Alpha particles irradiation: a paradigm change in cancer brachytherapy

All matter is composed of individual entities called elements. Each element is distinguishable from the others by the physical and chemical properties of its basic component – the atom. Each atom consists of a small central core, the nucleus (radius 10-14 m), where most of the atomic mass is located and a “cloud” of electrons moving in orbits (radius 10-10 m) around the nucleus. The properties of the atoms are derived from the constitution of their nuclei and the number and organization of the orbital electrons. The nucleus contains two kinds of fundamental particles: protons (positively electrically charged) and neutrons (no charge). The number of protons is equal to that of the electrons, making the atom electrically neutral. Thus represented, the atoms are also called nuclides. On the basis of different proportions of neutrons and protons in the nuclei, atoms have been classified into the following categories: isotopes (nuclei having the same numbers of protons but different numbers of neutrons), isotones (same numbers of neutrons but different numbers of protons), isobars (same total numbers of protons and neutrons), and isomers (same numbers of protons and neutrons). Certain combinations of neutrons and protons result more in stable (non-radioactive) nuclides than others.