Nuclear fusion, computer artwork. At left are the atomic nuclei of deuterium (top left) and tritium (bottom left). Atomic nuclei consist of protons (white and purple) and neutrons (pink). The nuclei fuse, forming lithium-5 (centre). This is a highly unstable isotope, which quickly decays into helium-4 (top right) and a neutron (bottom right). This decay results in an overall release of energy.