Nuclear Fission Versus Nuclear Fusion

Nuclear fission and nuclear fusion both are nuclear phenomena that release large amounts of energy, but they are different processes which yield different products. Learn what nuclear fission and nuclear fusion are and how you can tell them apart.

Nuclear Fission

Nuclear fission takes place when an atom's nucleus splits into two or more smaller nuclei. These smaller nuclei are called fission products. Particles (e.g., neutrons, photons, alpha particles) usually are released, too. This is an exothermic process releasing kinetic energy of the fission products and energy in the form of gamma radiation. Fission may be considered a form of element transmutation since changing the number of protons of an element essentially changes the element from one into another.

Nuclear Fission Example

²³⁵₉₂U + ¹₀n → ⁹⁰₃₈Sr + ¹⁴³₅₄Xe + 3¹₀n

Nuclear Fusion

Nuclear fusion is a process in which atomic nuclei are fused together to form heavier nuclei. Extremely high temperatures (on the order of 1.5 x 10⁷°C) can force nuclei together. Large amounts of energy are released when fusion occurs.

Nuclear Fusion Examples

The reactions which take place in the sun provide an example of nuclear fusion:

¹₁H + ²₁H → ³₂He

³₂He + ³₂He → ⁴₂He + 2¹₁H

¹₁H + ¹₁H → ²₁H + ⁰₊₁β

Distinguishing between Fission and Fusion

Both fission and fusion release enormous amounts of energy. Both fission and fusion reactions can occur in nuclear bombs. So, how can you tell fission and fusion apart?

• Fission breaks atomic nuclei into smaller pieces. The starting elements have a higher atomic number than that of the fission products. For example, uranium can fission to yield strontium and krypton.

• Fusion joins atomic nuclei together. The element formed has more neutrons or more protons than that of the starting material. For example, hydrogen and hydrogen can fuse to form helium.