  We give a general treatment of the spontaneous excitation rates and the
non-relativistic Lamb shift of constantly accelerated multi-level atoms as a
model for multi-level detectors. Using a covariant formulation of the dipole
coupling between the atom and the electromagnetic field we show that new
Raman-like transitions can be induced by the acceleration. Under certain
conditions these transitions can lead to stable ground and excited states which
are not affected by the non inertial motion. The magnitude of the Unruh effect
is not altered by multi-level effects. Both the spontaneous excitation rates
and the Lamb shift are not within the range of measurability.
