Hafnium absorbs neutrons avidly and it can be used in reactor control rods. However, it is found in the same ores as zirconium, which shares the same outer electron shell configuration and thus has similar chemical properties. Their nuclear properties are profoundly different: hafnium absorbs neutrons 600 times better than zirconium. The latter, being essentially transparent to neutrons, is prized for internal reactor parts, including the metallic cladding of the fuel rods. To use these elements in their respective applications, the zirconium must be separated from the naturally co-occurring hafnium. This can be accomplished economically with ion-exchange resins.