• Question: Why can NMR only be used with atoms with an odd mass number?

    Asked by eigenvector to Arttu, Ceri, James_M, Monica, Philip on 20 Jun 2011.
    • Photo: James M Monk

      James M Monk answered on 20 Jun 2011:

      I’m guessing based on what I know about NMR, but I think it’s because it relies on being able to flip the spin of a single proton. If you had an even mass number then you could have 50% of the nuclei with their spins in one direction, 50% in the other. It’s harder in that situation to flip one of the nuclei because it would go to a higher energy state.

      If you have an odd number of nuclei then there is always one left over without a matching nuclei with spin in the other direction. So the amount of energy you need to flip its spin direction is less.

      I actually had not heard about this feature of NMR, but it makes sense when you think about it I think…

Comments