Dirac oscillator in an external magnetic field

We show that 2+1 dimensional Dirac oscillators in an external magnetic field is mapped onto the same with reduced angular frequency in absence of magnetic field. This can be used to study the atomic transitions in a radiation field. Relativistic Landau levels are constructed explicitly. Several interesting features of this system are discussed.
Revised Version, Latex, 9 pages, No figs, To appear in Phys. Lett. A