The observed forms of decay are alpha decay, beta decay, neutron emission[?], proton emission[?], and spontaneous fission[?]. The latter three forms of decay occur very quickly within products of nuclear reactions, and hence are not often seen on earth outside a nuclear reactor. By contrast alpha and beta decay are seen in the decay chains of radioactive materials.
Radioactive decay is observed astronomically in supernova, and the light curve of supernova is generated via the decay of radioactive nickel into iron.
Many radionuclides have several different modes of decay, each with its own probability. Bismuth-212, for example, has three.
All radioactive decay is also associated with emission of gamma radiation in varying degrees.