CNRS Université Bordeaux

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The seniority quantum number in nuclei

Vendredi 1 juillet 2011 à 11h00 - Salle des Séminaires

Seniority in the structure of nuclei refers to the number of nucleons that are not in pairs coupled to angular momentum J=0, and therefore it probes the most important two-body correlation within nuclei, “pairing”. Racah first introduced seniority in 1943 for the classification of complex atomic spectra and adapted it a few years later in the context of nuclear physics. In this talk I will briefly review the conditions for seniority conservation. The more recently discovered possibility of “partial” seniority conservation will be presented when most states are of mixed seniority but some remain pure. This explains the occurrence of nuclear seniority isomers, characterized by electromagnetic decay hindered by selection rules related to seniority. A simple analysis is presented of their possible formation with reference to the nickel isotopes 70-76Ni and the N=50 isotones from molybdenum to cadmium. It is shown that the existence of seniority isomers is predominantly governed by the quadrupole pairing matrix element of the nucleon-nucleon interaction.