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Measurements of the fast neutron spectrum and angular distribution in a large assembly of paraffin wax (CH2) were performed. Two targets were irradiated with a pulsed electron beam from a linear accelerator, one an essentially point isotropic fission spectrum source and the other a narrow photoneutron source for small angle measurements. The time-of-flight technique was employed to measure the energy from approximately 0.3 Mev to approximately 15 Mev with an energy resolution of 10 percent. Estimated error in the spectrum is =10 percent from 0.5 to 8 Mev and =20 percent outside this range. The source spectra were measured in air for input to calculations. Data were obtained at 0 deg up to 15 cm penetration with preliminary results to 45 cm. Angular flux measurements were made up to 60 deg at 30 cm, with preliminary data at 8 deg and 45 cm. The results, within the stated accuracy and resolution, should be suitable for testing analytical techniques and corresponding shielding codes. (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).
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).
This book is based upon a series of lectures I have occasionally given at the University of Gottingen since 1951. They were meant to introduce the students of experimental physics to the work in a neutron physics laboratory dealing with the problem of measuring neutron flux, diffusion length, Fermi age, effective neutron temperature, absorption cross sections and similar problems. Moreover, these lectures were intended to prepare the students for a subsequent lecture covering the physics of nuclear reactors. The original character of this series of lectures has been retained in the book. It is intended for use by students as well as anyone desiring to work on neutron physics measurements. The first half mainly covers the theory of neutron fields, i. e. essentially diffusion and slowing down theory. The second half is largely concerned with measurements in neutron fields. The appendix contains information and data which, in our experience, are frequently required in a neutron laboratory. The field of nuclear physics proper is briefly touched upon in the first two chapters, but only to the extent necessary for the understanding of the following chapters. The multitude of applications of neutron radiation has not been covered. The conclusion of this manuscript coincided with the end of my long period of activity with the Max-Planck-Institut fur Physik at Gottingen. To Professor HEISENBERG lowe thanks for his advice and suggestions for many of the subjects treated here.