Time Spectra from Spheres Pulsed with 14-MeV Neutrons

Neutrons emitted from pulsed spheres have been measured as a function of time in order to stringently test input parameters and computational assumptions in neutron transport calculations. Using the sphere transmission technique in conjunction with the time-of-flight facilities at Livermore, measurements have been made for 0.5, 1.3, and 3.0 mfp of carbon, and for 1.0 mfp of nitrogen, using a 15.3-MeV pulsed neutron beam. The measured neutron time spectra have proved to be sensitive, not only to the magnitude of the elastic and inelastic neutron cross sections, but also to the shapes of their angular distributions. The analysis of the data has been done using the Livermore Monte Carlo Neutron Transport Program (SORS). To obtain agreement with the data, a revision of some of the cross sections and respective angular distributions was required, which resulted in a dramatic improvement in the quality of the fits to the measured time spectra.