  Pseudorapidity gap distributions in proton-proton collisions at sqrt(s) = 7
TeV are studied using a minimum bias data sample with an integrated luminosity
of 7.1 inverse microbarns. Cross sections are measured differentially in terms
of Delta eta F, the larger of the pseudorapidity regions extending to the
limits of the ATLAS sensitivity, at eta = +/- 4.9, in which no final state
particles are produced above a transverse momentum threshold p_T Cut. The
measurements span the region 0 < Delta eta F < 8 for 200 < p_T Cut < 800 MeV.
At small Delta eta F, the data test the reliability of hadronisation models in
describing rapidity and transverse momentum fluctuations in final state
particle production. The measurements at larger gap sizes are dominated by
contributions from the single diffractive dissociation process (pp -> Xp),
enhanced by double dissociation (pp -> XY) where the invariant mass of the
lighter of the two dissociation systems satisfies M_Y <~ 7 GeV. The resulting
cross section is d sigma / d Delta eta F ~ 1 mb for Delta eta F >~ 3. The large
rapidity gap data are used to constrain the value of the pomeron intercept
appropriate to triple Regge models of soft diffraction. The cross section
integrated over all gap sizes is compared with other LHC inelastic cross
section measurements.
