  A determination of the top-quark mass is presented using 20.2
$\text{fb}^{-1}$ of 8 TeV proton-proton collision data produced by the Large
Hadron Collider and collected by the ATLAS experiment. The normalised
differential cross section of top-quark pair production in association with an
energetic jet is measured in the lepton+jets final state and unfolded to parton
and particle levels. The unfolded distribution at parton level can be described
using next-to-leading-order QCD predictions in terms of either the top-quark
pole mass or the running mass as defined in the (modified) minimal subtraction
scheme. A comparison between the experimental distribution and the theoretical
prediction allows the top-quark mass to be extracted in the two schemes. The
value obtained for the pole-mass scheme is: \[ m_t^{\text{pole}} = 171.1 \pm
0.4 (\text{stat}) \pm 0.9 (\text{syst}) \substack{+0.7\\ -0.3} (\text{theo})
\text{ GeV}. \] The extracted value in the running-mass scheme is: \[ m_t(m_t)
= 162.9 \pm 0.5 (\text{stat}) \pm 1.0 (\text{syst}) \substack{+2.1\\ -1.2}
(\text{theo}) \text{ GeV}. \] The results for the top-quark mass using the two
schemes are consistent, when translated from one scheme to the other.
