<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 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>
an alpha particle has a mass number of
an alpha particle has a mass number of
4u
4u