Nuclear Processes

Abstract

The energy source that powers the luminosity of stars is nuclear fusion. Atomic nuclei consist of protons and neutrons that are bound tightly together in a volume a few femtometers across. The strong nuclear force that interacts with nucleons and binds them must be stronger than the repulsive electrostatic force that the protons feel in such close proximity to each other. The nuclear force cannot be long range or it would draw all nucleons in the universe together. A simplified cartoon of the potential felt by a proton in and near a nucleus is shown in Fig. 7.1. As a proton approaches it feels a repulsive electrostatic potential due to the net positive charge of the protons already in the nucleus. Once it gets close enough, the strong nuclear force takes over and the potential becomes negative and the proton becomes bound. If the new nucleus is less massive than iron, the rest mass energy of the new nucleus is lower than the combined rest masses of the incoming proton and the old nucleus. This is a direct result of the release of the binding energy.