Figure 9.1 Approximate Wavelengths and Photon Energies of Electromagnetic Radiation. According to the quantum theory model, electromagnetic radiation consists of bundles of energy called photons, which travel at the speed of light. Gamma rays result from transformations that take place in the nucleus of an atom, and X-rays are formed by interactions outside the nucleus. They carry an electrical charge of -1. Alpha particles are heavier.
Neutrons are approximately equal in mass to the proton and have no electric charge.
A nuclide is a species of atom characterized by the constitution of its nucleus, as specified by the number of protons, the number of neutrons, and the energy content. A radionuclide is a nuclide that spontaneously emits radiation in the form of electromagnetic or particulate radiation. The emission of radiation by atoms is complex. Positron emission results in the production of gamma photons. Different atoms of a given radionuclide may emit different combinations of radiation types, or emissions of the same type but differing in energy or frequency.