  The results of a search for direct pair production of the scalar partner to
the top quark using an integrated luminosity of $20.1 \rm{fb}^{-1}$ of
proton-proton collision data at $\sqrt{s}=8$ TeV recorded with the ATLAS
detector at the LHC are reported. The top squark is assumed to decay via
$\tilde{t} \rightarrow t \tilde{\chi}_{1}^{0}$ or $\tilde{t}\rightarrow
b\tilde{\chi}_{1}^{\pm} \rightarrow b W^{\left(\ast\right)}
\tilde{\chi}_{1}^{0}$, where $\tilde{\chi}_{1}^{0}$ ($\tilde{\chi}_{1}^{\pm}$)
denotes the lightest neutralino (chargino) in supersymmetric models. The search
targets a fully-hadronic final state in events with four or more jets and large
missing transverse momentum. No significant excess over the Standard Model
background prediction is observed, and exclusion limits are reported in terms
of the top squark and neutralino masses and as a function of the branching
fraction of $\tilde{t} \rightarrow t \tilde{\chi}_{1}^{0}$. For a branching
fraction of 100%, top squark masses in the range 270-645 GeV are excluded for
$\tilde{\chi}_{1}^{0}$ masses below 30 GeV. For a branching fraction of 50% to
either $\tilde{t} \rightarrow t \tilde{\chi}_{1}^{0}$ or $\tilde{t}\rightarrow
b\tilde{\chi}_{1}^{\pm}$, and assuming the $\tilde{\chi}_{1}^{\pm}$ mass to be
twice the $\tilde{\chi}_{1}^{0}$ mass, top squark masses in the range 250-550
GeV are excluded for $\tilde{\chi}_{1}^{0}$ masses below 60 GeV.
