  We report a measurement of the cross section of single top-quark production
in the t-channel using 1.04 fb^-1 of pp collision data at sqrt(s) = 7 TeV
recorded with the ATLAS detector at the LHC. Selected events feature one
electron or muon, missing transverse momentum, and two or three jets, exactly
one of them identified as originating from a b quark. The cross section is
measured by fitting the distribution of a multivariate discriminant constructed
with a neural network, yielding sigma(t)= 83 +/- 4 (stat.) +20 -19 (syst) pb
which is in good agreement with the prediction of the Standard Model. Using the
ratio of the measured to the theoretically predicted cross section and assuming
that the top-quark-related CKM matrix elements obey the relation |V(tb)| >>
|V(ts)|, |V(td)|, the coupling strength at the W-t-b vertex is determined to be
|V(tb)| = 1.13 +0.14 -0.13. If it is assumed that |V(tb)| <= 1 a lower limit of
|V(tb)|>0.75 is obtained at the 95% confidence level.
