33 research outputs found
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Simultaneous evaluation of interrelated cross sections by generalized least-squares and related data file requirements
Though several cross sections have been designated as standards, they are not basic units and are interrelated by ratio measurements. Moreover, as such interactions as /sup 6/Li + n and /sup 10/B + n involve only two and three cross sections respectively, total cross section data become useful for the evaluation process. The problem can be resolved by a simultaneous evaluation of the available absolute and shape data for cross sections, ratios, sums, and average cross sections by generalized least-squares. A data file is required for such evaluation which contains the originally measured quantities and their uncertainty components. Establishing such a file is a substantial task because data were frequently reported as absolute cross sections where ratios were measured without sufficient information on which reference cross section and which normalization were utilized. Reporting of uncertainties is often missing or incomplete. The requirements for data reporting will be discussed
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Fast-neutron capture cross sections of importance in technological applications. [Review]
The importance of the capture cross section of the major fertile nuclei, /sup 238/U and /sup 232/Th, leads to the consideration of these data. The /sup 238/U (n,..gamma..) cross section is considered of priority as it is part of the /sup 238/U-/sup 239/Pu cycle. Experimental techniques used in the measurements of these data are considered. Data measured more recently are compared with provisions made for the possible explanations of differing results. It is concluded that the /sup 238/U (n,..gamma..) cross section is known with approx. 5% above 10 keV and fulfills the uncertainty limit for this cross section set to achieve design accuracy for k/sub eff/ and the breeding ratio above 500 keV. Below 500 keV, the present uncertainty falls short of the required 1.5 to 3.0% uncertainty. Specific recommendations are made to resolve existing discrepancies and data uncertainties. 84 references
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Non-destructive assay of EBR-II blanket elements using resonance transmission analysis.
Resonance transmission analysis utilizing a faltered reactor beam was examined as a means of determining the {sup 239}Pu content in Experimental Breeder Reactor-II depleted uranium blanket elements. The technique uses cadmium and gadolinium falters along with a {sup 239}Pu fission chamber to isolate the 0.3 eV resonance in {sup 239}Pu. In the energy range of this resonance (0.1 eV to 0.5 ev), the total microscopic cross-section of {sup 239}Pu is significantly greater than the cross-sections of {sup 238}U and {sup 235}U. This large difference allows small changes in the {sup 239}Pu content of a sample to result in large changes in the mass signal response. Tests with small stacks of depleted uranium and {sup 239}Pu foils indicate a significant change in response based on the {sup 239}Pu content of the foil stack. In addition, the tests indicate good agreement between the measured and predicted values of {sup 239}Pu up to approximately two weight percent
Updated Nucleosynthesis Constraints on Unstable Relic Particles
We revisit the upper limits on the abundance of unstable massive relic
particles provided by the success of Big-Bang Nucleosynthesis calculations. We
use the cosmic microwave background data to constrain the baryon-to-photon
ratio, and incorporate an extensively updated compilation of cross sections
into a new calculation of the network of reactions induced by electromagnetic
showers that create and destroy the light elements deuterium, he3, he4, li6 and
li7. We derive analytic approximations that complement and check the full
numerical calculations. Considerations of the abundances of he4 and li6 exclude
exceptional regions of parameter space that would otherwise have been permitted
by deuterium alone. We illustrate our results by applying them to massive
gravitinos. If they weigh ~100 GeV, their primordial abundance should have been
below about 10^{-13} of the total entropy. This would imply an upper limit on
the reheating temperature of a few times 10^7 GeV, which could be a potential
difficulty for some models of inflation. We discuss possible ways of evading
this problem.Comment: 40 pages LaTeX, 18 eps figure
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Data for the neutron interactions with /sup 6/Li and /sup 10/B
The /sup 10/B(n,..cap alpha..), /sup 10/B(n,..cap alpha../sub 1/) and, increasingly in more recent measurement, the /sup 6/Li(n,..cap alpha..) cross sections are the major references used in low energy experiments. Many data from modern measurements are available for the neutron interaction with /sup 6/Li, including total, scattering, and absolute and relative (n,..cap alpha..) cross sections. A consensus has been reached with these new /sup 6/Li + n data. In contrast, the data base for the /sup 10/B neutron interaction cross sections is unfortunately poor. This is even the case for the total cross section which is supposed to be the easiest quantity to be measured. The most serious deficiency is the absence of data from absolute measurements of the /sup 10/B(n,..cap alpha..) and /sup 10/B(n,..cap alpha../sub 1/) cross sections in the last 10 to 15 years. The available cross section data which were used for the ENDF/B-VI evaluation will be discussed. 43 references
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Fast neutron capture cross section measurements, evaluations and model calculations of fission product nuclei. [0. 5 to 4. 0 MeV]
The fast-neutron capture cross sections of elemental rhodium, palladium, neodymium, and samarium were measured in the energy range 0.5 to 4.0 MeV relative to the standard capture cross section of gold. A large liquid scintillator and the time-of-flight technique were used in these measurements. Experimental data are rare or non-existent in this energy range and evaluations differ substantially, with a factor of 5 being common. The present data were used together with other experimental data and nuclear model calculations in order to provide a consistent set of isotopic and elemental capture cross sections. 5 figures
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Status of nuclear data of importance for LMFBR applications prior to the evaluation of ENDF/B-VI
The evaluation of nuclear data of importance to the LMFBR program has shifted to a Nuclear Data Evaluation Task Force. It is anticipated that the results of these evaluations will be incorporated in ENDF/B-VI. However, several cross sections for reactor applications are included in a simultaneous evaluation of the standard cross sections for ENDF/B-VI organized by the Standard Subcommittee of CSEWG. Cross sections included in this simultaneous evaluation are those of /sup 6/Li(n,..cap alpha..), /sup 6/Li(n,n), /sup 10/B(n,..cap alpha../sub 0/), /sup 10/B(n,..cap alpha../sub 1/), /sup 10/B(n,n), /sup 197/Au(n,..gamma..), /sup 235/U(n,f), /sup 238/U(n,..gamma..), /sup 238/U(n,f), and /sup 239/Pu(n,f). The change of the evaluation methodology for ENDF/B-VI will result in a much improved definition of the data, their uncertainties and cross correlations. Trends which can be seen in new data and which are caused by the change of the evaluation procedure are toward, lower /sup 239/Pu(n,f), /sup 235/U(n,..gamma..), modestly lower /sup 235/U(n,f), and higher /sup 10/B(n,..cap alpha..) data. The data base for /sup 238/U(n,..gamma..) below 30 keV remains poorly defined and a resolution of the C/E discrepancy of C/sup 28//F/sup 49/ cannot be expected from the infinite dilute capture cross section of /sup 238/U. Anti nu of /sup 252/Cf remains unchanged and therefore also the nu(E) of the fissile isotopes, except at thermal energy
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Evaluation of /sup 235/U(n,f) between 100 keV and 20 MeV
The /sup 235/U(n,f) cross section is evaluated in the energy range from 100 keV to 20 MeV. Experimental data are included up to the 1978 Harwell Conference on Neutron Physics. The evaluation methodology is discussed in detail. The shape and the normalization of the cross section are evalutated in separate steps. An extensive comparison of the evaluation result with experimental data sets is made. The shape of the cross section obtained in a preliminary version of the present evaluation and a normalization factor extracted from data provided within the framework of this evaluation were used by the Subcommittee on Standards and Normalizations of the Cross Sections Evaluation Working Group to establish /sup 235/U(n,f) for ENDF/B-V above 100 keV. 20 figures, 6 tables