Dear Libby and Others,
Jim O'Neil once told me that we use isotope when it is modified (e.g., "the
oxygen isotope composition") but isotopic when it is not (e.g., "the
isotopic composition"). That said, people will probably strongly disagree
with this idea. We'll see what others have to say.
>A colleague from another field asked me about the correct usage of the
>terms isotope and isotopic, and with some embarrassment I had to admit
>that there is great inconsistency in our field with the use of these terms
>when used as adjectives.