702 research outputs found

    Neutron-induced fission cross sections of <math><mmultiscripts><mi>Th</mi><mprescripts/><none/><mn>232</mn></mmultiscripts></math> and <math><mmultiscripts><mi mathvariant="normal">U</mi><mprescripts/><none/><mn>233</mn></mmultiscripts></math> up to 1 GeV using parallel plate avalanche counters at the CERN n_TOF facility

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    International audienceThe neutron-induced fission cross sections¬†of Th232 and U233 were measured relative to U235 in a wide neutron energy range up to 1 GeV (and from fission threshold in the case of Th232, and from 0.7¬†eV in case of U233), using the white-spectrum neutron source at the CERN Neutron Time-of-Flight (n_TOF) facility. Parallel plate avalanche counters (PPACs) were used, installed at the Experimental Area 1 (EAR1), which is located at 185¬†m from the neutron spallation target. The anisotropic emission of fission fragments were taken into account in the detection efficiency by using, in the case of U233, previous results available in EXFOR, whereas in the case of Th232 these data were obtained from our measurement, using PPACs and targets tilted 45‚ąė with respect to the neutron beam direction. Finally, the obtained results are compared with past measurements and major evaluated nuclear data libraries. Calculations using the high-energy reaction models INCL++ and ABLA07 were performed and some of their parameters were modified to reproduce the experimental results. At high energies, where no other neutron data exist, our results are compared with experimental data on proton-induced fission. Moreover, the dependence of the fission cross section¬†at 1 GeV with the fissility parameter of the target nucleus is studied by combining those (p,f) data with our (n,f) data on Th232 and U233 and on other isotopes studied earlier at n_TOF using the same experimental setup

    Neutron-induced fission cross sections of Th 232 and U 233 up to 1 GeV using parallel plate avalanche counters at the CERN n_TOF facility

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    The neutron-induced fission cross sections of 232^{232}Th and 233^{233}U were measured relative to 235^{235}U in a wide neutron energy range up to 1 GeV (and from fission threshold in the case of 232^{232}Th, and from 0.7 eV in case of 233^{233}U), using the white-spectrum neutron source at the CERN Neutron Time-of-Flight (n_TOF) facility. Parallel plate avalanche counters (PPACs) were used, installed at the Experimental Area 1 (EAR1), which is located at 185 m from the neutron spallation target. The anisotropic emission of fission fragments were taken into account in the detection efficiency by using, in the case of 233^{233}U, previous results available in EXFOR, whereas in the case of 232^{232}Th these data were obtained from our measurement, using PPACs and targets tilted 45‚ąė with respect to the neutron beam direction. Finally, the obtained results are compared with past measurements and major evaluated nuclear data libraries. Calculations using the high-energy reaction models INCL++ and ABLA07 were performed and some of their parameters were modified to reproduce the experimental results. At high energies, where no other neutron data exist, our results are compared with experimental data on proton-induced fission. Moreover, the dependence of the fission cross section at 1 GeV with the fissility parameter of the target nucleus is studied by combining those (p,f) data with our (n,f) data on 232^{232}Th and 233^{233}U and on other isotopes studied earlier at n_TOF using the same experimental setup

    Zr 92 (n,g) and (n,tot) measurements at the GELINA and n_TOF facilities

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    Neutron induced fission cross section measurements of

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    A measurement campaign to determine neutron induced fission cross sections of 240^{240}Pu and 242^{242}Pu at 2.51 and 14.83 MeV has been carried out at the 3.7 MV Van De Graaff linear accelerator at Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig. Two identical Frisch Grid fission chambers, housing back to back a 238^{238}U and a A^{A}Pu fertile sample (A = 240 or A = 242), were employed to detect the total fission yield. The neutron fluence was measured with the recoil proton telescope (T1) (Dangendorf et al. Nucl Instrum Methods Phys Res A 469:205‚Äď215, 2001), which is the German primary standard for neutron fluence measurements. The two measurements were related using a de Pangher long counter (Nolte and Thomas Metrologia 48:274‚Äď291, 2011) and the integrated beam current as monitors. The experimental results have an average uncertainty of 3‚Äď4% both at 2.51 MeV and at 14.83 MeV and have been compared to the data available in literature. The employed set-up allowed measurements of 238^{238}U ŌÉ(n,f)\sigma _{(n,f)} in parallel. The results confirm the most recent standard libraries at 2.51 and 14.83 MeV

