Island of stability

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The island of stability is a term from nuclear physics that describes the possibility of elements with particularly stable magic numbers of protons and neutrons. Existing on this "island" would allow the isotopes of some transuranium elements to be far more stable than others; that is, to decay much more slowly with half-lives of at least minutes or days as compared to seconds. Some theorists have suggested the possibility that the half-lives of these isotopes could be on the order of millions of years.[1]

Contents

Theory and origin

The possibility of an "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 large energy gap. So when the number of neutrons and protons completely fill the energy levels of a given shell in the nucleus, the binding energy per nucleon will reach a local maximum and thus that particular configuration will have a longer lifetime than nearby isotopes that do not have filled shells.[2]

A filled shell would have "magic numbers" of neutrons and protons. One possible magic number of neutrons for spherical nuclei is 184, and some possible matching proton numbers are 114, 120 and 126 – which would mean that the most stable spherical isotopes would be ununquadium-298, unbinilium-304 and unbihexium-310. Of particular note is Ubh-310, which would be "doubly magic" (both its proton number of 126 and neutron number of 184 are thought to be magic) and thus the most likely to have a very long half-life. (The next lighter doubly-magic spherical nucleus is lead-208, the heaviest stable nucleus and most stable heavy metal.)

Recent research indicates that large nuclei are deformed, causing magic numbers to shift. Hassium-270 is now believed to be a doubly-magic deformed nucleus, with deformed magic numbers 108 and 162.[3][4] However, it has a half-life of only 3.6 seconds.[5]

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