Consider solidification of manganese. The melting temperature of Mn is 1250 C, the solid-liquid interfacial energy is 0.216 Jm- and the latent heat of fusion can be approximated with Richard's rule. Nucleation at the container wall is observed to occur at 1210 C. The vibrational frequency of atoms is 101/s, the molar volume of solid Mn is 7.4 cm and the volume change during solidification is 5%. Calculate the ratio of the activation energy for heterogeneous nucleation to that for homogeneous nucleation. Determine the radius and volume of the critical nucleus.