    92^{92}Zr (n,y) and (n,tot) measurements at the GELINA and n_TOF facilities

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    Background: Stellar nucleosynthesis of elements heavier than iron is driven by neutron capture processes. 92^{92} is positioned at a strategic point along the slow nucleosynthesis path, given its proximity to the neutron magic number N=50 and its position at the matching region between the weak and main slow processes. Purpose: In parallel with recent improved astronomical data, the extraction of accurate Maxwellian averaged cross sections (MACSs) derived from a more complete and accurate set of resonance parameters should allow for a better understanding of the stellar conditions at which nucleosynthesis takes place. Methods: Transmission and capture cross section measurements using enriched 92^{92}Zr metallic samples were performed at the time-of flight facilities GELINA of JRC-Geel (BE) and n_TOF of CERN (CH). The neutron beam passing through the samples was investigated in transmission measurements at GELINA using a Li-glass scintillator. The ő≥ rays emitted during the neutron capture reactions were detected by C6_{6}D6_{6} detectors at both GELINA and n_TOF. Results: Resonance parameters of individual resonances up to 81 keV were extracted from a combined resonance shape analysis of experimental transmissions and capture yields. For the majority of the resonances the parity was determined from an analysis of the transmission data obtained with different sample thicknesses. Average resonance parameters were calculated. Conclusions: Maxwellian averaged cross sections were extracted from resonances observed up to 81 keV. The MACS for kT=30keV is fully consistent with experimental data reported in the literature. The MACSs for kT‚Č≤15keV are in good agreement with those derived from the ENDF/B-VIII.0 library and recommended in the KADoNiS database. For kT higher than 30 keV differences are observed. A comparison with MACSs obtained with the cross sections recommended in the JEFF-3.3 and JENDL 4.0 libraries shows discrepancies even for kT‚Č≤15keV

    92^{92}Zr(n,ő≥n,\gamma) and (nn,tot) measurements at the GELINA and n_TOF facilities

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    International audienceBackground: Stellar nucleosynthesis of elements heavier than iron is driven by neutron capture processes. 92Zris positioned at a strategic point along the slow nucleosynthesis path, given its proximity to the neutron magicnumber N = 50 and its position at the matching region between the weak and main slow processes.Purpose: In parallel with recent improved astronomical data, the extraction of accurate Maxwellian averagedcross sections (MACSs) derived from a more complete and accurate set of resonance parameters should allowfor a better understanding of the stellar conditions at which nucleosynthesis takes place.Methods: Transmission and capture cross section measurements using enriched 92Zr metallic samples wereperformed at the time-of flight facilities GELINA of JRC-Geel (BE) and n_TOF of CERN (CH). The neutronbeam passing through the samples was investigated in transmission measurements at GELINA using a Li-glassscintillator. The ő≥ rays emitted during the neutron capture reactions were detected by C6D6 detectors at bothGELINA and n_TOF.Results: Resonance parameters of individual resonances up to 81 keV were extracted from a combined resonanceshape analysis of experimental transmissions and capture yields. For the majority of the resonances the paritywas determined from an analysis of the transmission data obtained with different sample thicknesses. Averageresonance parameters were calculated.Conclusions: Maxwellian averaged cross sections were extracted from resonances observed up to 81 keV. TheMACS for kT = 30 keV is fully consistent with experimental data reported in the literature. The MACSs forkT¬† 15 keV are in good agreement with those derived from the ENDF/B-VIII.0 library and recommendedin the KADONIS database. For kT higher than 30 keV differences are observed. A comparison with MACSsobtained with the cross sections recommended in the JEFF-3.3 and JENDL-4.0 libraries shows discrepancieseven for kT¬† 15 keV

