The 238U fission cross section is an international standard beyond 2 MeV where the fission plateau starts. However, due to its importance in fission reactors, this cross-section should be very accurately known also in the threshold region below 2 MeV. The 238U fission cross section has been measured relative to the 235U fission cross section at CERN – n_TOF with different detection systems. These datasets have been collected and suitably combined to increase the counting statistics in the threshold region from about 300 keV up to 3 MeV. The results are compared with other experimental data, evaluated libraries, and the IAEA standards.

The 235U neutron-induced cross section is widely used as reference cross section for measuring other fission cross sections, but in the resonance region it is not considered as an IAEA standard because of the scarce experimental data covering the full region. In this work, we deal with a new analysis of the experimental data obtained with a detection setup based on parallel plate ionization chambers (PPACs) at the CERN n_TOF facility in the range from 1 eV to 10 keV. The relative cross section has been normalised to the IAEA value in the region between 7.8 and 11 eV, which is claimed as well-known. Comparison with the ENDF/B-VII evaluation and the IAEA reference file from 100 eV to 10 keV are provided.

The U238 to U235 fission cross section ratio has been determined at n_TOF up to ˜1 GeV, with two different detection systems, in different geometrical configurations. A total of four datasets has been collected and compared. They are all consistent to each other within the relative systematic uncertainty of 3–4%. The data collected at n_TOF have been suitably combined to yield a unique fission cross section ratio as a function of neutron energy. The result confirms current evaluations up to 200 MeV. Good agreement is also observed with theoretical calculations based on the INCL++/Gemini++ combination up to the highest measured energy. The n_TOF results may help solve a long-standing discrepancy between the two most important experimental datasets available so far above 20 MeV, while extending the neutron energy range for the first time up to ˜1 GeV.

The neutron-induced fission cross-section of 241Am has been measured relative to the standard fission cross-section of 235U between 0.5 and 20MeV. The experiment was performed at the CERN n_TOF facility. Fission fragments were detected by a fast ionization chamber by discriminating against the \(\alpha\)-particles from the high radioactivity of the samples. The high instantaneous neutron flux and the low background of the n_TOF facility enabled us to obtain uncertainties of \( \approx\) 5%. With the present results it was possible to resolve discrepancies between previous data sets and to confirm current evaluations, thus providing important information for design studies of future reactors with improved fuel burn-up.

The (n, gamma) reaction of the radioactive isotope Zr-93 has been measured at the n_TOF high-resolution time-of-flight facility at CERN. Resonance parameters have been extracted in the neutron energy range up to 8 keV, yielding capture widths smaller (14%) than reported in an earlier experiment. These results are important for detailed nucleosynthesis calculations and for refined studies of waste transmutation concepts. DOI: 10.1103/PhysRevC.87.014622

We have measured the neutron capture cross sections of the stable magnesium isotopes Mg-24,Mg-25,Mg-26 in the energy range of interest to the s process using the neutron time-of-flight facility n_TOF at CERN. Capture events from a natural metal sample and from samples enriched in Mg-25 and Mg-26 were recorded using the total energy method based on (C6H6)-H-2 detectors. Neutron resonance parameters were extracted by a simultaneous resonance shape analysis of the present capture data and existing transmission data on a natural isotopic sample. Maxwellian-averaged capture cross sections for the three isotopes were calculated up to thermal energies of 100 keV and their impact on s-process analyses was investigated. At 30 keV the new values of the stellar cross section for Mg-24, Mg-25, and Mg-26 are 3.8 +/- 0.2 mb, 4.1 +/- 0.6 mb, and 0.14 +/- 0.01 mb, respectively.

Neutron-induced fission cross section measurements of U-233, Am-243 and Am-241 relative to U-235 have been carried out at the neutron time-of-flight facility n_TOF at CERN. A fast ionization chamber has been employed. All samples were located in the same detector; therefore the studied elements and the reference U-235 target are subject to the same neutron beam.

The yield of the neutron capture reaction Th-232(n, gamma) has been measured at the neutron time-of-flight facility n_TOF at CERN in the energy range from 1 eV to 1 MeV. The reduction of the acquired data to the capture yield for resolved resonances from 1 eV to 4 keV is described and compared to a recent evaluated data set. The resonance parameters were used to assign an orbital momentum to each resonance. A missing level estimator was used to extract the s-wave level spacing of D-0 = 17.2 +/- 0.9 eV.

