Nuclear Fusion


(a) With reference to the process of nuclear fusion, explain why energy is released when two small nuclei join together, and why it is difficult to make two nuclei come together

When two small nuclei fuse together there is a decrease in mass between the reactants and products. This relates to an increase in mass difference. This mass is converted into energy which is released when the fusion occurs. The stability is greater for nucleus after fusion, this is shown by an increase in the binding energy per nucleon in the product of the nuclear reaction. It is difficult to make the two nuclei come together as they are both positive and have to overcome the force of electrostatic repulsion

(3 marks MAX)

(b) A fusion reaction takes place when two deuterium nuclei join, as represented by

mass of deuterium nucleus = 2.01355 u

mass of helium-3 nucleus = 3.01493 u

mass of neutron = 1.00867 u


(i) the mass difference produced when two deuterium nuclei undergo fusion,

Δm = 2 × (2.01355) – (3.01493 + 1.00867)

Δm = 3.5 × 10–3 u (5.81 × 10–30 kg)

(ii) the energy released, in J, when this reaction takes place.

ΔE = 3.5 × 10–3 × 931.3 MeV

ΔE = 3.26 MeV = 3.26 × 106 × 1.6 × 10–19

ΔE = 5.22 × 10–13 J

(3 marks)

(Total 6 marks)