First Exploration of Neutron Shell Structure below Lead and beyond N=126

The nuclei below lead but with more than 126 neutrons are crucial to an understanding of the astrophysical r process in producing nuclei heavier than A similar to 190. Despite their importance, the structure and properties of these nuclei remain experimentally untested as they are difficult to produce in nuclear reactions with stable beams. In a first exploration of the shell structure of this region, neutron excitations in Hg-207 have been probed using the neutron-adding (d,p) reaction in inverse kinematics. The radioactive beam of Hg-206 was delivered to the new ISOLDE Solenoidal Spectrometer at an energy above the Coulomb barrier. The spectroscopy of Hg-207 marks a first step in improving our understanding of the relevant structural properties of nuclei involved in a key part of the path of the r process.