<P> Alpha decay or α - decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or' decays' into an atom with a mass number that is reduced by four and an atomic number that is reduced by two . An alpha particle is identical to the nucleus of a helium - 4 atom, which consists of two protons and two neutrons . It has a charge of + 2e and a mass of 4u . For example, uranium - 238 decays to form thorium - 234 . Alpha particles have a charge + 2, but as a nuclear equation describes a nuclear reaction without considering the electrons--a convention that does not imply that the nuclei necessarily occur in neutral atoms--the charge is not usually shown . </P> <P> Alpha decay typically occurs in the heaviest nuclides . Theoretically, it can occur only in nuclei somewhat heavier than nickel (element 28), where the overall binding energy per nucleon is no longer a minimum and the nuclides are therefore unstable toward spontaneous fission - type processes . In practice, this mode of decay has only been observed in nuclides considerably heavier than nickel, with the lightest known alpha emitters being the lightest isotopes (mass numbers 106--110) of tellurium (element 52). Exceptionally, however, beryllium - 8 decays to two alpha particles . </P> <P> Alpha decay is by far the most common form of cluster decay, where the parent atom ejects a defined daughter collection of nucleons, leaving another defined product behind . It is the most common form because of the combined extremely high binding energy and relatively small mass of the alpha particle . Like other cluster decays, alpha decay is fundamentally a quantum tunneling process . Unlike beta decay, it is governed by the interplay between both the nuclear force and the electromagnetic force . </P> <P> Alpha particles have a typical kinetic energy of 5 MeV (or ≈ 0.13% of their total energy, 110 TJ / kg) and have a speed of about 15,000,000 m / s, or 5% of the speed of light . There is surprisingly small variation around this energy, due to the heavy dependence of the half - life of this process on the energy produced (see equations in the Geiger--Nuttall law). Because of their relatively large mass, + 2 electric charge and relatively low velocity, alpha particles are very likely to interact with other atoms and lose their energy, and their forward motion can be stopped by a few centimeters of air . Approximately 99% of the helium produced on Earth is the result of the alpha decay of underground deposits of minerals containing uranium or thorium . The helium is brought to the surface as a by - product of natural gas production . </P>

What daughter nuclide is produced from the alpha decay of th
find me the text answering this question