38 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∘ 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∘ 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

    Neutron research at the N_TOF facility (CERN): results and perspectives

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    In the first ten years of operation, the neutron time-of-flight facility n_TOF at CERN has produced a large body of new and accurate data on neutron capture and fission cross sections, relevant to Nuclear Astrophysics and advanced nuclear technologies. In the next phase, with the construction of a second experimental area with a shorted flight path, the focus of the Collaboration will partially shift from high-resolution measurements of stable or long-lived isotopes, to high-flux measurements of isotopes of relatively short half-life, very low-cross sections, or available in very small quantities. The main results obtained so far at n_TOF and the future perspectives are here presented

    Neutron capture cross section measurement of 238U{}^{238}U at the CERN n_TOF facility in the energy region from 1 eV to 700 keV

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    International audienceThe aim of this work is to provide a precise and accurate measurement of the 238U{}^{238}U(nn,Îł\gamma) reaction cross section in the energy region from 1 eV to 700 keV. This reaction is of fundamental importance for the design calculations of nuclear reactors, governing the behavior of the reactor core. In particular, fast reactors, which are experiencing a growing interest for their ability to burn radioactive waste, operate in the high energy region of the neutron spectrum. In this energy region most recent evaluations disagree due to inconsistencies in the existing measurements of up to 15%. In addition, the assessment of nuclear data uncertainty performed for innovative reactor systems shows that the uncertainty in the radiative capture cross section of 238U{}^{238}U should be further reduced to 1-3% in the energy region from 20 eV to 25 keV. To this purpose, addressed by the Nuclear Energy Agency as a priority nuclear data need, complementary experiments, one at the GELINA and two at the n_TOF facility, were proposed and carried out within the 7th Framework Project ANDES of the European Commission. The results of one of these 238U{}^{238}U(nn,Îł\gamma) measurements performed at the n_TOF CERN facility are presented in this work. The Îł\gamma-ray cascade following the radiative neutron capture has been detected exploiting a setup of two C6_6D6_6 liquid scintillators. Resonance parameters obtained from this work are on average in excellent agreement with the ones reported in evaluated libraries. In the unresolved resonance region, this work yields a cross section in agreement with evaluated libraries up to 80 keV, while for higher energies our results are significantly higher

    Integral measurement of the 12C(n, p)12B reaction up to 10 GeV

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    The integral measurement of the 12C(n, p)12B reaction was performed at the neutron time-of-flight facility n_TOF at CERN. The total number of 12B nuclei produced per neutron pulse of the n_TOF beam was determined using the activation technique in combination with a time-of-flight technique. The cross section is integrated over the n_TOF neutron energy spectrum from reaction threshold at 13.6MeV to 10GeV. Having been measured up to 1GeV on basis of the 235U(n, f) reaction, the neutron energy spectrum above 200MeV has been re-evaluated due to the recent extension of the cross section reference for this particular reaction, which is otherwise considered a standard up to 200MeV. The results from the dedicated GEANT4 simulations have been used to evaluate the neutron flux from 1GeV up to 10GeV. The experimental results related to the 12C(n, p)12B reaction are compared with the evaluated cross sections from major libraries and with the predictions of different GEANT4 models, which mostly underestimate the 12B production. On the contrary, a good reproduction of the integral cross section derived from measurements is obtained with TALYS-1.6 calculations, with optimized parameters

    Integral cross section measurement of the 12C(n,p) 12B reaction

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    The integral cross section of the 12C(n, p) 12B reaction was measured at the neutron time of flight facility n-TOF at CERN, from the reaction threshold at 13.6 MeV up to 10 GeV, by means of the combined activation and a time-offlight technique. The integral result is expressed as the number of 12B nuclei produced per single pulse of the neutron beam. A simple integral expression is given for calculating the number of produced 12B nuclei from any given evaluated cross section and/or model prediction

    Erratum: Ni 62 (n,Îł) and Ni 63 (n,Îł) cross sections measured at the n-TOF facility at CERN [Phys. Rev. C (2014) 89 (025810)]

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    C. Lederer, et al., “Erratum: 62Ni(n,Îł ) and 63Ni(n,Îł ) cross sections measured at the n_TOF facility at CERN [Phys. Rev. C 89, 025810 (2014)]”, Physical Review C, Vol. 92(1), July 2015. ©2015 American Physical Society.Peer reviewedFinal Published versio

    Experimental neutron capture data of 58Ni from the CERN n_TOF facility

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    The neutron capture cross section of 58 Ni was measured at the neutron time of flight facility n-TOF at CERN, from 27 meV to 400 keV neutron energy. Special care has been taken to identify all the possible sources of background, with the so-called neutron background obtained for the first time using high-precision GEANT4 simulations. The energy range up to 122 keV was treated as the resolved resonance region, where 51 resonances were identified and analyzed by a multilevel R-matrix code SAMMY. Above 122 keV the code SESH was used in analyzing the unresolved resonance region of the capture yield. Maxwellian averaged cross sections were calculated in the temperature range of ÎșT = 5 - 100 keV, and their astrophysical implications were investigated

    Measurement of the 240,242^{240,242}Pu(n,f) cross section at the CERN n_TOF facility

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    Knowledge of neutron cross sections of various plutonium isotopes and other minor actinides is crucial for the design of advanced nuclear systems. The 240,242^{240 , 242}Pu(n,f) cross sections were measured at the CERN n_TOF facility, taking advantage of the wide energy range (from thermal to GeV) and the high instantaneous f ux of the neutron beam. In this work, preliminary results for 242^{242}Pu are presented along with a theoretical cross section calculation performed with the EMPIRE code
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