Using an exact and complete Yukawa Potential Energy (YPE), the neutron-triton and neutron-helium elastic total scattering cross section is estimated and extrapolated to zero energy. The estimated value agrees pretty well with the experimental value and the procedure can be extended to any neutron-nucleus total scattering. The results are extended to the case of 4He, 7Li, 9Be and 27Al nuclei also.