Abstract
A dipole band of six transitions built upon a firmly established Iπ=31/2− isomeric state has been identified in Pb189 using recoil-isomer tagging. This is the lightest odd-mass Pb nucleus in which a dipole band is known. The dipole nature of the new transitions has been confirmed through angular-intensity arguments. The evolution of the excitation energy and the aligned-angular momentum of the states in the new dipole band are compared with those of dipole bands in heavier, odd-mass lead isotopes. This comparison suggests that the new band in Pb189 is based upon a π[s1/2−2h9/2i13/2]11−⊗ν[i13/2+−1]13/2+ configuration. However, the increased aligned-angular momentum in Pb189 may suggest evidence for a reduced repulsive proton/neutron-hole interaction compared to dipole bands in the heavier mass isotopes.Received 1 May 2015Revised 12 October 2015DOI:https://doi.org/10.1103/PhysRevC.92.054312©2015 American Physical Society
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