  We performed a measurement of differential and integral jet shapes in
proton-carbon, proton-tungsten and proton-aluminium collisions at 920 GeV/c
proton momentum with the HERA-B detector at HERA for the jet transverse
energies in the range 4 < E_T(jet) < 12 GeV. Jets were identified using the
k_T-clustering algorithm. The measurements were performed for the hardest jet
in the event, directed towards the opposite side with respect to the trigger
direction. Jets become narrower with increasing transverse energy and measured
distributions agree well with predictions of the PYTHIA 6.2 model. We do not
observe any significant difference in the jet shape for the carbon and the
aluminium targets. Nevertheless, the transverse energy flow at small and large
radii for the tungsten sample is slightly less than for light nuclei. This
observation indicates some influence of the nuclear environment on the
formation of jets in heavy nuclei, especially at lower transverse energies, 5 <
E_T(jet) < 6 GeV.
