  The 235U(n,f) cross section was measured in a wide energy range at n_TOF
relative to 6Li(n,t) and 10B(n,alpha), with high resolution and in a wide
energy range, with a setup based on a stack of six samples and six silicon
detectors placed in the neutron beam. This allowed us to make a direct
comparison of the reaction yields under the same experimental conditions, and
taking into account the forward/backward emission asymmetry. A hint of an
anomaly in the 10{\div}30 keV neutron energy range had been previously observed
in other experiments, indicating a cross section systematically lower by
several percent relative to major evaluations. The present results indicate
that the evaluated cross section in the 9{\div}18 keV neutron energy range is
indeed overestimated, both in the recent updates of ENDF/B-VIII.0 and of the
IAEA reference data. Furthermore, these new high-resolution data confirm the
existence of resonance-like structures in the keV neutron energy region. The
new, high accuracy results here reported may lead to a reduction of the
uncertainty in the 1{\div}100 keV neutron energy region. Finally, the present
data provide additional confidence on the recently re-evaluated cross section
integral between 7.8 and 11 eV.
