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We study the role of the impact parameter on the collective flow and its disappearance for different mass asymmetric reactions. The mass asymmetry is varied keeping the total mass of the system fixed. Our results clearly indicate a significant role of the impact parameter on the collective flow and its disappearance for the mass asymmetric reactions. The impact parameter dependence is also found to vary with the mass asymmetry of the reaction. [ABSTRACT FROM AUTHOR]

Transmission measurements have been performed to determine the total cross section for neutron-induced reactions with 197Au in the energy region from 4keV to 108keV. The experiments were carried out at a 50m measurement station of the time-of-flight facility GELINA using a 6Li glass scintillator. The average total cross section as a function of neutron energy was derived after correcting the observed average transmission for cross section fluctuations due to resonance structures. The results have been compared with literature data and with the total cross section resulting from a dispersive coupled-channel optical model potential. The neutron strength function for s -wave neutrons and an orbital-independent scattering radius, together with their covariance matrix, have been derived in the neutron energy region between 4keV and 108keV through a parameterization of the total cross section based on a nuclear reaction theory. [ABSTRACT FROM AUTHOR]

Gamma-ray transitions following neutron capture in 206Pb have been studied at the cold neutron beam facility of the Budapest Neutron Centre using a metallic sample enriched in 206Pb and a natural lead nitrate powder pellet. The measurements were performed using a coaxial HPGe detector with Compton suppression. The observed $ \gamma$ -rays have been incorporated into a decay scheme for neutron capture in 206Pb . Partial capture cross sections for 206Pb(n, $ \gamma$ ) at thermal energy have been derived relative to the cross section for the 1884keV transition after neutron capture in 14N . From the average crossing sum a total thermal neutron capture cross section of $ 29^{+2}_{-1}$ mb was derived for the 206Pb(n, $ \gamma$ ) reaction. The thermal neutron capture cross section for 206Pb has been compared with contributions due to both direct capture and distant unbound s-wave resonances. From the same measurements a thermal neutron-induced capture cross section of $ (649 \pm 14)$ mb was determined for the 207Pb(n, $ \gamma$ ) reaction. [ABSTRACT FROM AUTHOR]

The k-literature has been reviewed every decade but some of its nuclear data is still more than 30 years old. Sometimes Q values were adopted from the nuclear data at that time or were experimentally determined by only 1 laboratory. Other isotopes were listed with accurate pairs of ( k, Q) values but were also quoted as candidates for redetermination for different reasons (i.e. imprecise cadmium transmission factors, half-lives). In this work we aim at the experimental re-determination of k and Q values for 41 isotopes of analytical interest while introducing a methodology for simultaneous $$ \bar{E}_{r} $$ and Q determination employing N irradiation channels. In order to satisfy the metrological level required, up to 12 repeats per standard were irradiated in up to 4 irradiation channels of the Belgian Reactor 1 (BR1, SCK∙CEN) having a wide spread in neutron characteristics. Our relative percentile differences to the literature values were usually ≤10 % for Q factors, ≥25 % for $$ \bar{E}_{r} $$ values and ≤4 % for k values. Our precision and accuracy are discussed thoroughly. [ABSTRACT FROM AUTHOR]

Abstract: Recent advancements in computer technology have led to an increased ability to solve complicated reactor problems, and as a result, there has been an interest in codes and methods that utilize whole-core transport in three-dimensional, large-scale, highly-heterogeneous configurations. Most current reactor benchmark problems are either small-scale or involve spatial homogenization (pin cell or full-assembly) for diffusion codes; therefore, new whole-core benchmark problems must be designed in order to validate whole-core transport methods. This study focuses on an PWR case, with a low leakage loading pattern and Gadolinium as a burnable absorber. In this paper, a detailed description of a new 3D whole-core numerical benchmark problem based on a 4-loop layout is presented with geometric, material and cross section specifications. A set of 2-group and 4-group region-wise neutron cross section libraries is generated using the lattice depletion code HELIOS, and an MCNP model is described for three configurations (all rods in, all rods out, power-shaping rods inserted). Eigenvalues are presented for the 2-group calculations of all three configurations, and detailed pin fission density results are presented for the power-shaping configuration. [Copyright &y& Elsevier]

Neutron cross section standards are the basis for the determination of most neutron cross sections. They are used for both measurements and evaluations of neutron cross sections. Not many cross sections can be obtained absolutely – most cross sections are measured relative to the cross section standards and converted using evaluations of the standards. The previous complete evaluation of the neutron cross section standards was finished in 1987 and disseminated as the NEANDC/INDC and ENDF/B-VI standards. R-matrix model fits for the light elements and non-model least-squares fits for all the cross sections in the evaluation were the basis of the combined fits for all of the data. Some important reactions and constants are not standards, but they assist greatly in the determination of the standard cross sections and reduce their uncertainties – these data were also included in the combined fits. The largest experimental database used in the evaluation was prepared by Poenitz and included about 400 sets of experimental data with covariance matrices of uncertainties that account for all cross-energy, cross-reaction and cross-material correlations. For the evaluation GMA, a least-squares code developed by Poenitz, was used to fit all types of cross sections (absolute and shape), their ratios, spectrum-averaged cross sections and thermal constants in one full analysis. But, the uncertainties derived in this manner, and especially those obtained in the R-matrix model fits, have been judged to be too low and unrealistic. These uncertainties were substantially increased prior to their release in the recommended data files of 1987. Modified percentage uncertainties were reassigned by the United States Cross Section Evaluation Working Group''s Standards Subcommittee for a wide range of energies, and no covariance (or correlation) matrices were supplied at that time. The need to re-evaluate the cross section standards is based on the appearance of a significant amount of precise experimental data and improved developments in the methodology of analysis and evaluation. Initial efforts to produce a new evaluation were made by the United States Cross Section Evaluation Working Group which formed a Task Force. It was realized that international cooperation would be needed to produce the evaluation. The Working Party on International Evaluation Cooperation of the Nuclear Energy Agency Nuclear Science Committee formed a Subgroup, and the International Atomic Energy Agency formed a Coordinated Research Project (CRP). These groups worked cooperatively to improve the evaluation process. The major effort in producing the evaluation was through the CRP. The evaluations of the neutron cross section standards were finalized in October 2005. Previous difficulties experienced with a data evaluation problem known as “Peelle''s Pertinent Puzzle” create biases in the fit of correlated data, and they have been addressed to reduce this phenomenon. The new evaluations of the cross section standards also include covariance matrices of the uncertainties that contain fully justifiable values. The product of this international effort has been adopted as the neutron standards for ENDF/B-VII.0. [Copyright &y& Elsevier]

New measurements and an improved evaluation process were used to obtain a new evaluation of the neutron cross section standards. Efforts were made to include as much information as possible on the components of the data uncertainties that were then used to obtain the covariance matrices for the experimental data. Evaluations were produced from this process for the 6Li(n,t), 10B(n,α), 10B(n,), 197Au(n,γ), 235U(n,f), and 238U(n,f) standard cross sections as well as the non-standard 6Li(n,n), 10B(n,n), 238U(n,γ) and 239Pu(n,f) cross sections. There is a general increase in the cross sections for most of the new evaluations, by as much as about 5%, compared with the ENDF/B-VI results. Covariance data were obtained for the 6Li(n,t), 6Li(n,n), 10B(n,α), 10B(n,), 10B(n,n), 197Au(n,γ), 235U(n,f), 238U(n,f), 238U(n,γ) and 239Pu(n,f) reactions. Also an independent R-Matrix evaluation was produced for the H(n,n) standard cross-section, however, covariance data are not available for this reaction. The evaluations were used in the new ENDF/B-VII library. [Copyright &y& Elsevier]

Abstract: The differential cross section has been measured with the ANKE spectrometer at COSY–Jülich for pion cms angles between 0° and 15.4° at a proton beam energy of 0.8 GeV. The selection of diproton pairs with an excitation energy ensures that the final pp system is dominantly in the spin-singlet state. The kinematics are therefore very similar to those of but with different spin and isospin transitions. The cross sections are over two orders of magnitude smaller than those of and show a forward dip that is even stronger than that seen at lower energies. The results should provide a crucial extra test of pion production models in nucleon–nucleon collisions. [Copyright &y& Elsevier]