1. Principle

1.1 Physical origin of the phenomenon

The interaction between the nucleus of atoms and an intense static magnetic field is studied using a resonance method: nuclear magnetic resonance. The characteristics of an atom's nucleus are based on quantum mechanics. We will explain the essential consequences as we go along. The aim of this document is not, however, to give a phenomenological description that is essentially a matter for quantum mechanics, but rather to emphasize the physical bases that are indispensable for a good understanding of the very many applications of NMR.