Inner binding energy of atomic nuclei. The nuclear building blocks show various degrees of mutual binding from one atom type to another. The maximum binding energy per nuclear building block is within the range of the mass number 60. By means of nucleus conversion, energy can therefore be obtained either by fission of heavy nuclei such as uranium or by fusion of lighter nuclei such as hydrogen. The fission of 1 kg U-235 supplies about 23 million kWh, during the fusion of deuterium and tritium (DT-reaction) to 1 kg helium, energy of about 120 million kWh is released. In contrast, the combustion of 1 kg coal supplies only about 10 kWh. (See ‘fusion’ and ‘nuclear fission’.)

Nuclear binding energy depending on the mass number of the nucleus of the atom