Island of stability
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Template:Reqimage The island of stability is a term from nuclear physics, which describes the possibility of elements which have particularly stable "magic numbers" of protons and neutrons. This would allow certain isotopes of some transuranic elements to be far more stable than others, and thus decay much more slowly.
The idea of the island of stability was first proposed by Glenn T. Seaborg. The hypothesis is that the atomic nucleus is built up in "shells" in a manner similar to the electron shells in atoms. In both cases shells are just groups of quantum energy levels that are relatively close to each other. Energy levels from quantum states in two different shells will be separated by a relatively larger energy gap. So when the numbers of neutrons and protons completely fill the energy levels of a given shell in the nucleus, then the binding energy per nucleon will reach a local minimum and thus that particular configuration will have a longer lifetime than nearby isotopes that do not have filled shells.
A filled shell would have "magic numbers" of neutrons and protons. One possible magic number of neutrons is 184, and some possible matching proton numbers are 114, 120 and 126 — which would mean that the most stable possible isotopes would be ununquadium-298, unbinilium-304 and unbihexium-310. None of these isotopes have yet been produced. Isotopes of ununquadium, with 114 protons but fewer than 184 neutrons, have been produced and are significantly slower to decay than isotopes of nearby elements on the periodic table.
The term "particularly stable" is in comparison to the half-lives of slightly lighter or heavier elements; the half-lives of elements in the island of stability are still expected to be measured in fractions of a second, or perhaps measured in days, though some theoretical possibilities include much longer periods.