Mid Term Review

Electromagnetic moments in the 132Sn region: testing the shell model and the emergence of collectivity

Mr Timothy Gray
Department Nuclear Physics

The isotope 132Sn appears to be one of the most robust examples of a double shell closure. As a result the surrounding region provides excellent opportunities to test shell-model predictions and investigate the emergence of collectivity as protons and neutrons are added to or removed from 132Sn. An overview will be given and two examples of experimental studies in the region presented.  A Coulomb excitation experiment of radioactive 129Sb allows the measurement of B(E2) excitation strengths, which are compared against particle-core coupling and state-of-the-art shell-model calculations. The results indicate a significant enhancement in the quadrupole excitation, in stark contrast to the predictions of the long standing particle-core coupling scheme, and providing valuable insight into the emergence of collectivity.  A second experiment studying beta-decay into 138Xe aims to measure the magnetic moment of the first excited 2+ state, and provides a variety of spectroscopic information: gamma-gamma angular correlations, and extensions to the established level scheme.

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