# Nuclear Fission vs Fusion

**Nuclear fission and fusion** reactions harness the strong nuclear force – the phenomenal ‘glue’ which holds atoms together. To produce a fission reaction, a neutron is fired at an atomic nucleus, smashing it apart and leaving radioactive nuclei, neutrons and energy.

In a fusion reaction, two or more nuclei are combined; they merge into one heavy nucleus, freeing neutrons and huge amounts of energy in the process. Coaxing nuclei together requires lots of heat and pressure since their positive charges naturally repel each other.

So how do these reactions generate such epic amounts of energy? An atom’s mass is more than just the sum of its parts. Strangely enough, a significant proportion of a nucleus’s mass is made up by the strong nuclear force – the glue that binds it together.

So although the number of protons and neutrons is the same before and after a fission or fusion reaction has taken place, a minute amount of that subatomic glue – and therefore mass – is liberated.

Both fission and fusion reactions convert this mass into energy, as described by Einstein’s famous E=mc2 equation. The constant c in this formula represents the speed of light, so c2 is a pretty big number! In other words, just a tiny bit of mass can produce an extraordinary amount of energy.

## Nuclear fission

**Definition:** The splitting of an atom’s nucleus into smaller constituent parts

**Occurrence:** Rare in nature, now found most often in nuclear power stations

**Conditions:** You need enough fissile matter and a high-powered neutron

**Products:** Neutrons, radioactive nuclei and energy

**Energy requirement: **Small, just enough to fire neutrons at a nucleus

**Energy released:** Over 100 million times more energy than that released from the same mass of coal

## Nuclear fusion

**Definition:** The joining of two or more atomic nuclei to form a single heavy nucleus

**Occurrence:** Takes place at the heart of stars

**Conditions:** Extremely high temperature and pressure

**Products:** Heavier nuclei, neutrons and energy

**Energy requirement**: Very large – enough to overcome the nuclei’s natural repulsion

**Energy released:** Three or four times more energy created than a fission reaction