The notation that is used to represent an alpha particle is 4.2 H [THAT IS, AN HELIUM ATOM].
Alpha particle is formed when a radioactive element undergoes an alpha radioactive decay. An alpha radioactive decay is the type of decay in which an atomic nucleus gives off an helium nucleus and is thereby transformed into another element, which has a mass number that is less than the original element. An alpha particle is an helium nucleus, which contains two positively charged proton and two neutral neutron; it has an overall charge of +2 and a mass number of 4.