摘要:

AbstractAn approximation method is developed which is applicable to the solving of integro-differential equations using a digital computer. This method is a generalization of the finite difference method in that information about the expected solution is added as trial solutions. This allows the possibility of significantly reducing the number of discrete mesh points necessary to achieve an accurate solution over that required by the conventional finite difference method. The method is demonstrated on some space-time reactor kinetics problems.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21166

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe space-energy synthesis approach has been improved by employing reaction rate weighting, by the use of realistic trial functions, and by deriving a more general analytical solution for the synthesis equations which includes the necessary case of complexB2.The use of reaction rates as weight functions and physically realistic trial functions made it possible to reduce the error of the space-energy synthesis method to such small values that its application in routine calculations of neutron spectra in fast reactors may be considered. The error reduction as compared to previous versions was typically a factor of 100 inδkand a factor of 20 in quantities which are sensitive to the nonseparability of space and energy. All cases with accurate results required a complexB2in the blanket region as compared to realB2for results with larger inaccuracies.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21167

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractDoppler broadening of neutron cross sections is described under the combined influence of temperature and boundary motion. The effective cross section is explicitly presented for the two cases of a constant speed, isotropic boundary motion (which is identical to the condition of an isotropic neutron flux), and also a constant speed, monodirectional boundary motion. The functional relations interconnecting the effective cross section at different temperatures and boundary motion velocities are pointed out. The results of numerical calculations are also presented.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21168

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThis paper is a sequel to the previous work on the theory and application of the multilevel formalism to Doppler effect analysis. The first part of this paper gives some quantitative results in both the resolved and the unresolved resonance regions. Detailed discussions on the interpretation and analysis of these results are given. The second part of this paper describes some further studies on the statistical behavior of theS-matrix parameters with the emphasis on the residues. Both theoretical predictions and numerical results for cases pertinent to the reactor Doppler-effect analysis are given.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21169

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe absolute ratio of fission densities due to thermal- and epicadmium-neutron fluxes has been measured by solid-state track detectors. A systematic deviation from this absolute ratio is observed when measuring gamma activities of fission products. From a careful analysis of the gamma spectra with a Ge(Li) detector, it was concluded that this systematic deviation is due to important changes in the mass distribution of fission products produced by epicadmium neutrons, with respect to the well-known mass distribution for thermal neutrons.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21170

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe object of this investigation is to obtain qualitative and quantitative understanding of reentrant hole (or extraction channel) effects in pulsed thermal- and fast-neutron experimental assemblies. The calculational model used assumes slab geometry for the unperturbed (without the hole) situation and considers cylindrical reentrant holes of various diameters and depths. The two-dimensional nature of the hole is represented by a wall-streaming term which is used as a boundary condition for a reduced effective slab. The effective slab geometry is obtained by reducing the thickness of the original slab by an amount equal to the depth of the reentrant hole. The validity of this important simplification is confirmed by results of two-dimensional discrete ordinates transport calculations in which the reentrant hole is introduced explicitly. A second basic assumption used to simplify the numerical calculations is that the flux along the walls of the reentrant hole is adequately represented by the unperturbed flux. This approximation is judged valid by the success of the method in predicting experimental results. The analytical procedure is applied numerically using discreteSntransport theory. Solutions are obtained from a code system which makes use of a standard production program DTF-IV as a subroutine for performing unperturbed and perturbed effective slab calculations. The calculational model yielded good predictions of the distorted fluxes for reentrant hole experiments performed on water at Rensselaer Polytechnic Institute. For fast neutron spectra, the model predicted distortions (particularly at high energies) which were significant but not large enough to limit the viability of the experiment.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21171

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractElastic- and inelastic-neutron-scattering cross sections of elemental Hf, Gd, and Sm were measured at incident neutron energies of 0.3 to 1.5 MeV. The experimental resolution was sufficient to reasonably resolve elastic and inelastic processes and define individual inelastic cross sections for the most appreciably excited states. The total neutron cross sections were determined up to 1.5 MeV with resolutions of≳2.5 keV. Within the precisions of the measurements all observed cross sections were relatively smooth functions of energy. The experimental results were compared with those obtained from calculations based upon both spherical and deformed optical potentials and statistical theory inclusive of fluctuation corrections. The calculated results were descriptive of measured total, elastic scattering and, to a lesser extent, inelastic scattering cross sections. Experimental and calculated results were compared with previously reported measured values and with the contents of several evaluated neutron-data sets employed in reactor design.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21172

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractExperimental measurements of the gamma-ray spectra emitted by the products of thermal-neutron fission of235U have been made at nine selected times (, 1, 2, 5, 10, 24, 48, and 72 h) after fission. A calibrated and highly collimated 5-×5-in. NaI(T1) detector was used.The 100-energy-binγ-ray spectra were unfolded from the pulse-height distributions by means of an iterative method. Extensive use was made of machine computation. The number of fissions in each sample was determined radiochemically.Significant differences between this work and calculated spectra were found. At the earlier times the experimental photon emission rate is higher than the calculated rate by as much as 40%. At later times the experimental rate is 20% lower than the calculated rate.Surprisingly large differences (as much as 33%) were found between the photon emission rates of products of fission by slow neutrons and by fast neutrons.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21173

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractBerger et al. of the National Bureau of Standards have utilized the Monte Carlo method to calculate total scatter differential dose transmission and reflection coefficients for plane unidirectional gamma rays incident on concrete barriers of finite thickness. These calculations were performed for source energies of 0.2, 0.4, 0.66, 1.25, 5.0, and 10.0 MeV with incident obliquity angles cosθ0= 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01; emergent obliquity angles cosθd= 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01; emergent azimuthal angles relative to the ongoing incident rayϕ= 0, 30, 60, 90, 120, 150, and 180 degrees; and slab thicknesses of 0.25, 0.5, 0.75, 1, 2, 3, and 4 mean-free-paths. These data are used herein to compute dose rate slant penetration and reflection probabilities for a detector located adjacent to a barrier. The total scatter contribution was calculated by numerically integrating the Monte Carlo data of Berger et al. over the 2πsolid angle subtended by the barrier relative to the detector location. In addition to results for the above listed thicknesses, energies, and incident obliquities, slant penetration and reflection probabilities are computed for the 1.12 h unfractionated fission spectrum by interpolating and weighting the Monte Carlo data at appropriate energies and thicknesses. The probabilities obtained herein compare favorably with those obtained by the Spencer-Fano moments method for an infinite medium, with other Monte Carlo studies, and with experimental data.

ISSN:0029-5639    

DOI:10.13182/NSE70-1

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE70-A21175

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor