The spectral intensity of the fast-neutron flux penetrating a water medium was measured for two configurations: a large-source, poor-geometry arrangement; and a small-source, almost-good-geometry configuration., In the large-source experiment, the spectral intensity of the angular flux was obtained at six positions in the water shield of a pool-type reactor and for as many as three angles at each position. In addition to the measurements, the spectral shape and the absolute intensity of angular flux in the shield were calculated. In conjunction with this, the absolute neutron source density was mapped throughout the reactor volume and the distribution along the reactor center line was used as input to two neutron-transport calculations that were carried out for a onedimensional, spherical geometry., In the small-source experiment, a 2-cm-thick lead target irradiated with short bursts of 33-MeV electrons provided a source of photoneutrons with approximately a fission spectrum at a distance of 40 cm from water slabs of various thicknesses. This distance, together with the large separation of slab and detector and a small-aperture collimator, approximated a good-geometry arrangement for measurements of neutrons leaking normally from the slab. Consequently, these leakage spectra were very sensitive to total neutron cross sections and a distinct peak was observed at 5 to 7.5 MeV. This peak was not at first reproduced by transport calculations that used the measured source spectrum as input; however, when the neutron total cross sections of oxygen were updated with relatively recent high-resolution data, the agreement both in spectral shape and in attenuation (the latter determined from sulfur-activation ratios) was noticeably improved.
