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High resolution measurements of the angular flux spectrum of fast neutrons in CH2 were made in point-source, infinite medium and point-source, finite medium, sphere geometries. Angular flux spectra were calculated with the GGSN and GAPLSN Sn transport codes and the 05R Monte Carlo code. Comparison with experiment established that P3 anisotropic scattering and S16 angular mesh in the Sn codes were required to calculate neutron penetration to 30 cm. Results were relatively insensitive to the method of obtaining group average cross sections in the GAM-2 code, but discrepancies above 8 MeV and below 1 MeV may arise from cross section errors. The Sn code did not calculate the zero-degree flux properly and future work should include small-angle calculations with a variable-angle Sn code. The Monte Carlo results were in good agreement with comparable Sn results, but disagreed with experiment above 8 MeV. Below 1-2 MeV statistical fluctuations were large at 30 cm penetration, even for 100,000 neutron histories and with source energy biasing to reduce variance. Small-angle spectra were not calculated too well, particularly at the lower energy. However, part of this discrepancy is due to neglect of the uranium target in the 05R calculations. Recommendations are given for further investigations to resolve the remaining problems in the sphere measurements, and to extend the work to a two-dimensional geometry. (Author).
A Monte Carlo study has been made to investigate the fast-neutron spectrum and angular distribution in a large assembly of paraffin wax. The shield configuration and detector locations were chosen so that techniques currently used in calculations and experiments of neutron deep penetration could be evaluated. A modified version of the Flexible Monte Carlo (FMC) procedure, along with several data-preparation and analysis routines, was developed and used to analyze the results. Calculations were performed to determine the angular-flux values at penetration thicknesses ranging from 5 cm to 60 cm. A comparison of the calculated and measured angular flux data was made for several penetration thicknesses and angles of incidence for which experimental data were taken. A divergence in spectral shapes at 0 degree is attributed to a streaming effect in the experimental data for direct-beam flux. Except for this difference, the Monte Carlo results are in good agreement with a large range of comparable experimental results. (Author).
Measurements of the fast neutron angular flux spectrum in CH2 have been made in point-source, cylindrical geometry, using the same time-of-flight method previously applied to spherical and infinite medium geometries. This work is a continuation of the comparison of accurate, detailed, high-resolution measurements with DTF-IV discrete-ordinate and O5R Monte Carlo calculations. The sphere experiment was reanalyzed with a P16 Gauss-Legendre quadrature set in DTF-IV using the best available evaluated cross sections and P3 scattering. Reasonably good agreement was found except near 0 deg. where the discrete-ordinate code fails to calculate the very anisotropic flux. 05R calculations were made with a more complete description of the spectrum and angular distribution of the source neutrons, and included the continuum inelastic scattering, using new source generator and general inelastic scattering subroutines written for this research. Differences were small. An angular flux cylinder analysis program was written for 05R and unbiased calculations were made for the cylinder. Variance-reduction schemes are needed, however, for a meaningful comparison with the cylinder measurements. The DTF-IV code (1DF version) was put into operation on the Kirtland CDC6600 computer and the report includes input instructions. (Author).
With this book we try to reach several more-or-less unattainable goals namely: To compromise in a single book all the most important achievements of Monte Carlo calculations for solving neutron and photon transport problems. To present a book which discusses the same topics in the three levels known from the literature and gives us useful information for both beginners and experienced readers. It lists both well-established old techniques and also newest findings.