Measurements of 14 MeV neutron multiplication in spherical beryllium shells

New results of spherical-shell transmission measurements with 14 MeV neutrons on pure beryllium shells up to 17 cm thick are reported. The total leakage neutron multiplications were measured using a Bonner sphere system. Independently, the leakage neutron spectra were measured over the entire energy range, 15 MeV to thermal energies, by proton-recoil and time-of-flight methods. The total leakage multiplications are in excellent agreement with three-dimensional Monte Carlo calculations using beryllium nuclear data based on the Young and Stewart evaluation. The leakage in the evaporation energy window confirms the Be(n,2n) cross-section of the Young and Stewart evaluation rather than that used in the ENDF/B-VI library. At energies below 1 keV, a surplus of leakage neutrons over the calculation is found for smaller beryllium thicknesses.