  Theoretical results for the gaps of fractional quantum Hall states are
substantially larger than experimental values determined from the activated
behaviour of charge transport. The disparity in the case of the enigmatic nu =
5/2 state is worrying as it amounts to a factor 20 to 30. We argue that
disorder effects are responsible for this disparity and show how intrinsic gaps
can be extracted from the measured transport gaps of particle-hole symmetric
states within the same Landau level. We present new theoretical results for
gaps at nu = 5/2 and 7/2, as well as at nu = 1/3, 2/5, 3/7 and 4/9, based on
exact diagonalizations, taking account of the finite thickness of the
two-dimensional electron layer and Landau level mixing effects. We find these
to be consistent with the intrinsic gaps inferred from measured transport gaps.
While earlier analyses (Du et al, Phys. Rev. Lett. 70, 2944 (1993)) assumed
constant broadening for each sample, our results for the disorder broadening
depend on the filling fraction, and appear to scale with the charge of the
elementary excitations of the corresponding fractional state. This result is
consistent with quasiparticle mediated dissipative transport.
