We show that strong pairing correlations in Fermi gases lead to the
appearance of a gap-like structure in the RF-spectrum, both in the balanced
superfluid and in the normal phase above the Clogston-Chandrasekhar limit. The
average RF-shift of a unitary gas is proportional to the ratio of the Fermi
velocity and the scattering length with the final state. In the strongly
imbalanced case, the RF-spectrum measures the binding energy of a minority atom
to the Fermi sea of majority atoms. Our results provide a qualitative
understanding of recent experiments by Schunck et.al.Comment: revised version, 4 pages, 3 figures, RevTex