The table of nuclides
The smallest components of matter, the atoms, consist of an electronshell and an atomic nucleus. The nucleus, in turn, is composed of positively charged protons and uncharged neutrons. Depending on the combination of protons and neutrons we obtain different nuclides listed in the table of nuclides. Common and well known are mainly the stable nuclides marked with grey in the table. Beside this there also exists a wide variety of instable nuclides that decay to stable nuclides after some time emitting radioactive radiation.
Types of radioactive decay
α-decay: During α-decay an α-particle splits from the parent nuclide. An α-particle consists of two protons and two neutrons and equates to an helium nucleus. The mass number of the nuclide decreases by 4 while the proton number decreases by 2. Since the α-particle is double positively charged the electron shell of the daughter nuclide has to release two electrons. Alpha radiation is a short range radiation that can be screened by a piece of paper or some centimeters of air.
β-decay: The β-decay is a process in which a neutron is converted to a proton. According to the standard model of physics nucleons consist of three quarks, the proton exhibiting the configuration uud and the neutron the configuration udd. Via the weak interaction a d-quark can be transformed in a u-quark mediated by a W--boson, whereas an electron and an anti-neutrino is emitted. In total the mass number of the decaying nuclide remains constant and the proton number increased by 1. In the opposite case a proton can be converted into a neutron under emission of a neutrino and an anti-electron, named positron. This process is called β+-decay respectively. Some nuclides also show double beta decay with two β-decays at the same time. Another form of beta decay is electron capture where the nucleus uses a electron of the electron shell to convert a proton into a neutron while emitting a neutrino.
γ-decay: Nuclides that remain in a metastable state after an α- or β-decay, are called isomers and can change over to the energetic ground state via γ-decay. Thereby energy-rich photons with energies higher than 200 MeV are emitted as gamma radiation.
Some rare nuclides show further types of decay:
Spontaneous fission occurs at nuclides with higher proton number like thorium or uranium where the parent nuclide splits into two smaller nuclides.
During cluster decay a particle consisting of protons and neutrons is emitted from the parent nuclide like in alpha decay. This process is called cluster decay if the emitted particle is heavier than a alpha particle e.g. nuclei of carbon or neon atoms. A few nuclides also decay via proton or neutron emission emitting one or two protons or neutrons respectively.