'massif' versus 'multiplet'

I tend to make the difference between a multiplet, one kind of protons for which the multiplicity is too complex to be determined and a 'massif', a range in which we have couple of different protons.

In a publication I would write:

- 12-13 (m) for a 'massif'
- 12 (m) for a 'multiplet'

However I think the term 'massif' does not really exists in english. Is there a better terminology to make the difference between those 2 cases ?