Fission, Fusion, and Nuclear Decay
Introduced| English | Meaning |
|---|---|
| nuclear fission/ˈnjuːklɪə ˈfɪʃn/ | The splitting of a heavy atomic nucleus into smaller nuclei, usually releasing energy and neutrons. |
| nuclear fusion/ˈnjuːklɪə ˈfjuːʒn/ | The joining of light atomic nuclei to form a heavier nucleus, releasing energy. |
A pinch of matter, an ocean of energy
- The Sun turns four million tonnes of its matter into pure energy every second.
- A nuclear reactor powers a city from a few kilograms of fuel.
- The secret is mass turning into energy, through Einstein's $E = mc^2$.
- Because $c^2$ is enormous, a tiny mass releases a colossal amount of energy.
Mass becomes energy
- Einstein's relation $E = mc^2$ says mass and energy are two forms of the same thing.
- In a nuclear reaction, a little mass disappears and reappears as a burst of energy.
- Because $c^2 \approx 9\times10^{16}$, even a gram of mass would give a huge energy.
- Nuclear reactions release millions of times more energy per atom than chemical ones.
Which equation relates mass and energy?
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Einstein's $E = mc^2$ links mass and energy.
Why do nuclear reactions release so much more energy than chemical ones?
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Converting even a tiny mass gives huge energy because $c^2$ is so large.
Fission: splitting big nuclei
- Nuclear fission 核裂变 splits a large, heavy nucleus (like uranium) into smaller pieces.
- The fragments have slightly less total mass; the lost mass becomes energy.
- Each split also releases neutrons that can split more nuclei — a chain reaction.
- Fission powers nuclear reactors and atomic bombs.
Nuclear fission is the:
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Fission splits a large, heavy nucleus into smaller pieces.
Fusion: joining small nuclei
- Nuclear fusion 核聚变 joins small, light nuclei (like hydrogen) into a bigger one.
- Again a little mass is lost and released as energy — even more per kilogram than fission.
- Fusion powers the Sun and the stars, welding hydrogen into helium.
- It needs extreme heat and pressure, which is why fusion power on Earth is so hard.
Fission, fusion or decay?
Sort each nuclear process.
Nuclear fusion powers the ____ and the stars.
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The Sun fuses hydrogen into helium, releasing its energy.
Select all true statements about nuclear reactions.
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Fission splits, fusion joins, and both release energy from lost mass. Fusion releases energy too.
Both fission (splitting) and fusion (joining) release energy, because in each the products have slightly less mass than the starting nuclei. The "lost" mass isn't destroyed — it becomes energy via $E = mc^2$. Don't assume only splitting releases energy; fusion of light nuclei releases even more.
Fission releases energy, but fusion always absorbs energy.
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False. For light nuclei, fusion also releases energy: in both processes the products have slightly less mass, and the lost mass becomes energy via $E = mc^2$.
The Sun fuses hydrogen into helium. Where does its enormous energy come from?
- The helium nucleus has slightly less mass than the hydrogen that made it.
- That tiny lost mass becomes energy via $E = mc^2$ — and with $c^2$ so large, it is immense.
Nuclear reactions convert mass into energy via $E = mc^2$, releasing millions of times more energy per atom than chemical reactions. Fission splits heavy nuclei (reactors, bombs); fusion joins light nuclei (the Sun). In both, the products have slightly less mass, and that mass becomes energy.
Write from an energy of 9 times 10 to the 13 joules
- A nuclear change loses 0.001 kg of mass.
- Take c as 3 times 10 to the 8 metres per second. Find the energy released.
A nuclear reaction converts 0.001 kg of mass into energy. Take the speed of light as 3 times 10 to the 8 metres per second. How much energy is released, in joules?
0.001 times 9 times 10 to the 16 is 9 times 10 to the 13.
How much energy does the lost mass release?
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Mass times c squared is 9 times 10 to the 13 joules.