The isotopic behavior of the fusion cross sections and barrier curvature at energies near and below the barrier are explored using the proximity formalism. For this purpose, various versions of the proximity potentials are used to calculate the nuclear part of the interaction potential. Our study has been restricted to the isotopic systems which obey the condition of 0.5 N/Z 1.6 for their compound nuclei. The obtained results show that the barrier curvature and the fusion cross section follow a similar behavior at near- and below-barrier energies. In fact, these quantities decrease nonlinearly (second order) with the addition of a neutron. In the present study, the energy dependence of the fusion cross sections is also discussed for the considered isotopic systems.
