High-seniority states in spherical nuclei: Triple pair breaking in tin isotopes, Alain Astier, CNRS/IN2P3 - CSNSM Orsay, France − The identification of states involving many identical nucleons in the same orbit j, i.e. states with the jn configuration, is a straightforward application of the nuclear shell model.  While there are numerous examples of states with seniority v=2 in the literature, only a few states with v=4 are known:  The 10+ and 12+ of the (pi g9/2)4 configuration have been identified in two N=50 isotones, 94Ru and 96Pd, and the 16+ state of the (pi h11/2)4 configuration in the N=82 nucleus, 150Er.  The Sn isotopic chain is a good laboratory to study the case of (nu h11/2)n, particularly the highest spin states expected for n=4,5 and 6. For that purpose their yrast states have to be populated with enough intensity to be measured.


In our work, the 119-126Sn nuclei have been produced as fission fragments in two reactions induced by heavy ions: 12C+238U at 90 MeV bombarding energy, 18O+208Pb at 85 MeV.  Their level schemes have been built from gamma rays detected using the Euroball array.  High-spin states located above the long-lived isomeric states of the even-A and odd-A 120-126Sn nuclei have been identified. Moreover isomeric states lying around 4.5 MeV have been established in the even-A 120-126Sn from the delayed coincidences between the fission fragment detector SAPhIR and the Euroball array.  All the states located above 3-MeV excitation energy are ascribed to several broken pairs of neutrons occupying the h11/2 orbit.  The maximum value of angular momentum available in such a high-j shell, i.e. for mid-occupation and the breaking of the three neutron pairs (seniority v=6), has been identified [1].


In this talk we will present and discuss this process which is observed for the first time in spherical nuclei.


[1] A. Astier et al. submitted to PRC (December 2011).