Fast neutron spectrum measurements with a proton recoil spectrometer in the fast-thermal coupled critical facility STEK

Fast neutron spectrum measurements have been carried out in the STEK facility with spherical and cylindrical proton recoil counters. Spherical counters (diameter 4 cm) filled with 4 atm. H2 and 4 atm. CH4 were used in the energy range 10-800 keV and 400-1400 keV, respectively. Additional measurements were carried out in the energy range from 400-1400 keV with a cylindrical counter with 4 atm. CH4 only for the hardest and for the softest spectrum. In the energy range below 100 keV a new gamma discrimination technique, developed at ECN, was used. The measured spectrum is somewhat harder than the calculated spectrum, both in the higher energy region (without gamma discrimination) and the lower energy region. In the overlap regions the proton recoil measurements agree well with the TOF and 3He measurements