Lithium (Li) would also take more energy than it releases.

Creating nuclear fusion• To cause a nuclear fusion

reaction, two nuclei have to be forced together with enough force to overcome the electrostatic repulsion of their positive protons.

We will learn more about this in the next topic.

Nuclear fusion in the Sun• The centre of the Sun has a very high temperature and

an extremely high pressure due to the large gravitational forces present.

• The combination of temperature and pressure is sufficient to force nuclei together and maintain a fusion reaction in the star.

High pressure forces the nuclei closer together and high temperature causes them to move faster, both of which increase the chances they will collide and fuse.

Nuclear fusion on Earth•On Earth, we are currently unable to simulate

pressures anywhere near as high as those in the Sun. Instead, we make up for this by using much higher temperatures to cause fusion reactions.

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Benefits of nuclear fusion•Nuclear fusion reactors could

potentially produce much more energy than fission reactors. Also, the waste product of fusion is helium which is not radioactive so does not have to be contained and stored.

• Fusion produces a lot more energy than fission because of the much bigger increase in binding energy per nucleon (y axis) in each process (shown by the two blue arrows).

Issues with nuclear fusion• The reactor used to contain the fusion reaction does

become slightly radioactive and must be decommissioned safely. The main issue with fusion currently however is getting more energy out than you put in (e.g. generating the high temperatures in the reactor).

Even in the last few years, scientists are getting closer and closer to ‘breaking even’ with energy

and new research laboratories are being built around the world (see article link on cover sheet)

Work to submit• First please complete the worksheet SP6m.5 Q1-6.

• You are then free to do the test whenever you are ready, as long as it is submitted by the end of Friday 8th. I would suggest spending around 30-60m making a mind map or revision cards of the topic or completing practice exam questions beforehand. https://www.physicsandmathstutor.com/physics-revision/gcse-edexcel/radioactivity/