RELATIVISTIC MEAN FIELD PLUS BCS APPROACH TO DRIP-LINE NUCLEI

Based on a relativistic mean field (RMF) framework, we analyze the BCS approximation to the relativistic Haxtree-Bogoliubov (RHB) approach for the case of nuclei close to the drip line. In the BCS calculations the single particle continuum corresponding to RMF is replaced by a set of discrete positive energy states generated by enclosing the nucleus in a box. It is found that the main contribution to the pairing correlations for the neutron-rich nuclei is given by the low-lying resonant states, in addition to the contributions coming from the states close to the Fermi surface. Towards this end we present the results of our calculations for the entire chain of even-even Ni48-98 isotopes. Results for the neutron-rich nucleus Ni-84 is discussed in detail as a prototype. A detailed comparison of our results for the nucleus Ni-84 with those obtained in similar studies using RHB, nonrelativistic Hartree-Fock-Bogoliubov (HFB), and a recently proposed resonant continuum HF + BCS method provides strong evidence for the applicability of the RMF + BCS approach for the treatment of neutron-rich nuclei as well. Additional results of extensive calculations for the isotopes of O, Ca, Zr, Sri and Pb nuclei further reinforce our conclusions. From amongst these calculations, the results of the even-even Ca32-76 isotopes with two different RMF force parametrizations, and their agreement with the recent continuum relativistic Hartree-Bogoliubov (CRHB) results are discussed briefly for illustration purposes.