  The paper is devoted to the effects of superconducting pairing in small
metallic grains. It turns out that at strong superconducting coupling and in
the limit of large Thouless conductance one can explicitly determine the low
energy spectrum of the problem. We start with the strong coupling limit and
develop a systematic expansion in powers of the inverse coupling constant for
the many-particle spectrum of the system. The strong coupling expansion is
based on the formal exact solution of the Richardson model and converges for
realistic values of the coupling constant. We use this expansion to study the
low energy excitations of the system, in particular energy and spin gaps in the
many-body spectrum.
