MEASUREMENTS OF 14-MEV NEUTRON MULTIPLICATION IN SPHERICAL BERYLLIUM SHELLS

New results of spherical-shell transmission measurements with 14 MeV n eutrons on pure beryllium shells up to 17 cm thick are reported. The t otal leakage neutron multiplications were measured using a Bonner sphe re system. Independently, the leakage neutron spectra were measured ov er the entire energy range, 15 MeV to thermal energies, by proton-reco il and time-of-flight methods. The total leakage multiplications are i n 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) c ross-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 leaka ge neutrons over the calculation is found for smaller beryllium thickn esses.