  The upper limit of the total cross section for the pn --> pn eta' reaction
has been determined near the kinematical threshold in the excess energy range
from 0 to 24 MeV. The measurement was performed using the COSY-11 detector
setup, a deuteron cluster target, and the proton beam of COSY with a momentum
of 3.35 GeV/c. The energy dependence of the upper limit of the cross section
was extracted exploiting the Fermi momenta of nucleons inside the deuteron.
Comparison of the determined upper limit of the ratio R_eta' = sigma(pn --> pn
eta') / sigma(pp --> pp eta') with the corresponding ratio for eta-meson
production does not favor the dominance of the N*(1535) resonance in the
production process of the eta' meson and suggests nonidentical production
mechanisms for eta and eta' mesons.