The decay from excited levels in medium and heavy nuclei can be described in a statistical approach by means of Photon Strength Functions and Level Density distributions. The study of electromagnetic cascades following neutron capture based on the use of high efficiency detectors has been shown to be well suited for probing the properties of the Photon Strength Function of heavy (high level density) and/or radioactive (high background) nuclei. In this work we have investigated for the first time the validity of the recommended PSF of actinides, in particular U-235, Np-238 and Pu-241. Our study includes the search for resonance structures in the PSF below S-n and draws conclusions regarding their existence and their characteristics in terms of energy, width and electromagnetic nature.

The neutron-induced fission cross-section of 233U has been measured at the CERN n_TOF facility relative to the standard fission cross-section of 235U between 0.5 and 20MeV. The experiment was performed with a fast ionization chamber for the detection of the fission fragments and to discriminate against \( \alpha\) -particles from the natural radioactivity of the samples. The high instantaneous flux and the low background of the n_TOF facility result in data with uncertainties of \( \approx\) 3% , which were found in good agreement with previous experiments. The high quality of the present results allows to improve the evaluation of the 233U (n,f) cross-section and, consequently, the design of energy systems based on the Th/U cycle.

Neutron-induced fission cross sections for Pb-nat and Bi-209 were measured with a white-spectrum neutron source at the CERN Neutron Time-of-Flight (n_TOF) facility. The experiment, using neutrons from threshold up to 1 GeV, provides the first results for these nuclei above 200 MeV. The cross sections were measured relative to U-235 and U-238 in a dedicated fission chamber with parallel plate avalanche counter detectors. Results are compared with previous experimental data. Upgraded parametrizations of the cross sections are presented, from threshold energy up to 1 GeV. The proposed new sets of fitting parameters improve former results along the whole energy range.

In this document, we present the final result obtained at the n_TOF experiment; for the neutron-induced fission cross section of the Np-237, from the fission threshold up to 1 GeV. The method applied to get tins result is briefly discussed. n_TOF data are compared to the last experimental measurements using other TOF facilities or the surrogate method, reported experiments performed with monoenergetic sources and the FISCAL systematic, including a discussion about the existing discrepancies.

The (n,gamma) cross section of Zr-96 has been investigated at the CERN n_TOF spallation neutron source. High-resolution time-of-flight measurements using an enriched ZrO2 sample allowed us to analyze 15 resonances below 40 keV with improved accuracy. On average, the capture widths were found to be 25% smaller than reported in earlier experiments. If complemented with the contribution by direct radiative capture, the derived Maxwellian averaged cross sections are consistent with activation data at kT = 25 keV. The present results confirm the astrophysical implications for the s-process branching at Zr-95.

The ratio of the neutron-induced fission cross-sections of 243Am and 235U was measured in the energy range from 0.5 to 20 MeV with uncertainties of ≈ 4%. The experiment was performed at the CERN n_TOF facility using a fast ionization chamber. With the good counting statistics that could be achieved thanks to the high instantaneous flux and the low backgrounds, the present results are useful for resolving discrepancies in previous data sets and are important for future reactors with improved fuel burn-up.

The CERN Neutron Time-Of-Flight (n-TOF) facility is well suited to measure small neutron-induced fission cross sections, as those of subactinides. The cross section ratios of {sup nat}Pb and {sup 209}Bi relative to {sup 235}U and {sup 238}U were measured using PPAC detectors. The fragment coincidence method allows to unambiguously identify the fission events. The present experiment provides the first results for neutron-induced fission up to 1 GeV for {sup nat}Pb and {sup 209}Bi. A good agreement with previous experimental data below 200 MeV is shown. The comparison with proton-induced fission indicates that the limiting regime where neutron-induced and proton-induced fission reach equal cross section is close to 1 GeV.

