Well I wasn't trying to be flippant, apologies if the first post seemed that way. Just pointing out that there are infact specific names for at least the isotopes of Hydrogen. As to the other elements, I'm not aware of any specific names for other isotopes, so C13 or K31 or whatever is what is normally seen.
KOKON, hey, it's a term/theory for a sci-fi game, it doesn't need to be perfectly logical, but none the less, certain words have certain precise meanings, and as Gorlom points out, you cannot call something with a different atomic number an isotope of another element. That's just how the word is defined.
I'd further point out that the neuclide series (actually you made it a cycle, which doesn't make sense) you provided for your scheme doesn't make any sense in the real world either, but since it's not intended for the real world it doesn't matter that much. None the less, it's almost as easy to get that kind of thing 'right' (in as much as an element with mass 300 can be right) as it is to just throw something out there.
But it really doesn't matter that much, I'm not sure how many people would care that much to learn about the nuclear properties of a made up alien element. Though that's kinda weird too, 'Alien Element'. Theory would dictate that elements are universal, so claiming that one is 'alien' is a bit of a stretch. Or just that the technology required to produce/refine/whatever this element is only available to the alien race. That would be better I guess.
If we're trying to play the 'make the sci-fi science as real as real science as we can' game.