2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/192094It is shown that the chiral symmetry is spontaneously broken by a constant magnetic field in QED. The dynamical mass of fermions (energy gap in the fermion spectrum) is $m_{dyn}\simeq C\sqrt{eB}\exp\left[-\left(π/α\right) ^{1/2}\right]$, where $B$ is the magnetic field, the constant $C$ is of order one and $α=e^2/4π$ is the renormalized coupling constant. Possible applications of this effect are discussed.12 pages, LaTeX. The final journal version (with minor corrections)High Energy Physics - PhenomenologyHigh Energy Physics - Theorytext