Measured fast-neutron penetration spectra for water: comparison with calculations

Fast-neutron angular penetration spectra were experimentally determined for a fast-neutron spectrum incident on 4-, 8-, and 12-in. (102-, 203-, and 305-mm)-thick water slabs. The experimental spectra were compared with MORSE Monte Carlo calculations using readily available multigroup cross sections. The source of fast neutrons for the experimental study was the Missouri University Research Reactor; the incident and penetration neutron spectra were detected using a 2- x 2-in. (51- x 51-mm) NE-213 liquid scintillation spectrometer system. A comparison of the Monte Carlo and experimental results showed excellent agreement for all but the thickest slabs. All results showed similar trends and structure, and only for the 12-in. slab did the experimental and calculated result vary by as much as 40 percent for shallow angle penetrations. Integrated spectral results are generally within +-15 percent for all reported angles and thicknesses. A modification to the well-known MORSE code has been utilized to calculate group-to-group transfer probabilities for each of the experimental geometries. These probabilities have been converted to dose and are tabulated to permit calculation of the penetration dose for any incident neutron spectrum for the comprehensive set of angles considered in this work