Silicon-burning Process - Binding Energy

Binding Energy

The graph above shows the binding energy of various elements. Increasing values of binding energy can be thought of in two ways: 1) it is the energy required to remove a nucleon from a nucleus, and 2) it is the energy released when a nucleon is added to a nucleus. As can be seen, light elements such as hydrogen release large amounts of energy (a big increase in binding energy) as nucleons are added—the process of fusion. Conversely, heavy elements such as uranium release energy when nucleons are removed—the process of nuclear fission. In stars, rapid nucleosynthesis proceeds by adding helium nuclei (alpha particles) to heavier nuclei. Although nuclei with 58 and 62 nucleons have the very lowest binding energy, fusing a helium nucleus into nickel-56 (14 alphas) to produce the next element—zinc-60 (15 alphas)—actually requires energy rather than releases any. Accordingly, nickel–56 is the last fusion product produced in the core of a high-mass star. Decay of nickel-56 explains the large amount of iron-56 seen in metallic meteorites and the cores of rocky planets.