Competition between pairing correlations and deformation from the odd-even mass staggering of francium and radium isotopes
Résumé
The masses of Fr-222,Fr-224,Fr-226-233 and Ra-233,Ra-234 have been determined with the Penning-trap mass spectrometer ISOLTRAP at the ISOLDE facility at CERN, including the previously unknown mass and half-life of Fr-233. We study the evolution of the odd-even staggering of binding energies along the francium and radium isotopic chains and of its lowest-order estimator, Delta(3)(N). An enhancement of the staggering of Delta(3)(N) is observed towards neutron number N = 146, which points to contributions beyond pairing correlations. These contributions are investigated in the Hartree-Fock and Hartree-Fock-Bogoliubov approaches, emphasizing the connections to the single-particle level density and nuclear deformation.