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Radioactive decay is the process by which radionuclides
decay, emitting ionizing radiation. Such nuclear reactions involve a change in the composition of the nucleus, in contrast to chemical reactions which involve only an exchange or sharing of electrons.
There are forces in the nucleus that oppose each other, the strong force
holding protons and neutrons to each
other and the electrostatic force of protons repelling other protons.
Under certain arrangements of protons and neutrons the electrostatic force can cause instability in the nucleus causing it to
decay. It will continue to decay until it reaches a stable combination.
The observed forms of decay are alpha decay, beta decay, electron capture, neutron emission, positron emission, proton emission, and
spontaneous fission. The latter five 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.
Neutron emission is also important as the most important reason for the difficulty of manufacturing a nuclear bomb from lower grades of plutonium.
Radioactive decay is observed astronomically in supernovae. The light curve of a 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.
Nearly all decay products are themselves radioactive, giving rise to
decay chains which eventually end in a stable nuclide.
This decay has been deemed by some utterly random, and has been used by some in
random number
generation.
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