Chapter 17 · Radioactivity and Nuclear Chemistry
17.9Nuclear Fusion: The Power of the Sun
8 min · two checks
Predict
Why does fusion demand enormous temperature?
The idea
- Define fusion and contrast it with fission.
- Explain the electrostatic barrier.
Fusion joins light nuclei into a heavier one. In the Sun, hydrogen nuclei ultimately become helium, and the product’s mass is slightly less than the reactants’. The difference leaves as energy. Per gram, fusion of light nuclei releases even more energy than fission of uranium, and the fuel is astonishingly abundant. The waste profile is different too: the main ash of hydrogen fusion is helium, not a spectrum of long-lived fission fragments.
The difficulty is the start. Both nuclei are positively charged and repel. Fusion wins only when they approach within the reach of the short-range nuclear force, which on Earth means confining a plasma at temperatures of tens of millions of degrees. Weapons can do that for an instant with a fission trigger. Power plants that do it continuously are still an engineering project, not a source you can plug in tonight. The attraction of the project is the fuel and the energy density, not a claim that it is already easy.
Keep these
- Fusion combines light nuclei. The Sun turns hydrogen into helium.
- Like charges repel, so fusion needs extreme collision energy.
- Mass defect becomes energy. The ash is not the same as fission waste.