Laser spectroscopy of neutron-rich $^{207,208}$Hg isotopes: Illuminating the kink and odd-even staggering in charge radii across the $N=126$ shell closure
/ Authors
T. D. Goodacre, A. Afanasjev, A. Barzakh, B. Marsh, S. Sels, P. Ring, H. Nakada, A. Andreyev, P. Duppen, N. Althubiti
and 34 more authors
B. Andel, D. Atanasov, J. Billowes, K. Blaum, T. Cocolios, J. Cubiss, G. Farooq-Smith, D. Fedorov, V. Fedosseev, K. Flanagan, L. P. Ganey, L. Ghys, M. Huyse, S. Kreim, D. Lunney, K. Lynch, V. Manea, Y. M. Palenzuela, P. Molkanov, M. Rosenbusch, R. Rossel, S. Rothe, L. Schweikhard, M. Seliverstov, P. Spagnoletti, C. Beveren, M. Veinhard, E. Verstraelen, A. Welker, K. Wendt, F. Wienholtz, R. Wolf, A. Zadvornaya, K. Zuber
/ Abstract
The mean-square charge radii of $^{207,208}$Hg ($Z=80, N=127,128$) have been studied for the first time and those of $^{202,203,206}$Hg ($N=122,123,126$) remeasured by the application of in-source resonance-ionization laser spectroscopy at ISOLDE (CERN). The characteristic \textit{kink} in the charge radii at the $N=126$ neutron shell closure has been revealed, providing the first information on its behavior below the $Z=82$ proton shell closure. A theoretical analysis has been performed within relativistic Hartree-Bogoliubov and non-relativistic Hartree-Fock-Bogoliubov approaches, considering both the new mercury results and existing lead data. Contrary to previous interpretations, it is demonstrated that both the kink at $N=126$ and the odd-even staggering (OES) in its vicinity can be described predominately at the mean-field level, and that pairing does not need to play a crucial role in their origin. A new OES mechanism is suggested, related to the staggering in the occupation of the different neutron orbitals in odd- and even-$A$ nuclei, facilitated by particle-vibration coupling for odd-$A$ nuclei.