Measurements and Calculations of the Neutron Spectra Emitted from Concrete Spheres Bombarded with 14-MeV Neutrons

The neutron spectra emitted from 2 and 4 mean-free-paths of concrete irradiated by 14-MeV neutrons have been measured between 14 and 2 MeV using the sphere transmission and time-of-flight techniques. The spectra have been calculated with the Monte Carlo neutron transport code TART using the ENDL Livermore neutron library and the ENDF/B-III neutron library. From the comparison between measurements and calculations, it was inferred that the nonelastic cross section for oxygen in the ENDL library was too large. A revision of the cross sections for 14- and 14.6-MeV neutrons was carried out and resulted in very good agreement between measurements and calculations.