203 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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    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

    Measurement of the őĪ ratio and (n, ő≥) cross section of 235U from 0.2 to 200 eV at n_TOF

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    We measured the neutron capture-to-fission cross-section ratio (őĪ ratio) and the capture cross section of 235U between 0.2 and 200 eV at the n_TOF facility at CERN. The simultaneous measurement of neutron-induced capture and fission rates was performed by means of the n_TOF BaF2 Total Absorption Calorimeter (TAC), used for detection of ő≥ rays, in combination with a set of micromegas detectors used as fission tagging detectors. The energy dependence of the capture cross section was obtained with help of the 6 Li(n,t) standard reaction determining the n_TOF neutron fluence; the well-known integral of the 235U(n, f ) cross section between 7.8 and 11 eV was then used for its absolute normalization. The őĪ ratio, obtained with slightly higher statistical fluctuations, was determined directly, without need for any reference cross section. To perform the analysis of this measurement we developed a new methodology to correct the experimentally observed effect that the probabilities of detecting a fission reaction in the TAC and the micromegas detectors are not independent. The results of this work have been used in a new evaluation of 235U performed within the scope of the Collaborative International Evaluated Library Organisation (CIELO) Project, and are consistent with the ENDF/B-VIII.0 and JEFF-3.3 capture cross sections below 4 eV and above 100 eV. However, the measured capture cross section is on average 10% larger between 4 and 100 eV.This work was supported in part by the Spanish national company for radioactive waste management, ENRESA, through the CIEMAT-ENRESA agreements on ‚ÄúTransmutaci√≥n de radionucleidos de vida larga como soporte a la gesti√≥n de residuos radioactivos de alta actividad‚ÄĚ; by the Spanish Ministerio de Econom√≠a, Industria y Competitividad, through the projects FPA2014-53290-C2-1, FPA2016-76765- P, and FPA2017-82647-P; and by the European Commission 7th Framework Programme project CHANDA (Grant No. FP7-605203)

    Measurement of the őĪ ratio and (n,ő≥) cross section of U 235 from 0.2 to 200 eV at n_TOF MEASUREMENT of the őĪ RATIO and ... J. BALIBREA-CORREA et al.

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    ¬© 2020 the Author(s). Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0/). Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.We measured the neutron capture-to-fission cross-section ratio (őĪ ratio) and the capture cross section of U235 between 0.2 and 200 eV at the n_TOF facility at CERN. The simultaneous measurement of neutron-induced capture and fission rates was performed by means of the n_TOF BaF2 Total Absorption Calorimeter (TAC), used for detection of ő≥ rays, in combination with a set of micromegas detectors used as fission tagging detectors. The energy dependence of the capture cross section was obtained with help of the Li6(n,t) standard reaction determining the n_TOF neutron fluence; the well-known integral of the U235(n,f) cross section between 7.8 and 11 eV was then used for its absolute normalization. The őĪ ratio, obtained with slightly higher statistical fluctuations, was determined directly, without need for any reference cross section. To perform the analysis of this measurement we developed a new methodology to correct the experimentally observed effect that the probabilities of detecting a fission reaction in the TAC and the micromegas detectors are not independent. The results of this work have been used in a new evaluation of U235 performed within the scope of the Collaborative International Evaluated Library Organisation (CIELO) Project, and are consistent with the ENDF/B-VIII.0 and JEFF-3.3 capture cross sections below 4 eV and above 100 eV. However, the measured capture cross section is on average 10% larger between 4 and 100 eV.Peer reviewe

    Neutron spectroscopy of 26Mg states: constraining the stellar neutron sources 22Ne(a,n)25Mg

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    This work reports on accurate, high-resolution measurements of the 25Mg()26Mg and 25Mg() cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved 25Mg()26Mg parametrization. The relevant resonances for Mg were characterized from a combined R-matrix analysis of the experimental data. This resulted in an unambiguous spin/parity assignment of the corresponding excited states in 26Mg. With this information experimental upper limits of the reaction rates for 22Ne()25Mg and 22Ne()26Mg were established, potentially leading to a significantly higher ratio than previously evaluated. The impact of these results has been studied for stellar models in the mass range 2 to 25 .Funded by SCOA

    B-13,B-14(n,gamma) via Coulomb Dissociation for Nucleosynthesis towards the r-Process

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    Fracture mechanics testing of irradiated RPV steels by means of sub-sized specimens:FRACTESUS project

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    ABSTRACT: This work provides an overview of the FRACTESUS project (Euratom work programme 2019-2020). The European Union has defined clear short and long-term objectives to achieve its energy transition towards sustainable energy and a climate neutral economy by 2050. The success of this transition relies on the combination of energy efficiency and low carbon energy in all sectors of the economy. In all electricity mix scenarios up to 2050, one needs to rely on a combination of existing nuclear power plants, long-term operation, new nuclear build and future nuclear systems. The safety and operability of nuclear systems heavily rely on strategies where the integrity of structural materials plays an essential role. Due to material availability and/or irradiation constraints, the use of small sized specimens to obtain reliable measurements of the fracture resistance is needed by the nuclear industry to comply with safety directives. Measurement of fracture toughness using small-sized specimens has already been shown to be possible in both unirradiated and irradiated conditions. However, significant work is still required to achieve European regulatory acceptance. The goal of FRACTESUS is to join efforts to establish the foundation of small specimen fracture toughness validation and demonstration to address the different national regulatory authority concerns.This project is receiving funding from the Euratom work programme 2019-2020. The contributions of all partners in the FRACTESUS project are also acknowledge
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