  A new measurement of the $^{235}$U(n,f) cross section was performed at the
neutron time-of-flight facility n_TOF at CERN. The experiment focused on
neutron energies from 20 MeV to several hundred MeV, and was normalized to
neutron scattering on hydrogen. This is a measurement first of its kind at this
facility, in an energy range that was until now not often explored, so the
detector development phase was crucial for its success. Two detectors are
presented, a parallel plate fission chamber (PPFC) and a recoil proton
telescope (RPT), both dedicated to perform measurements in the incident neutron
energy range from 30 MeV to 200 MeV. The experiment was designed to minimize
statistical uncertainties in the allocated run time. Several efforts were made
to ensure that the systematic effects were understood and under control. The
results show that the detectors are suited for measurements at n_TOF above 30
MeV, and indicate the path for possible future lines of development.
