Appendix A: Nuclear physics in brief

Each type of atom has a nucleus consisting of a characteristic number of protons and neutrons that is characteristic of that type of nucleus. Nuclear physicists call this specific nucleus a nuclide.

In nature many different nuclides exist, but thay can also be made in the laboratory by bombarding certain types of material with protons or neutrons. The majority of the artificial nuclides and some natural nuclides are unstable: they transform spontaneously into other nuclides whilst emitting radiation. This phenomena is called radioactive decay, and nuclides that exhibit such behaviour are called radionuclides.

Each radionuclide has its own characteristic way of decaying: giving off a specific kind of radiation with a specific energy.
The rate with which the nuclide decays - expressed as its half-life - is unique for that material. thus, for the different requirements of nuclear medical treatment, different radionuclides are selected. In professional language these are usually referred to as radioisotopes or, simply, isotopes.