Island of stability

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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 large 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. 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 nucleus is Lead-208, the second heaviest stable nucleus and most stable heavy metal. None of these isotopes has 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 nuclei on the periodic table.

The half lives of these elements are uncertain. Many physicists think they are relatively short, on the order of minutes, hours, or perhaps days. However, some theoretical calculations indicate that their half lives may be long (some calculations put it on the order of 10⁹ years)^{[[Citing sources citation needed]]}. Many chemists and science fiction writers have claimed that these elements could have unusual properties, and, if long lived enough, various applications (such as targets in nuclear physics and neutron sources). However after the isolation of several of these elements, this possiblity is becoming more distant. A memorable faliure is that of Ununpentium, which has featured in many science fiction novels as a UFO powersource.

Island of relative stability

²³²Th (thorium), ²³⁵U and ²³⁸U (uranium) are the only naturally occurring isotopes beyond bismuth that are relatively stable over the current lifespan of the universe. All other isotopes beyond bismuth are relatively or very unstable. So the main periodic table ends at bismuth, with an island at thorium and uranium. Between bismuth and thorium there is an island of severe instability, which renders such elements as astatine, radon, and francium extremely short-lived relative to all but the heaviest elements found so far.

The relatively unstable elements reach up to ²⁵⁷Fm (fermium), after which they get very unstable due to spontaneous fission until somewhat more stable, spherical nuclei are obtained at the island of stability, set in the ocean of instability.

Island of stability

Island of relative stability

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