  We consider a uniformly accelerated atom interacting with a vacuum
electromagnetic field in the presence of an infinite conducting plane boundary
and calculate separately the contributions of vacuum fluctuations and radiation
reaction to the atomic energy level shift. We analyze in detail the behavior of
the total energy shift in three different regimes of the distance in both the
low acceleration and high acceleration limits. Our results show that, in
general, an accelerated atom does not behave as if immersed in a thermal bath
at the Unruh temperature in terms of the atomic energy level shifts, and the
effect of the acceleration on the atomic energy level shifts may in principle
become appreciable in certain circumstances, although it may not be realistic
for actual experimental measurements. We also examine the effects of the
acceleration on the level shifts when the acceleration is of the order of the
transition frequency of the atom and we find some features differ from what was
obtained in the existing literature.
