Pairing Gap and Polarisation Effects

The phenomenological adjustment of the nuclear pairing strength is usually performed with respect to the odd-even staggering of the binding energies. We find that the results strongly depend on the way in which the ground states of the odd nuclei are computed. A thorough calculation including all time-even and time-odd polarisation effects induced by the odd nucleon produces about 30% reduced odd-even staggering as compared to the standard spherical calculations in the relativistic mean-field model. The pairing strength must be enhanced by about 20% to compensate for that effect. The enhanced strength has dramatic consequences for the predicted deformation properties of the underlying mean-field models, possibly implying that new adjustments of their parameters become necessary as well.