摘要:

AbstractAn analytical procedure is described for the early-time asymptotic solution of a partial-differential integral equation of the parabolic type. Several applications to the analysis of the early stages of space-dependent nuclear reactor transients are presented. The one-energy-group diffusion model with a“Newton law of cooling”linear feedback is employed. Physical interpretations of the results are given. Comparisons with results obtained by different formulations of the point-kinetic method are performed.

ISSN:0029-5639    

DOI:10.13182/NSE76-A14482

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractCurves for the reciprocal asymptotic period versus positive reactivity for ENDF/B-IV delayed neutron data are presented for232Th,233U,235U,238U,239Pu,240Pu, and241Pu nuclides. A procedure is described for reducing the dependence of reactivity interpretations, through period measurements, on the nuclidic composition of the fuel. The sensitivity of the results to incremental changes in the delayed neutron parameters is also presented. Reactivity, in dollar units, is sensitive to the relative yields of the delayed neutron groups.

ISSN:0029-5639    

DOI:10.13182/NSE76-A14483

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractValues of the ratio of the capture to fission neutron cross section,α, of235U have been determined in the energy range from 200 eV to 15 keV using a lead slowing down time spectrometer. A235U fission chamber was used to determine the fission rate, and a gamma-ray proportional counter determined both the fission and the capture rates. Both detectors were calibrated in a thermal-neutron flux using the well-known thermal energyαvalues. Neutron and gamma-ray self-shielding in the samples and background counting rates have been carefully corrected. The resultingαvalues agree well with recent time-of-flight measurements in the energy range above 0.5 keV. Below 0.5-keV neutron energy, however, large discrepancies were observed. No obvious errors in the experimental method have been found to explain thesev discrepancies.

ISSN:0029-5639    

DOI:10.13182/NSE76-A14484

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractThe neutron-induced fission cross section of237Np was measured between 3 eV and 2 MeV by the time-of-flight technique using a gas scintillator as a fission fragment detector. Two measurements were carried out with the Saclay 60-MeV Linac used as a pulsed-neutron source. The first measurement, with a nominal resolution of 2 ns/m, was performed in the 3-eV to 35-keV energy range, where the fission cross section exhibits the well-known intermediate structure. The samples were cooled to liquid nitrogen temperature to reduce the Doppler broadening predominant below 50 eV. Thanks to good statistics and to a very low background, a shape resonance analysis was possible up to 155 eV, the quoted uncertainties on the fission widths being essentially due to inaccurate neutron widths. The second experiment was run from 25 keV to 2 MeV, with a nominal resolution of 0.3 ns/m, and showed a structureless fission cross section. The agreement with the Physics 8 underground nuclear explosion data seems to be very poor in the resonance region, whereas it is more satisfactory for higher energies. Neptunium-238 fission barrier parameters were deduced from the collected data and agree fairly well with published results.

ISSN:0029-5639    

DOI:10.13182/NSE76-A14485

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractThe ENDF/B-IV prescription fails to represent correctly the238U total (and scattering) cross section between the levels of the resolved range. We show how this representation can be improved by properly accounting for the contribution of levels outside the resolved region to the cross section at energies inside the resolved region, and by substituting the more precise multi-level Breit-Wigner formula for the presently used single-level formula. We illustrate the importance of computing accurately the minima in the total cross section by comparing values of the self-shielded capture resonance integral computed with ENDF/B-IV and with a more accurate cross-section model.

ISSN:0029-5639    

DOI:10.13182/NSE76-A14486

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractAn experiment to measure the detailed energy, angular, and spatial distribution of neutrons originating from a 14-MeV neutron source in liquid air is presented. The neutron spectra are measured with a proton-recoil NE213 scintillator combined with a collimator. The measurements cover the energy range from 2 to 18 MeV at eight different angles from 0 to 90 deg. The distance between the neutron source and the measurement position varies from 60 cm (52 g/cm2) to 150 cm (130 g/cm2) in liquid air. The results are discussed and compared with known theoretical neutron transport calculations.

ISSN:0029-5639    

DOI:10.13182/NSE76-A14487

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractA fast-neutron time-of-flight spectrometer has been constructed for the purpose of measuring neutron differential cross sections of interest to the controlled thermonuclear reactor (CTR) program. The experimental facility provides the capability of measuring scattering cross sections of a few mb/sr to∼5% absolute accuracy in the energy range from 6 to 15 MeV. Source neutrons are provided by the D(d,n)3He reaction. Scattered neutrons are detected at 28 angles between 25 and 160 deg in a massively shielded NE218 liquid scintillator located 4 m from the scattering sample. Absolute cross sections are obtained by normalizing to n-p scattering. Differential elastic and inelastic scattering cross sections are reported for 8.97-, 9.19-, 9.55-, 9.96-, 10.21-, 10.69-, 10.96-, 11.16-, 11.73-, 11.96-, 12.44-, 12.95-, 13.95-, 14.43-, and 14.93- MeV neutrons incident upon high-purity carbon. Monte Carlo simulation has been used to correct for finite source and sample effects. These data partially fill the 9- to 15-MeV gap in the carbon elastic and inelastic scattering data set required for the CTR program.

ISSN:0029-5639    

DOI:10.13182/NSE76-A14488

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractA double-range spherical harmonics approximation obtained by expanding the angular flux separately in the two regions combined with the conventional single-range spherical harmonics is found to give superior description of neutron transport.

ISSN:0029-5639    

DOI:10.13182/NSE76-A14489

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractA simple scheme for solving the integral equation of neutron transport is applied to some problems in x-y geometry with reflecting boundary conditions. The present results are compared with those obtained by the use of TWOTRAN-II, both for accuracy and computational time.

ISSN:0029-5639    

DOI:10.13182/NSE76-A14490

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractCross-section ratios for production of the 0.478-MeV gamma ray by the7Li(n, n′γ)7Li reaction relative to fast-neutron fission of235U have been measured from 0.57 to 4 MeV with an estimated error of±8%. The measurements were made using a shielded Ge(Li) detector, a fission detector, and time-of-flight techniques. The measured ratios and ENDF/B-IV fission cross sections were used to compute cross sections for the7Li(n, n′γ)7Li reaction. These values are compared with corresponding reported experimental values and with the ENDF/B-IV evaluation for this reaction. The available data tend to fall into two distinct groups that disagree by as much as 25% at some energies. The results of the present work are consistent with the group that favors smaller cross sections at most energies.

ISSN:0029-5639    

DOI:10.13182/NSE76-A14491

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor