Why Do We Use Unusual Isotopes in a Meta Material?

It's unclear why you'd have normal isotopes mixed with unusual ones in this way. Though, as jesse points out, this could have to do with the properties that the isotopes have. If this was an engineered meta material, it could be that the Properties that the unusual isotopes have allow you to do something different technologically. But that brings us back to the question of why someone would want to make this weird magnesium and drop it on a beach in brazil.