159 research outputs found

    Fission fragment angular distribution measurements of U-235 and U-238 at CERN n_TOF facility

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    Neutron-induced fission cross sections of U-238 and U-235 are used as standards in the fast neutron region up to 200 MeV. A high accuracy of the standards is relevant to experimentally determine other neutron reaction cross sections. Therefore, the detection efficiency should be corrected by using the angular distribution of the fission fragments (FFAD), which are barely known above 20 MeV. In addition, the angular distribution of the fragments produced in the fission of highly excited and deformed nuclei is an important observable to investigate the nuclear fission process. In order to measure the FFAD of neutron-induced reactions, a fission detection setup based on parallel-plate avalanche counters (PPACs) has been developed and successfully used at the CERN-n_TOF facility. In this work, we present the preliminary results on the analysis of new U-235(n,f) and U-238(n,f) data in the extended energy range up to 200 MeV compared to the existing experimental data.Postprint (published version

    Study of the 234U(n,f) fission fragment angular distribution at the CERN n_TOF facility

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    The angular distribution of the f ssion fragments (FFAD) produced in neutron induced reactions of actinides have been measured with a fission detection setup based on parallel-plate avalanche counters (PPACs) at the Neutron Time-Of-Flight (n_TOF) facility at CERN. The main features of the setup and preliminary results are reported here for the 234U(n,f) reaction measurement showing a high concordance with previous data, while providing new results up to 100 MeV.Postprint (published version

    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 Th and 233 U were measured relative to 235 U in a wide neutron energy range up to 1 GeV (and from fission threshold in the case of 232 Th , and from 0.7 eV in case of 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 U , previous results available in EXFOR, whereas in the case of 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 Th and 233 U and on other isotopes studied earlier at n_TOF using the same experimental setup.Peer ReviewedArticle escrit per 81 autors/autores: D. TarrĂ­o , L. Tassan-Got, I. Duran, L. S. Leong, C. Paradela, L. Audouin, E. Leal-Cidoncha, C. Le Naour, M. Caamaño, A. Ventura, S. Altstadt, J. Andrzejewski, M. Barbagallo, V. BĂ©cares, F. BecvĂĄ ˇ ˇr,F. Belloni, E. Berthoumieux, J. Billowes, V. Boccone, D. Bosnar, M. Brugger, M. Calviani, F. Calviño, D. Cano-Ott, C. Carrapiço, F. Cerutti, E. Chiaveri,M. Chin, N. Colonna, G. CortĂ©s, M. A. CortĂ©s-Giraldo, M. Diakaki, C. Domingo-Pardo, N. Dzysiuk, C. Eleftheriadis, A. Ferrari, K. Fraval, S. Ganesan, A. R. GarcĂ­a, G. Giubrone, M. B. GĂłmez-Hornillos, I. F. Gonçalves, E. GonzĂĄlez-Romero,E. Griesmayer, C. Guerrero, F. Gunsing, P. Gurusamy, D. G. Jenkins, E. Jericha, Y. Kadi, F. KĂ€ppeler,† D. Karadimos, P. Koehler, M. Kokkoris, M. Krticka, J. Kroll, C. Langer, C. Lederer, H. Leeb, R. Losito, A. Manousos, J. Marganiec, T. MartĂ­nez, C. Massimi, P. F. Mastinu,M. Mastromarco, M. Meaze, E. Mendoza, A. Mengoni, P. M. Milazzo, F. Mingrone, M. Mirea,,† W. Mondalaers, A. Pavlik, J. Perkowski, A. Plompen, J. Praena, J. M. Quesada, T. Rauscher, R. Reifarth, A. Riego, M. S. Robles, F. Roman, C. Rubbia, R. Sarmento, P. Schillebeeckx,S. Schmidt, G. Tagliente, J. L. Tain, A. Tsinganis, S. Valenta, G. Vannini, V. Variale, P. Vaz, R. Versaci, M. J. Vermeulen, V. Vlachoudis, R. Vlastou,A. Wallner, T. Ware, M. Weigand, C. Weiß, T. J. Wright, P. ĆœugecPostprint (published version

    The measurement programme at the neutron time-of-flight facility n-TOF at CERN

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    Neutron-induced reaction cross sections are important for a wide variety of research fields ranging from the study of nuclear level densities, nucleosynthesis to applications of nuclear technology like design, and criticality and safety assessment of existing and future nuclear reactors, radiation dosimetry, medical applications, nuclear waste transmutation, accelerator-driven systems and fuel cycle investigations. Simulations and calculations of nuclear technology applications largely rely on evaluated nuclear data libraries. The evaluations in these libraries are based both on experimental data and theoretical models. CERN's neutron time-of-flight facility n-TOF has produced a considerable amount of experimental data since it has become fully operational with the start of its scientific measurement programme in 2001. While for a long period a single measurement station (EAR1) located at 185 m from the neutron production target was available, the construction of a second beam line at 20 m (EAR2) in 2014 has substantially increased the measurement capabilities of the facility. An outline of the experimental nuclear data activities at n-TOF will be presented

