Abstract
The contributions of quasiparticle correlations and of continuum coupling upon the superfluid properties of neutron-rich Ni isotopes are studied within the modified BCS (MBCS) approximation at finite temperature. The effect of quasiparticle correlations is included using a secondary Bogoliubov-type canonical transformation explicitly involving the quasiparticle occupation numbers at temperature T. The effect of continuum coupling is taken into account via the finite widths of the resonant states. It is shown that the combined effect of thermal quasiparticle correlations and of continuum coupling washes out the sharp superfluid-normal phase transition given by the standard finite-temperature BCS calculations. Within the proposed resonant-continuum MBCS approximation the fluctuations of particle number also become more suppressed especially at high temperature for nuclei closer to the drip line. Finally, it is found within the same approximation that the two-neutron separation energy for ${}^{84}\mathrm{Ni}$ drops to zero at $T\ensuremath{\simeq}0.8\mathrm{MeV}.$
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