Nuclear fusion is the process in which light atomic nuclei combine to form heavier nuclei, releasing a large amount of energy. It powers the Sun and most stars, where hydrogen nuclei fuse into helium under extreme temperature and pressure. Fusion matters because it explains stellar energy, element formation, and the possibility of a powerful low-carbon energy source on Earth.
In chemistry and physics, it connects atomic structure, nuclear forces, mass-energy conversion, and plasma behavior.
Key Facts
- Fusion combines light nuclei, such as hydrogen isotopes, into heavier nuclei, such as helium.
- Mass-energy conversion is given by E = mc^2, where a small lost mass becomes a large amount of energy.
- In the proton-proton chain, the net reaction is 4 1H -> 4He + 2e+ + 2νe + energy.
- Nuclei must get close enough for the strong nuclear force to overcome electric repulsion between protons.
- Fusion requires plasma, an ionized gas of free electrons and nuclei, at temperatures of millions of kelvin.
- Magnetic confinement uses fields to guide charged particles because F = qvB for motion perpendicular to a magnetic field.
Vocabulary
- Nuclear fusion
- Nuclear fusion is a reaction in which two or more light nuclei join to form a heavier nucleus and release energy.
- Plasma
- Plasma is a hot ionized state of matter containing free electrons and charged nuclei that respond strongly to electric and magnetic fields.
- Proton-proton chain
- The proton-proton chain is the main sequence of fusion reactions that converts hydrogen into helium in Sun-like stars.
- Neutrino
- A neutrino is a nearly massless neutral particle produced in some nuclear reactions that rarely interacts with matter.
- Confinement
- Confinement is the process of keeping extremely hot plasma dense and stable long enough for fusion reactions to occur.
Common Mistakes to Avoid
- Confusing fusion with fission, because fusion joins light nuclei while fission splits heavy nuclei.
- Thinking fusion releases energy because atoms burn chemically, because fusion changes nuclei and releases energy from mass difference, not electron rearrangement.
- Ignoring electric repulsion between protons, because positively charged nuclei repel and must have very high temperature or quantum tunneling to approach closely.
- Assuming any hot gas will fuse, because useful fusion requires high temperature, enough density, and sufficient confinement time together.
Practice Questions
- 1 In a fusion reaction, 3.0 x 10^-29 kg of mass is converted to energy. Use E = mc^2 with c = 3.0 x 10^8 m/s to calculate the energy released.
- 2 If one fusion event releases 4.0 x 10^-12 J, how many fusion events are needed to release 1.0 J of energy?
- 3 Explain why a fusion reactor must confine plasma instead of letting it touch the container walls, and include the role of temperature in your answer.