    High accuracy 234U(n,f) cross section in the resonance energy region

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    New results are presented of the 234U neutron-induced fission cross section, obtained with high accuracy in the resonance region by means of two methods using the 235U(n,f) as reference. The recent evaluation of the 235U(n,f) obtained with SAMMY by L. C. Leal et al. (these Proceedings), based on previous n-TOF data [1], has been used to calculate the 234U(n,f) cross section through the 234U/235U ratio, being here compared with the results obtained by using the n-TOF neutron flux

    Neutron cross-sections for advanced nuclear systems : The n-TOF project at CERN

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    © Owned by the authors, published by EDP Sciences, 2014 This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedThe study of neutron-induced reactions is of high relevance in a wide variety of fields, ranging from stellar nucleosynthesis and fundamental nuclear physics to applications of nuclear technology. In nuclear energy, high accuracy neutron data are needed for the development of Generation IV fast reactors and accelerator driven systems, these last aimed specifically at nuclear waste incineration, as well as for research on innovative fuel cycles. In this context, a high luminosity Neutron Time Of Flight facility, n-TOF, is operating at CERN since more than a decade, with the aim of providing new, high accuracy and high resolution neutron cross-sections. Thanks to the features of the neutron beam, a rich experimental program relevant to nuclear technology has been carried out so far. The program will be further expanded in the near future, thanks in particular to a new high-flux experimental area, now under construction.Peer reviewedFinal Published versio

    238U(n, Îł) reaction cross section measurement with C 6D6 detectors at the n-TOF CERN facility

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    This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedThe radiative capture cross section of 238U is very important for the developing of new reactor technologies and the safety of existing ones. Here the preliminary results of the 238U(n,Îł) cross section measurement performed at n-TOF with C6D6 scintillation detectors are presented, paying particular attention to data reduction and background subtraction.Peer reviewe

    Cross section measurements of 155,157Gd(n, Îł) induced by thermal and epithermal neutrons

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    © SIF, Springer-Verlag GmbH Germany, part of Springer Nature 2019Neutron capture cross section measurements on 155Gd and 157Gd were performed using the time-of-flight technique at the n_TOF facility at CERN on isotopically enriched samples. The measurements were carried out in the n_TOF experimental area EAR1, at 185 m from the neutron source, with an array of 4 C6D6 liquid scintillation detectors. At a neutron kinetic energy of 0.0253 eV, capture cross sections of 62.2(2.2) and 239.8(8.4) kilobarn have been derived for 155Gd and 157Gd, respectively, with up to 6% deviation relative to values presently reported in nuclear data libraries, but consistent with those values within 1.6 standard deviations. A resonance shape analysis has been performed in the resolved resonance region up to 181 eV and 307 eV, respectively for 155Gd and 157Gd, where on average, resonance parameters have been found in good agreement with evaluations. Above these energies and up to 1 keV, the observed resonance-like structure of the cross section has been analysed and characterised. From a statistical analysis of the observed neutron resonances we deduced: neutron strength function of 2. 01 (28) × 10 - 4 and 2. 17 (41) × 10 - 4; average total radiative width of 106.8(14) meV and 101.1(20) meV and s-wave resonance spacing 1.6(2) eV and 4.8(5) eV for n + 155Gd and n + 157Gd systems, respectively.Peer reviewedFinal Accepted Versio

    The nucleosynthesis of heavy elements in Stars : The key isotope 25Mg

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    This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedWe have measured the radiative neutron-capture cross section and the total neutron-induced cross section of one of the most important isotopes for the s process, the 25Mg. The measurements have been carried out at the neutron time-of-flight facilities n-TOF at CERN (Switzerland) and GELINA installed at the EC-JRC-IRMM (Belgium). The cross sections as a function of neutron energy have been measured up to approximately 300 keV, covering the energy region of interest to the s process. The data analysis is ongoing and preliminary results show the potential relevance for the s process.Peer reviewe

    The 33S(n,α)30Si cross section measurement at n-TOF-EAR2 (CERN) : From 0.01 eV to the resonance region

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    The 33S(n,α)30Si cross section measurement, using 10B(n,α) as reference, at the n-TOF Experimental Area 2 (EAR2) facility at CERN is presented. Data from 0.01 eV to 100 keV are provided and, for the first time, the cross section is measured in the range from 0.01 eV to 10 keV. These data may be used for a future evaluation of the cross section because present evaluations exhibit large discrepancies. The 33S(n,α)30Si reaction is of interest in medical physics because of its possible use as a cooperative target to boron in Neutron Capture Therapy (NCT)
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