    Molecular dynamics simulations of Mo nanoparticles sputtering under irradiation

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    International audience99^{99}Mo is an essential isotope in nuclear medicine, but the nuclear reactors used for their production reaching their end of life, problems of supply arise and new methods of production need to be considered. Here we study the possibility of using gamma and neutron irradiation of Mo nanoparticles (NPs) in suspension and use the separation of the isotopes escaping the nanoparticle by primary recoil to evaluate the efficiency of the process for 99^{99}Mo production. Molecular Dynamics simulations with empirical potential of Ackland and Thetford were used to obtain information about the 99^{99}Mo escape yield from the NPs and the resulting sputtering depending on NPs sizes and recoil energy. Results show that the best yield is obtained for 5 nm NPs irradiated with gamma particles. These results are used to guide accelerator irradiation experiments led in parallel in order to evaluate the possibility of using accelerators instead of nuclear reactors for the production of 99^{99}Mo

    Neutron activation of 69^{69}Ga and 71^{71}Ga at kBT‚Čą25 keV

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    Background: About 50% of heavy elements are produced by the slow neutron capture process (s process) in stars. The element gallium is mostly produced during the weak s process in massive stars. Purpose: Our activation at kB_{B}T‚Čą25 keV is the first experiment in a series of activation and time-of-flight measurements on 69^{69}Ga and 71^{71}Ga relevant for astrophysics. Methods: We activated 69^{69}Ga and 71^{71}Ga with a neutron distribution that corresponds to a quasistellar distribution with kB_{B}T=25 keV at the Joint Research Centre (JRC), Geel, Belgium. Protons were provided by an electrostatic Van de Graaff accelerator to produce neutrons via the reaction 7^{7}Li(p,n). The produced activity was measured via the ő≥ emission by the decaying product nuclei by high-purity germanium detectors. Results: We provide spectrum-averaged cross sections (SACS) and ratios of the cross sections ŌÉGa_{Ga}/ŌÉAu_{Au} for the neutron spectrum of the activation. We obtain values of ŌÉ69Ga,SACS_{69Ga,SACS}=(186¬Ī12) mb and ŌÉ71GA,SACS_{71GA,SACS} = (112¬Ī7) mb, and cross section ratios of ŌÉ69Ga_{69Ga}/ŌÉAu_{Au}=0.29¬Ī0.02 and ŌÉ71Ga_{71Ga}/ŌÉAu_{Au} = 0.17¬Ī0.01. Conclusions: Our data disagree with the available evaluated data provided by KADoNiS v0.3, our cross-section ratio is about 20% higher for 69^{69}Ga and about 20% lower for 71^{71}Ga

    Measurement of 238U(n,n‚Ä≤ő≥^{238}\mathrm{U}(n,{n}^{{'}}{\gamma}) cross section data and their impact on reaction models

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    International audienceA better knowledge of (n,xn) reaction cross sections is important for both reaction modeling and energy applications. This article focuses on inelastic scattering of neutrons off 238U for which improvements are needed to better constrain evaluations and solve inconsistencies in nuclear power reactor calculations. A new precise measurement of (n,xnő≥) reaction cross sections on 238U has been performed at the GELINA (Geel Electron LINear Accelerator) neutron facility operated by EC-JRC-Geel (Belgium) with the GRAPhEME (GeRmanium array for Actinides PrEcise MEasurements) setup. The prompt ő≥-ray spectroscopy method coupled to time-of-flight measurements is used to extract (n,xnő≥) cross section values which can be further combined to infer the total neutron inelastic scattering cross section. Cross section data for 18 ő≥ transitions (five never measured before) are presented and compared to the data in the literature. Emphasis is especially given to the uncertainty determination to produce partial cross section data as accurate as possible. Due to intrinsic limitations of the experimental method, the use of additional nuclear structure information coupled with theoretical modeling is required to determine the total (n,n‚Ä≤) cross section over the whole neutron energy range. We have investigated modeling aspects of the 238U(n,n‚Ä≤ő≥) cross sections related to the description of compound nucleus and preequilibirum mechanisms as well as the discrete part of nuclear structure. Through comparison between experimental and calculated (n,n‚Ä≤ő≥) cross sections, we pinpoint inaccuracies in the description of specific reaction mechanisms and challenge recently implemented models. This helps improving the whole modeling of the (n,n‚Ä≤) reaction
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