A cell in a reciprocal lattice. The first Brillouin zone is the cell of smallest volume enclosed by those planes that are perpendicular bisectors of reciprocal lattice vectors. Higher Brillouin zones also exist. Brillouin zones are used in the theory of energy levels in a periodic potential, as in a crystal. They are named after the French physicist Léon Brillouin (1889–1969), who introduced them into the theory of crystals in 1930.