First exploration of neutron shell structure below lead and beyond $N=126$

T. L. Tang, B. P. Kay, C. R. Hoffmann, J. P. Schiffer, D. K. Sharp, L. P. Gaffney, S. J. Freeman, M. Mumpower, A. Arokiaraj, E. F. Baader, P. A. Butler, W. N. Catford, G. de Angelis, F. Flavigny, M. D. Gott, E. T. Gregor, J. Konki, M. Labiche, I. H. Lazurus, P. T. MacGregor, I. Martel, R. D. Page, Zs. Podolyak, O. Poleshchuk, R. Raabe, F. Recchia, J. F. Smith, S. V. Szwec, J. Yang

Published PRL 124, 062502 (2020)

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 $A\sim 190$. 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 $^{207}$Hg have been probed using the neutron-adding (d,p) reaction in inverse kinematics. The radioactive beam of $^{206}$Hg was delivered to the new ISOLDE Solenoidal Spectrometer at an energy above the Coulomb barrier. The spectroscopy of $^{207}$Hg 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.




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