C. Lederer,1,* N. Colonna,2 C. Domingo-Pardo,3 F. Gunsing,4 F. Käppeler,5 C. Massimi,6 A. Mengoni,7,8 A. Wallner,1 U. Abbondanno,9 G. Aerts,4 H. Álvarez,10 F. Álvarez-Velarde,11 S. Andriamonje,4 J. Andrzejewski,12 P. Assimakopoulos,13,† L. Audouin,14 G. Badurek,15 M. Barbagallo,2 P. Baumann,16 F. Bečvář,17 F. Belloni,9 E. Berthoumieux,4 M. Calviani,8 F. Calviño,18 D. Cano-Ott,11 R. Capote,7,19 C. Carrapiço,20,4 A. Carrillo de Albornoz,20 P. Cennini,8 V. Chepel,21 E. Chiaveri,8 G. Cortes,22 A. Couture,23 J. Cox,23 M. Dahlfors,8 S. David,14 I. Dillmann,5 R. Dolfini,24 W. Dridi,4 I. Duran,10 C. Eleftheriadis,25 M. Embid-Segura,11 L. Ferrant,14,† A. Ferrari,8 R. Ferreira-Marques,21 L. Fitzpatrick,8 H. Frais-Koelbl,7 K. Fujii,9 W. Furman,26 I. Goncalves,21 E. González-Romero,11 A. Goverdovski,27 F. Gramegna,28 E. Griesmayer,7 C. Guerrero,11 B. Haas,29 R. Haight,30 M. Heil,31 A. Herrera-Martinez,8 M. Igashira,32 S. Isaev,14 E. Jericha,15 Y. Kadi,8 D. Karadimos,13 D. Karamanis,13 M. Kerveno,16 V. Ketlerov,26 P. Koehler,33 V. Konovalov,25 E. Kossionides,34 M. Krtička,17 C. Lampoudis,25,4 H. Leeb,15 A. Lindote,21 I. Lopes,21 R. Losito,8 M. Lozano,19 S. Lukic,16 J. Marganiec,12 L. Marques,20 S. Marrone,2 T. Martı́nez,11 P. Mastinu,28 E. Mendoza,11 P. M. Milazzo,9 C. Moreau,9 M. Mosconi,5 F. Neves,21 H. Oberhummer,15 S. O’Brien,23 M. Oshima,35 J. Pancin,4 C. Papachristodoulou,13 C. Papadopoulos,36 C. Paradela,10 N. Patronis,13 A. Pavlik,1 P. Pavlopoulos,37 L. Perrot,4 M. T. Pigni,15 R. Plag,5 A. Plompen,38 A. Plukis,4 A. Poch,22 J. Praena,19 C. Pretel,22 J. Quesada,19 T. Rauscher,39 R. Reifarth,30 M. Rosetti,40 C. Rubbia,24 G. Rudolf,16 P. Rullhusen,38 J. Salgado,20 C. Santos,20 L. Sarchiapone,8 R. Sarmento,20 I. Savvidis,25 C. Stephan,14 G. Tagliente,2 J. L. Tain,3 D. Tarrı́o,10 L. Tassan-Got,14 L. Tavora,20 R. Terlizzi,2 G. Vannini,6 P. Vaz,20 A. Ventura,40 D. Villamarin,11 V. Vlachoudis,8 R. Vlastou,36 F. Voss,5 S. Walter,5 H. Wendler,8 M. Wiescher,23 and K. Wisshak5 (n TOF Collaboration ‡ ) 1University of Vienna, Faculty of Physics, Vienna, Austria 2Istituto Nazionale di Fisica Nucleare, Bari, Italy 3Instituto de Fı́sica Corpuscular, CSIC-Universidad de Valencia, Valencia, Spain 4CEA/Saclay, IRFU, Gif-sur-Yvette, France 5Karlsruhe Institute of Technology (KIT), Campus Nord, Institut für Kernphysik, Karlsruhe, Germany 6Dipartimento di Fisica, Università di Bologna, and Sezione INFN di Bologna, Bologna, Italy 7Nuclear Data Section, International Atomic Energy Agency (IAEA), Vienna, Austria 8CERN, Geneva, Switzerland 9Istituto Nazionale di Fisica Nucleare, Trieste, Italy 10Universidade de Santiago de Compostela, Santiago de Compostela, Spain 11Centro de Investigaciones Energeticas Mediosample-independentales y Tecnologicas, Madrid, Spain 12University of Lodz, Lodz, Poland 13University of Ioannina, Ioannina, Greece 14Centre National de la Recherche Scientifique/IN2P3, IPN, Orsay, France 15Atominstitut der Österreichischen Universitäten, Technische Universität Wien, Vienna, Austria 16Centre National de la Recherche Scientifique/IN2P3, IReS, Strasbourg, France 17Charles University, Prague, Czech Republic 18Universidad Politecnica de Madrid, Madrid, Spain 19Universidad de Sevilla, Seville, Spain 20Instituto Tecnológico e Nuclear (ITN), Lisbon, Portugal 21LIP-Coimbra and Departamento de Fisica da Universidade de Coimbra, Coimbra, Portugal 22Universitat Politecnica de Catalunya, Barcelona, Spain 23University of Notre Dame, Notre Dame, Indiana 46556, USA 24Università degli Studi Pavia, Pavia, Italy 25Aristotle University of Thessaloniki, Thessaloniki, Greece 26Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna, Russia 27Institute of Physics and Power Engineering, Kaluga Region, Obninsk, Russia 28Laboratori Nazionali di Legnaro, Istituto Nazionale di Fisica Nucleare, Legnaro, Italy 29Centre National de la Recherche Scientifique/IN2P3, CENBG, Bordeaux, France 30Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA 31GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany 32Tokyo Institute of Technology, Tokyo, Japan 33Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 34NCSR, Athens, Greece 35Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki, Japan

