Alpha decay
All nuclei with the atomic number Z>82, are considered unstable. These are considered “neutron rich” and undergo the decay process by emitting a particle containing two neutrons and two protons.
Alpha decay is the process in which an alpha particle (containing two neutrons and two protons) is ejected from the nucleus. Alpha particle is identical to the nucleus of a helium atom, being the most stable nucleus so far.
Alpha decay occurs in nuclei of heavy elements, like radium, uranium, thorium etc. When a nucleus of Ra (Radium) decays, it emits an alpha particle and becomes a Rn (Radon) nucleus, as described in the (Fig. 1 – Alpha decay). In general, during alpha decay the atomic number (Z) is reduced by two units and the mass number (A), by four units. For example, alpha decay generates Rn-222 with the atomic number 86 and the mass number 222 from Ra-226 with the atomic number 88 and the mass number 226, as shown in Fig. 1.
Alpha particles are very heavy and contain high amounts of energy (4-10MeV). Their speed is app. 20000km/s and they interact with matter, causing much ionization in a very short distance. They usually pass short distances (a 5 MeV alpha particle will travel about 20 micrometers in silicon) and could be stopped by a sheet of paper. Alpha particles do not produce Bremsstrahlung radiation, when slowing down.
Alpha particles are not generally dangerous, unless the source is ingested or inhaled, since alpha radiation is the most destructive form of ionizing radiation.
