Some basics of nuclear physics

A nice primer on the basics of nuclear science can be found here, on Lawrence Berkeley National Laboratory's Web site.  Wikibooks also has a helpful article on nuclear structure. The following discussion is an attempt to summarize as best I can some of the important points I picked up from reading these and related articles.

The electromagnetic force governs the attraction and repulsion of charged particles, e.g., electrons and protons and protons with one another, but also that involving more exotic particles, such as a muon with a proton.  The strong force governs interactions between nucleons—neutrons and protons.  The carrier of the electromagnetic force can be thought of as a virtual photon.  The force carrier for the strong force is a pion.  Because pions are massive, the strong force is effective only over short distances, and because photons are nearly massless, the electromagnetic force operates over long distances.

The strong force holds nucleons together in a nucleus, but the electromagnetic force repels protons from one another.  In a stable nucleus with small atomic mass, the ratio of neutrons to protons is around 1.  In a stable nucleus with larger atomic mass, the ratio moves towards 1.5.  The nuclear stability curve plots out the ratio for stable isotopes.  The larger the nucleus, the more neutrons are needed to counteract the electromagnetic force and keep the nucleus from fissioning into smaller nuclei.  All elements up to iron are generated in a star like the sun.  Fusion is exothermic in these instances.  Elements of atomic number greater than iron (26) are created in supernovae, where there is sufficient energy to result in the fusion of heavier elements.  At some point past iron along a curve of the binding energies for the various elements, fission becomes exothermic rather than endothermic, and fusion becomes endothermic rather than exothermic.  (This is relevant to the discussion of the creation of copper from the fusion of hydrogen and nickel.)

There are three types of radioactive decay that occur in nuclei that arise from different transitions that can happen within them.  Alpha decay involves the emission of a helium nucleus.  During alpha decay, transmutation occurs and the atomic mass and the atomic number (number of protons) decrease.  Beta decay is caused by the weak force and involves the decay of a neutron into a proton, an electron and an electron antineutrino.  Beta decay also results in transmutation, yielding an increase in the atomic number.  For example, carbon-14, an isotope of carbon with a half-life of thousands of years, beta decays to become nitrogen-14.  Evidently the proton is not ejected in the process.  A third type of radioactive decay is gamma decay, which involves the emission of a gamma ray photon.  It occurs when a nucleus transitions from a higher energy state into a lower energy state.  One explanation was that the neutrons and protons move around into a more stable configuration.  Importantly, radioactive decay pertains to the nucleus and not the orbiting electrons.  If I understand what is going on, in beta decay, for example, the electron comes from the nucleus itself and not one of the orbits.

The mass of a neutron is slightly heavier than that of a proton.  So when you have beta decay, and the neutron changes to a proton, there is a release of energy which is carried by the nearly massless electron and the electron antineutrino.  Energy at these levels is measured in electron volts, eV, and mega-electron volts, MeV.  Energy in the realm of electron volts is found in chemical reactions, and energy in the realm of MeV is found in nuclear reactions.  An electron volt is the energy required to move an electron through a potential difference of one volt.  In many contexts energy is used almost interchangeably with mass.  Einstein's famous relation E = mc^2 governs the translation between energy and mass when the actual unit of measure is of interest.

Inverse beta decay is the "decay" of a proton into a neutron, with the emission of a positron and an electron neutrino.  In contrast to beta decay, inverse beta decay requires energy rather than releasing it.  Inverse beta decay occurs through the electron capture process, or K-capture.

Binding energy is the energy required to hold a nucleus together.  In cases where the mother nucleus in a decay has greater overall binding energy than daughter nuclei, kinetic energy will be released.  In cases where the mother nucleus has less binding energy than the daughter nucleus (or nuclei?), presumably kinetic energy will have been captured, although I did not specifically read this.