Atoms & Energy

This is an atom. It has protons with positive charge and neutrons with neutral charge. They manage to clump together despite the Coulmmb repulsive between like charges. Different elements have different numbers of protons. Isotopes of an element have different numbers of neutrons. Not all configurations are stable.

Of all the known elements, iron is the most stable element around. Splitting isotopes heavier than iron or fusing lighter ones yields isotopes with lower binding energy per nucleon. Energy is conserved, and therefore some energy must be released. If all you have is iron, you’re out of luck. There’s no excess binding energy available.

Below, we see the binding energy per nucleon (protons and neutrons) for each element. Binding energy is the energy required to take apart the atom into its constituent particles.

When we look at an atom, its mass is less than the sum of the masses of its constituent particles. That missing mass is the binding energy keeping the particles together, as related by E=mc2, where E is the nuclear binding energy, m is the difference in mass, and c is the speed of light. Elements like Iron appear to be low energy or low mass relative to heavy elements like Uranium.

A higher binding energy per nucleon means the atom is more stable and efficient at keeping itself together. If we go from lower to higher binding energy, more energy is available for something else. Equivalently, if we go from high to low mass per nucleon, we are releasing stored energy.