摘要:

AbstractRadiation scattering imaging (or density reconstruction) is viewed as an inverse problem. Using functional analysis principles, a numerical method is developed for solving this inverse problem. The method is applied for reconstructing the density distribution of a two-phase flow.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17524

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractNeutron inelastic scattering cross sections for238U levels between 680- and 1530-keV excitation energy have been measured in the incident neutron energy range from 0.9 to 2.2 MeV. The (n, n′) time-of-flight (TOF) technique was used to obtain direct differential inelastic cross sections. Neutrons were generated using the7Li(p, n)7Be reaction. Experimental parameters were optimized to achieve an energy resolution of<15 keV. Level cross sections were deduced from the measured 125-deg differential scattering cross sections. The validity of this procedure was confirmed by measuring the angular distributions for nine levels at En= 1.5 and 2.0 MeV. Background due to fission induced by fast neutrons was subtracted. The TOF spectra were unfolded using the method of the response function. The data were corrected for multiple scattering and neutron attenuation in disk scatterer geometry using an analytic method. Theoretical calculations of the cross sections were carried out using reaction models appropriate to the description of compound nucleus and direct interaction processes. The data are compared to (n, n′γ) results and the ENDF/B-V evaluation.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17525

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractA training simulator that duplicates a Savannah River Plant (SRP) reactor control room is currently under construction. Because of the complexity of the SRP reactor control and instrumentation systems, a multinode neutronics model is necesssary in order to simulate the reactor core behavior. A 240-node core model, using a semi-implicit (SI) solution technique, has been developed to fill that need. The SI model has been tested with a range of transients and is found to provide an accurate simulation with the potential of running significantly faster than real time on the reactor simulator minicomputer complex.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17526

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe emission spectra from holmium (0.8 mfp), tantalum (1 and 3 mfp), gold (1.9 mfp), and lead (1.0 mfp) have been measured using the sphere transmission and time-of-flight techniques. The 14-MeV incident neutrons are from the Lawrence Livermore National Laboratory insulated-core-transformer accelerator using the 3H(d, n)4He reaction. These materials were chosen to span a wide range of heavy nuclei, including deformed (holmium and tantalum), spherical (gold), and closed-shell (lead) nuclei. The neutron emission spectra have been measured in the 1- to 15-MeV energy interval and the results compared with Monte Carlo calculations performed using the neutron-photon transport code TART and evaluated neutron cross-section files. An alternative representation of the secondary neutron spectra has been carried out by using model calculations for precompound processes and collective effects in the calculations of the pulsed sphere emission spectra. Their importance in the quality of the agreement between measurements and calculations is discussed. The measurements are compared with the predictions of two evaluated neutron libraries, the ENDF/B-V and evaluated nuclear data library (ENDL). In addition, calculations have been carried out using neutron cross sections calculated directly from well-accepted nuclear models by the ALICE/LIVERMORE 82 and ECIS 79 codes. The quality of the agreements between the measurements and calculations obtained with the latter cross sections and those from the ENDL library is reasonably good for all the targets, and these are systematically better than the results obtained with the ENDF/B-V files. Discrepancies between measurements and calculations as great as 80% are found using the ENDF/B-V files for the emission of neutrons from gold in the 5- to 10-MeV energy range.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17527

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractIt is shown that, after integrating the transport equation over the azimuthal angle of the polar coordinates, the resulting discrete ordinates equation with respect to the polar angle is equivalent to that of the spherical haromonics method provided that the discrete ordinates were chosen as the roots of the associated Legendre functions. The form of this semi-discrete ordinates equation is independent of the order of the approximation and simpler than those of the usual spherical harmonics method. The present method may be regarded as an extension of the Wick-Chandrasekhar method to multidimensional problems, since the present equation is reduced to the second-order form of the Wick-Chandrasekhar equation in the case of one-dimensional slab geometry.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17528

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractIt is shown that the semi-discrete ordinates equation can be used to create a computer program for a general order of PLapproximations for solving the multigroup neutron transport equation in two-dimensional x-y geometry. Sample calculations for problems using up to a P7approximation and up to four energy groups are given, and the results are compared with corresponding ones obtained by the discrete ordinates method. As the order of approximations increases, both results show good agreement, when the influence of the ray effect is not appreciable. The advantage of the present method is that the ray effect does not occur, which is the problem in the discrete ordinates method.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17529

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractA closed-form solution for the angular-spatial moments of the Spencer-Lewis equation is presented that is valid for infinite homogeneous media. From the moments, the electron density distribution as a function of position and path length (energy) is reconstructed for several sample problems involving plane isotropic sources of electrons in aluminum. The results are in excellent agreement with those determined numerically using the streaming ray method.The primary use of the closed form solution will most likely be to generate accurate electron transport benchmark solutions. In principle, the electron density as a function of space, path length, and direction can be determined for planar sources of arbitrary angular distribution.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17530

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractA logical first step toward incorporating a precompound nuclear reaction theory in the Hauser-Feshbach formalism, widely used for compound reaction cross-section calculations, is to develop unified level density formulas needed for the two parts of the calculation. An advanced, simplified formulation of the spin cutoff factors for particle-hole level densities, based on the uniform pairing model, is presented. This simplified formula, explicitly dependent on the excitation energy and the exciton number, is easy to use for the precompound part of the calculation and is shown to be consistent with the formula used for the Hauser-Feshbach part of the calculation. Differences between the present approach and a previous one are analyzed.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17531

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractA procedure is described for the construction of the adjoint operator matrix in case of coupled equations defining quantities that depend on different sets of variables. This case is not properly treated in the literature. From this procedure a simple rule can be deduced for the construction of such adjoint operator matrices.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17532

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe method previously used to analyze the inelastic scattering of neutrons by238U by separating the cross sections into compound nucleus and direct interactions is applied to the corresponding data for232Th. The fission and capture channels are now included explicitly, resulting in a 5% increase in the compound nucleus contribution. Other data and theoretical techniques are discussed briefly. The excitation functions for 24 states up to 2.5 MeV are analyzed, together with two angular distributions at 2.5 MeV.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17533

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor