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The 6Li(n,α)t reaction cross-section is an established standard due to its relatively high crosssection as well as its high Q-value. However, it is only considered a neutron standard up to 1MeV, because in the neutron energy region 1-3MeV there exist discrepancies of several per cents between recent measurements [1,2] and evaluated data files [3]. It has been speculated [4] that neglecting of the particle leaking effect might be part of the explanation why there is a disagreement in this region. Based on R-matrix calculations, in the region around 2MeV, one also expects three excitation levels of 7Li to significantly influence the cross section [5]. In order to resolve these discrepancies, we perform measurements at the GELINA facility at JRC-Geel with two Frisch-gridded ionisation chambers. The 6Li(n,α)t cross section is measured relative to the 235U(n,f) standard. In order to solve previous encountered problems [6], the setup has been modified and moved to a new flight path station. In this proceeding we show that several problems have been eliminated and discuss possible solutions to newly arisen problems, due to the changed experimental conditions. Preliminary results from new data taken during 2016 with the updated setup are presented. [ABSTRACT FROM AUTHOR]

For investigation of the basic characteristics of 14.1MeV neutron induced nuclear reactions on a number of important isotopes for nuclear science and engineering, a new experimental setup TANGRA has been constructed at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research in Dubna. For testing its performance, the angular distribution of γ -rays (and neutrons) from the inelastic scattering of 14.1MeV neutrons on high-purity carbon was measured and the angular anisotropy of γ -rays from the reaction 12C(n, n' γ)12C was determined. This reaction is important from fundamental (differential cross-sections) and practical (non-destructive elemental analysis of materials containing carbon) point of view. The preliminary results for the anisotropy of the γ -ray emission from the inelastic scattering of 14.1-MeV neutrons on carbon are compared with already published literature data. A detailed data analysis for determining the correlations between inelastic scattered neutron and γ -ray emission will be published elsewhere. [ABSTRACT FROM AUTHOR]

The 6Li(n,α) reaction cross-section is commonly used as a reference cross section. However, it is only considered a neutron standard up to 1MeV. For higher energies, there are discrepancies of several per cents between recent measurements and evaluated data files. In order to extend and establish 6Li(n,α) as a neutron standard above 1MeV these discrepancies must be resolved. Our measurement at the GELINA facility at JRC-IRMM in Geel, Belgium is ongoing. We are using a double twin Frisch-grid setup to detect both a-particles from two 6Li targets and fission products from two 235U reference targets. Our targets have thick backings but are employed in pairs, one forward facing and one backward facing. In this way we still cover, in principle, a solid angle of 4p. We present some preliminary results showing that the existing cross-section data is well reproduced around the resonance at 240 keV. The final data taking will start in the beginning of 2016, when the GELINA facility goes online again after a few months of shut down. [ABSTRACT FROM AUTHOR]

The investigation of even-odd effects in the prompt emission of even Z actinides showed a sawtooth shape of ν(Z) with staggering in the asymmetric fission region. Average prompt emission quantities as a function of A, e.g. ν(A), of even Z fragmentations are higher than those of odd Z fragmentations and they exhibit oscillations with a periodicity of about 5 mass units in the asymmetric fission region. This periodicity is not due to the Z even-odd effect in fragment distributions. The even-odd effect in <ν>(TKE) is increasing with increasing TKE and it decreases with increasing mass of the fissioning nucleus. The global even-odd effect in total average prompt emission quantities is decreasing with increasing mass of the fissioning nucleus. In the case of an even-odd fissioning nucleus, 234U(n,f), the global even-odd effect in prompt emission quantities exhibits a very slow variation with the incident neutron energy. [ABSTRACT FROM AUTHOR]

Experiments on photo-induced fission of 238U and 234U using bremsstrahlung with endpoint energies between 6 MeV and 9 MeV have been carried out at the superconducting Darmstadt electron linear accelerator S-DALINAC. A twin Frisch grid ionization chamber has been used to determine energy and mass distributions via the 2E-technique. The fission fragment emission angle, which is used to correct for energy loss in the target and backing material for a correct determination of fragment energy and mass, is deduced from the time difference between cathode and anode signals. The research program including the foreseen search for parity violation in photo-induced fission and first experimental results will be presented. [ABSTRACT FROM AUTHOR]

New, self-consistent, neutron-induced reaction cross-section calculations for 235,238U, 237Np, and 231,232,233Pa have been performed. The statistical model code STATIS was extended to take into account the multi-modality of the fission process. The three most dominant fission modes, the two asymmetric standard I (S1) and standard II (S2) modes, and the symmetric superlong (SL) mode have been taken into account. De-convoluted fission cross sections for these modes in 235,238U(n,f) and 237Np(n,f) based on experimental branching ratios, were calculated for the first time up to the second chance fission threshold. For 235U(n,f) and 233Pa(n,f), the calculations being made up to 50 MeV and 20 MeV incident neutron energy, respectively, higher fission chances have been considered. This implied the need for additional calculations for the neighbouring isotopes. As a side product also mass yield distributions could be calculated at energies hitherto not accessible by experiment. Experimental validation of the predictions is being envisaged. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The prompt fission neutron multiplicity and spectra of actinides are nuclear data of crucial importance. Based on experimental fission yield and total kinetic energy data, new calculations for the prompt neutron multiplicity and spectra for 238U(n,f), 237Np(n,f) in the incident neutron energy range up to the second chance fission threshold, for 238U(n,f), up to 50 MeV, and for 252Cf(SF) have been performed. For the first time the multi-modality of the fission process was taken into account up to the second fission chance (about 6 MeV). Additionally, for some isotopes a more realistic fission fragment residual temperature distribution as well as an anisotropy of the prompt neutron emission led to improved agreement between the calculation and experimental results. Also, the range of fission fragment pairs entering in the multiplicity and spectrum model was extended over the entire experimental fission-fragment mass range. This led to an improved version of the Los Alamos (LA) model and especially to an improved determination of the input model parameters. In addition the LA model is extended towards higher incident neutron energy, where the fission of compound nuclei formed by charged particle emission occurs. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

A method of analysis of fluctuation in the delayed neutron yield on the basis of the multimodal fission model was applied to the low-energy resolved resonances for Pu-239. The present calculation using recent data of the fluctuation of the mode branching ratios for the resolved resonances showed both positive and negative resonance structure in the delayed neutron yield relative to the thermal neutron value. This is in contrast to the U-235 case, for which mainly negative dips of about -3.5% were predicted. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The Institute for Reference Materials and Measurements (IRMM) will celebrate its 45th anniversary in 2005. With its 150-MeV Geel Electron Linear Accelerator (GELINA) and 7-MV Van de Graaff accelerator as multi-purpose neutron sources, it served the nuclear physics community for this period. The research in the field of nuclear fission was focused in recent years on both the measurement and calculation of fission cross sections, and the measurement of fission fragment properties. Fission cross sections were determined for 233Pa and 234U; the fission process was studied in the resolved resonance region of 239Pu(n,f) and for 251Cf(nth,f). These measurements derive their interest from accelerator driven systems, the thorium fuel cycle, high temperature reactors, safety issues of current reactors, and basic physics. The measurements are supported by several modeling efforts that aim at improving model codes and nuclear data evaluation. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

A report is given of the progress achieved in an IAEA Co-ordinated Research Project (CRP) to improve the cross-section standards. The objectives of the CRP, started in 2002, were initially the understanding of the origin of the strong uncertainty reduction in R-matrix model fits and the improvement of the evaluation methodology. These aims were extended in 2003 to the preparation of new evaluations for the standard 6Li(n,t), 10B(n,α), 10B(n,α1), 197Au(n,γ), 235U(n,f), and 238U(n,f) reactions. The methodology, codes, and experimental database developed by Poenitz and Hale for the ENDF/B-VI standards evaluation were taken as the basis for the new evaluation. The major results achieved by the CRP participants include the testing and intercomparison of a number of codes that can be used in the standards evaluation, updating the database of experimental results, analysis of the reasons leading to the strong uncertainty reduction in model fits, and a study of the bias in evaluated data caused by the Peelles’s Pertinent Puzzle (PPP) effect, which has been widely discussed in the nuclear data community since the ENDF/B-VI standards evaluation was completed. Preliminary results of the new standards evaluation are shown. The use of the new 235U(n,f) cross section leads to better consistency in calculations of some important integral experiments. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]