  Neutron rich Ca and Ni nuclei have been studied in spherical Relativistic
Mean Field formalism in co-ordinate space. A delta interaction has been has
been adopted to treat the pairing correlations for the neutrons. Odd nuclei
have been treated in the blocking approximation. The effect of the positive
energy continuum and the role of pairing in the stability of nuclei have been
investigated using the resonant-BCS (rBCS) approach. In Ca isotopes, N=50 is no
longer a magic number while in Ni nuclei, a new magic number emerges at N=70.
There is a remarkable difference in the relative positions of the drip lines
for odd and even isotopes. In Ca isotopes, the last bound even and odd nuclei
are found to be $^{72}$Ca and $^{59}$Ca, respectively. In Ni isotopes, the
corresponding nuclei are $^{98}$Ni and $^{97}$Ni, respectively. The origin of
this difference in relative positions of the dripline in even and odd isotopes
in the two chain is traced to the difference in the single particle level
structures and consequent modification in the magic numbers in the two
elements. Pairing interaction is seen to play a major role. The effect of the
width of the resonance states on pairing has also been investigated.
