Double Magic
Nuclei which have neutron number and proton (atomic) numbers each equal to one of the magic numbers are called "double magic", and are especially stable against decay. Examples of double magic isotopes include helium-4 (4He), oxygen-16 (16O), calcium-40 (40Ca), calcium-48 (48Ca), nickel-48 (48Ni) and lead-208 (208Pb).
Double-magic effects may allow existence of stable isotopes which otherwise would not have been expected. An example is calcium-40 (40Ca), with 20 neutrons and 20 protons, which is the heaviest stable isotope made of the same number of protons and neutrons. Both calcium-48 (48Ca) and nickel-48 (48Ni) are double magic because calcium-48 has 20 protons and 28 neutrons while nickel-48 has 28 protons and 20 neutrons. Calcium-48 is very neutron-rich for such a light element, but like calcium-40, it is made stable by being double magic. Similarly, nickel-48, discovered in 1999, is the most proton-rich isotope known beyond helium-3.
Magic number shell effects are seen in ordinary abundances of elements: it is no accident that helium-4 (4He) is among the most abundant (and stable) nuclei in the universe and that lead-208 (208Pb) is the heaviest stable nuclide.
Magic effects can keep unstable nuclides from decaying as rapidly as would otherwise be expected. For example, the nuclides tin-100 (100Sn) and tin-132 (132Sn) are interesting examples of doubly magic isotopes of tin that are unstable; however they represent endpoints beyond which stability drops off rapidly.
In December 2006 hassium-270 (270Hs), with 108 protons and 162 neutrons, was discovered by an international team of scientists led by the Technical University of Munich having the unusually long half-life of 22 seconds. Hassium-270 evidently forms part of an island of stability, and may even be double magic.
Read more about this topic: Magic Number (physics)
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