摘要:

AbstractThe SIGMA1 (σ1) kernel broadening method is presented to Doppler broaden to any required accuracy a cross section that is described by a table of values and linear-linear interpolation in energy-cross section between tabulated values. The method is demonstrated to have no temperature or energy limitations and to be equally applicable to neutron or charged-particle cross sections. The method is qualitatively and quantitatively compared to contemporary approximate methods of Doppler broadening with particular emphasis on the effect of each approximation introduced.

ISSN:0029-5639    

DOI:10.13182/NSE76-1

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractThe total thermal-neutron cross section of natural lead under various physical conditions was measured by the transmission method. It became clear that the total cross section at room temperature previously reported is lower than the present data. The total cross section at 400, 500, and 600°C, above the melting point of lead, 327°C, was also measured, and the changes in the cross section as a function of temperature were examined, especially near and below the melting point. The data obtained for the randomly oriented polycrystalline state at room temperature were in reasonable agreement with the theoretical values calculated by the THRUSH and UNCLE-TOM codes.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26879

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractActivation cross sections for 14 (n, 2n) and 5 (n, p) reactions on xenon isotopes have been determined with 14.6-MeV neutrons using sodium perxenate and Ge(Li) gamma-ray spectroscopy. The values obtained are compared to the one earlier set of measurements on the xenon isotopes and to theoretical or empirical values. The128Xe(n,p)128I cross section is reported for the first time.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26880

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractMonte Carlo analysis of the measurements of Smith et al. of the number of fission neutrons produced per neutron absorbed,η, for 2200 m/sec neutrons absorbed by233U and235U yields:= 2.2993±0.0082 and= 2.0777±0.0064. The standard deviations include Monte Carlo, cross-section, and experimental uncertainties. The Monte Carlo analysis was confirmed by calculating measured quantities used by the experimentalists in determiningη2200.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26881

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractMonte Carlo analysis of the Oak Ridge National Laboratory measurements of the fission neutron yield due to the absorption of a 2200 m/sec neutron in233U and235U, respectively, yields:= 2.3019±0.0086 and= 2.0746±0.0078. The analysis was confirmed by calculating measured quantities employed by the experimentalists in their determinations ofη2200.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26882

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractThe effective delayed neutron fraction from fission was determined for an unreflected uranium (93.2 wt%235U) metal sphere from the ratio of time-correlated counts in a randomly pulsed neutron measurement to those in a Rossi-αmeasurement. In the randomly pulsed neutron measurements, a252Cf source was placed in the sphere which contained a fission counter that, because of its location, did not count neutrons directly from the source. Neutrons from spontaneous fission of252Cf initiated fission chains in the sphere, and the fission counter detected events from the interaction of neutrons from these fission chains with the uranium of the fission counter. A Type I time analyzer was triggered each time a252Cf nucleus fissioned and recorded the time distribution of neutrons from the fission chains initiated by neutrons from californium at t = 0. The delayed neutron fraction by this method (60.2±0.8×10−4) is∼11% lower than that from other measurements or calculations that are all in agreement. This low value may be due to an improper theoretical formulation for the correction of point kinetics for spatial effects. The value of this correction factor estimated by another theoretical formulation is 30% larger. An 11% larger correction for spatial effects would produce agreement between this measurement and previously measured results.

ISSN:0029-5639    

DOI:10.13182/NSE76-4

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractUsing a multigroup discrete-ordinate form of the transport equation, we have calculated thermal-neutron spectra along four directions at different distances from the source plane within beryllium assemblies of dimensions 35.6×35.6×50.8 cm3and 25.4×25.4×50.8 cm3. In both assemblies our calculated spectra in the forward direction at various distances from the source plane agree well with the corresponding observations of Lake and Kallfelz everywhere, except in a small energy region around 0.007 eV. We show that the increase in the proportion of cold neutrons with distance observed by them arises mainly because of the uncollided neutron flux and that the remaining distribution, i.e., the collided flux, attains pseudo-equilibrium conditions within 20 cm of the source in the larger assembly. Such equilibrium conditions are not established in the smaller assembly. We show that the conclusion drawn by Lake and Kallfelz—that their measured results contradict the earlier diffusion theory results of Ahmed et al.—is not justified. If anything, these measurements lend support to the diffusion theory results.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26884

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractContinuous neutron slowing down theory, as generalized to incorporate inelastic scattering, has been combined with integral transport theory by use of the separable kernel analogy. The result is a matrix form of continuous slowing down theory where the matrices involved are direct generalizations of the scalar quantities encountered in continuous slowing down theory. The approach has been applied to the calculation of space-dependent spectra in uranium and iron single-region problems and in two-region problems involving uranium and iron. In general, very good agreement with more precise calculations is obtained.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26885

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractThis paper presents a derivation of the conservation-law form of the single energy group transport equation in an axisymmetric toroidal coordinate system formed by rotating a nest of smooth, simply closed, plane curves of arbitrary parametric description about an axis that does not intersect the nest. This general equation can be used for generating equations specific to particular cross-section geometries or as the basis of a finite difference equation for the general case. The effect of both the toroidal and poloidal curvatures of the system are investigated, and criteria for the validity of cylindrical and planar approximations are established. The diffusion equation for this geometry is derived, and it is shown to be formally homologous to the“r-θ”cylindrical diffusion equation if the coordinate system is orthogonal and if the azimuthal coordinate,ϕ, can be ignored.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26886

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractStarting from the mechanics of collision between two perfectly elastic smooth spherical molecules, the following equation for the heat transfer rate per unit volume from a gas or vapor 2 to another gas 1 in a mixture is derived based on the kinetic theory of gases:Methods of estimating molecular diameters when experimental values are not available are indicated, and values for sodium and UO2vapor are estimated. For a set of typical values of the parameters, the time constant for the heat transfer is found to be of the order of 10−8sec, which implies that for processes occurring in time periods greater than those of the order of 10−8sec, the gases can be assumed to come to a thermal equilibrium at the instant they mix.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26887

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor