• Nuclear fusion is the process of joining two smaller nuclei to form a more stable nucleus.
• The nucleus formed is more stable as it has a higher binding energy than the nuclei used to form it.
• The mass defect , arising due to the higher binding energy gets released as energy, and can be calculated as .

For example , to form a deuterium – a proton and neutron is required in the nucleus.

• mass of proton (m_p) = 1.007276u
• mass of neutron (m_n) = 1.008665u
• mass of deuterium nucleus = 2.013553u
• Thus mass defect = 1.007276u + 1.008665u – 2.013553u = 0.002388u
• Note : 1 atomic mass unit, u = 1.661 x 10^-27 kg.
• This mass defect will get released as energy : E = mc² = 0.002388 x 1.661 x 10^-27 kg x (3 x 10⁸ms^-1)²

Another famous example is formation of helium nucleus from nuclei of deuterium and tritium .

Extract from Physics Stage 6 Syllabus © 2017 NSW Education Standards Authority (NESA)