  This Letter presents a search for pair production of heavy down-type quarks
decaying via b'->Wt in the lepton + jets channel, as
b'b'->WtWt->bbWWWW->lvbbqqqqqq. In addition to requiring exactly one lepton,
large missing transverse momentum and at least six jets, the invariant mass of
nearby jet pairs is used to identify high transverse momentum W bosons. In data
corresponding to an integrated luminosity of 1.04 fb^-1 from pp collisions at
sqrt(s) = 7 TeV recorded with the ATLAS detector, a heavy down-type quark with
mass less than 480 GeV is excluded at the 95% confidence level.
