7.3.1Radioactivity and Particles
Nuclear Energy — Edexcel International GCSE Science Double Award 4SD0 - Physics Revision Notes & Topical Questions
10 min read 14 parts Lesson 14 of 18
Part 1 of 7Energy stored in the nucleus
Nuclei are held together by the strong nuclear force, which acts between protons and neutrons over very short distances and is much stronger than the electrostatic repulsion between protons.
- and ends up mainly as thermal energy in the surrounding material.
Chemical reactions such as burning rearrange the outer electrons of atoms. Nuclear reactions rearrange the particles inside the nucleus, and the energy changes involved are roughly a million times larger per atom.
Part 2 of 7Two ways of releasing nuclear energy
Both reactions give out energy because the products are in a lower-energy, more stable arrangement than the starting nuclei.
Part 3 of 7Mass and energy (extension)
If you measure the masses very accurately, the total mass of the products of fission or fusion is slightly less than the mass of the starting particles. The "missing" mass has been transferred to energy. Einstein’s equation links them:
E = mc2
where E is the energy released in joules (J), m is the mass lost in kilograms (kg) and c is the speed of light, 3.0 × 108 m s−1.
Part 4 of 7Comparing nuclear and chemical fuels
The energy produced per kilogram of fuel shows the difference clearly. Burning coal releases around 3 × 107 J per kilogram. Complete fission of uranium-235 releases of the order of 8 × 1013 J per kilogram, millions of times more. Fusion of hydrogen isotopes releases several times more again per kilogram than fission.
This explains why a nuclear power station needs only a few tonnes of fuel in a year, while a coal-fired station of the same power needs millions of tonnes. It also explains why the Sun, which fuses hydrogen into helium, can shine steadily for billions of years.
Part 5 of 7Advantages and drawbacks of nuclear power
Linkthe next lessons explain how fission happens, how a reactor controls it, and how fusion can occur.
Part 6 of 7Nuclear energy in context
It helps to compare the scale of energies.
Exam questions often ask for a comparison. Make clear statements: the energy per kilogram is far greater, the amount of fuel needed is far smaller, and there is no carbon dioxide emitted during operation, but radioactive waste is produced and must be stored for a long time. Link the idea to power stations (fission) and to the Sun (fusion).
Part 7 of 7Worked examples
In a nuclear reaction the total mass decreases by 3.0 × 10−28 kg. Calculate the energy released. (c = 3.0 × 108 m s−1)
E = mc2 = 3.0 × 10−28 × (3.0 × 108)2
= 3.0 × 10−28 × 9.0 × 1016 = 2.7 × 10−11 J.
This seems small, but it comes from a single reaction; a kilogram of fuel contains about 1024 or more nuclei.
A power station burns coal that releases 3.0 × 107 J per kg. How many kilograms of coal give the same energy as 1.0 kg of uranium-235 that releases 8.0 × 1013 J?
Mass of coal = 8.0 × 1013 ÷ 3.0 × 107
= 2.7 × 106 kg, i.e. about 2.7 million kg (2700 tonnes).
A reaction releases 5.4 × 10−12 J of energy. What mass is converted to energy? (c = 3.0 × 108 m s−1)
m = E ÷ c2 = 5.4 × 10−12 ÷ 9.0 × 1016
= 6.0 × 10−29 kg.
Key terms
| Term | Meaning |
|---|---|
| Strong nuclear force | Attractive force that holds protons and neutrons together in the nucleus. |
| Nuclear fission | Splitting of a large nucleus into two smaller nuclei, releasing energy. |
| Nuclear fusion | Joining of two light nuclei into a heavier nucleus, releasing energy. |
| E = mc2 | Equation linking energy released to the mass converted and the speed of light. |
| Radioactive waste | Material from nuclear processes that remains radioactive. |
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