  We investigate the time evolution of the decay (or ionization) probability of
a D-dimensional model atom (D=1,2,3) in the presence of a uniform (i.e., static
and homogeneous) background field. The model atom consists in a
non-relativistic point particle in the presence of a point-like attractive
well. It is shown that the model exhibits infinitely many resonances leading to
possible deviations from the naive exponential decay law of the non-decay (or
survival) probability of the initial atomic quantum state. Almost stable states
exist due to the presence of the attractive interaction, no matter how weak it
is. Analytic estimates as well as numerical evaluation of the decay rates are
explicitly given and discussed.
