The excitation function and momentum distribution of eta` mesons have been measured in photon induced reactions on C-12 in the energy range of 1250-2600 MeV. The experiment was performed with tagged photon beams from the ELSA electron accelerator using the Crystal Barrel and TAPS detectors. The data are compared to model calculations to extract information on the sign and magnitude of the real part of the eta`-nucleus potential. Within the model, the comparison indicates an attractive potential of -(37 +/- 10(stat) +/- 10(syst)) MeV depth at normal nuclear matter density. Since the modulus of this depth is larger than the modulus of the imaginary part of the eta`-nucleus potential of -(10 +/- 2.5) MeV, determined by transparency ratio measurements, a search for resolved eta`-bound states appears promising. (C) 2013 Elsevier B.V. All rights reserved.