The successful development of advanced nuclear systems for sustainable energy production and nuclear waste management depends on high quality nuclear data libraries.Recent sensitivity studies and reports [1-3] have identified the need for substantially improving the accuracy of neutron cross-section data for minor actinides.The n TOF collaboration has initiated an ambitious experimental program for the measurement of neutron capture cross sections of minor actinides.Two experimental setups have been constructed for this purpose: a Total Absorption Calorimeter (TAC) [4] for measuring neutron capture cross-sections of low-mass and/or radioactive samples and a set of two low neutron sensitivity C6D6 detectors for the less radioactive materials.

The neutron-induced fission cross section of U-236 was measured at the neutron Time-of-Flight (n_TOF) facility at CERN relative to the standard U-235(n, f) cross section for neutron energies ranging from above thermal to several MeV. The measurement, covering the full range simultaneously, was performed with a fast ionization chamber, taking advantage of the high resolution of the n_TOF spectrometer. The n_TOF results confirm that the first resonance at 5.45 eV is largely overestimated in some nuclear data libraries. The resonance triplet around 1.2 keV was measured with high resolution and resonance parameters were determined with good accuracy. Resonances at high energy have also been observed and characterized and different values for the cross section are provided for the region between 10 keV and the fission threshold. The present work indicates various shortcomings of the current nuclear data libraries in the subthreshold region and provides the basis for an accurate re-evaluation of the U-236(n, f) cross section, which is of great relevance for the development of emerging or innovative nuclear reactor technologies.

The precise determination of the neutron capture cross sections of Os-186 and Os-187 is important to define the s-process abundance of Os-187 at the formation of the solar system. This quantity can be used to evaluate the radiogenic component of the abundance of Os-187 due to the decay of the unstable Re-187 (t(1/2) = 41.2 Gyr) and from this to infer the time duration of the nucleosynthesis in our galaxy (Re/Os cosmochronometer). The neutron capture cross sections of Os-186, Os-187, and Os-188 have been measured at the CERN n_TOF facility from 1 eV to 1 MeV, covering the entire energy range of astrophysical interest. The measurement has been performed by time-of-flight technique using isotopically enriched samples and two C6D6 scintillation detectors for recording the prompt. rays emitted in the capture events. Maxwellian averaged capture cross sections have been determined for thermal energies between kT = 5 and 100 keV corresponding to all possible s-process scenarios. The estimated uncertainties for the values at 30 keV are 4.1, 3.3, and 4.7% for Os-186, Os-187, and Os-188, respectively.

The neutron-capture cross sections of Yb-168, W-180, Os-184, Pt-190, and Hg-196 have been measured by means of the activation technique. The samples were irradiated in a quasistellar neutron spectrum of kT = 25 keV, which was produced at the Karlsruhe 3.7-MV Van de Graaff accelerator via the Li-7(p, n)Be-7 reaction. Systematic uncertainties were investigated in repeated activations with different samples and by variation of the experimental parameters, that is, irradiation times, neutron fluxes, and.-ray counting conditions. The measured data were converted into Maxwellian-averaged cross sections at kT = 30 keV, yielding 1214 +/- 61, 624 +/- 54, 590 +/- 43, 511 +/- 46, and 201 +/- 11 mb for Yb-168, W-180, Os-184, Pt-190, and Hg-196, respectively. The present results either represent first experimental data (Yb-168, Os-184, and Hg-196) or could be determined with significantly reduced uncertainties (W-180 and Pt-190). These measurements are part of a systematic study of stellar (n, gamma) cross sections of the stable p isotopes.