The diffusion co-efficient of Ni in Cu at 1000 K is 1.93 x 10⁻¹6⁶ m² . S⁻¹ and it is 1.94 x 10⁻¹⁴ m² S⁻¹ at 1200 K. The activation energy (in k. J.mole⁻¹ ) for the diffusion of Ni in Cu is