Doubly magic tin-132

Article By:

Jones, Kate L. Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee.

Last reviewed:2012

DOI:https://doi.org/10.1036/1097-8542.YB120404

The year 2011 marks the centenary of the discovery of the atomic nucleus. In 1911, Ernest Rutherford, with his colleagues Hans Geiger and Ernest Marsden, demonstrated that at the heart of the atom lies the positively charged nucleus. In the intervening hundred years, much has been learned about the structure of the nucleus itself and the variations in the nature of different species of nuclei as the number of nucleons (neutrons or protons) is varied. For more than 50 years, the nuclear shell model has stood as a cornerstone of nuclear structure physics. Just as the inertness of noble gases and the volatility of alkali metals can be explained in terms of electrons moving in a well-defined structure of orbits, nucleons in nuclei occupy quantum shells. The shell model, developed by Maria Goeppert-Mayer, J. Hans D. Jensen, and others describes individual nucleons moving in an average potential generated by all the other nucleons. This model explains the existence of particularly well-bound nuclei with “magic” numbers of protons (Z) or neutrons (N). The standard magic numbers are 2, 8, 20, 28, 50, 82, and 126. However, recent experiments have demonstrated that the structure of shells in exotic light nuclei is markedly different to that for stable nuclear species. For example, the neutron magic numbers 20 and 28 disappear altogether for the most neutron-rich nuclei, and new shell gaps seem to emerge. No such experimental evidence has been observed in the heavier nuclei, and indeed such effects are expected only in isotopes beyond current experimental reach. It is therefore important to test the magicity of neutron-rich nuclei in the region around the nuclide tin-132 (¹³²Sn), whose proton number, Z = 50, and neutron number, N = 82, are both standard magic numbers, to study the evolution of shell structure away from stability.

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