C. Paradela

Advanced nuclear energy systems and the need of accurate nuclear data: the n_TOF project at CERN

To satisfy the worlds constantly increasing demand for energy, a suitable mix of different energy sources has to be devised. In this scenario, an important role could be played by nuclear energy, provided that major safety, waste and proliferation issues affecting current nuclear reactors are satisfactorily addressed. To this purpose, a large effort has been under way for a few years towards the development of advanced nuclear systems with the aim of closing the fuel cycle. Generation IV reactors, with full or partial waste recycling capability, accelerator driven systems, as well as new fuel cycles are the main options being investigated. The design of advanced systems requires improvements in basic nuclear data, such as cross-sections for neutron-induced reactions on actinides. In this paper, the main concepts of advanced reactor systems are described, together with the related needs of new and accurate nuclear data. The present activity in this field at the neutron facility n_TOF at CERN is discussed.

Transfer reactions in inverse kinematics: An experimental approach for fission investigations

Inelastic and multinucleon transfer reactions between a U-238 beam, accelerated at 6.14 MeV/u, and a C-12 target were used for the production of neutron-rich, fissioning systems from U to Cm. A Si telescope, devoted to the detection of the targetlike nuclei, provided a characterization of the fissioning systems in atomic and mass numbers, as well as in excitation energy. Cross sections and angular and excitation-energy distributions were measured for the inelastic and transfer channels. Possible excitations of the targetlike nuclei were experimentally investigated for the first time, by means of gamma-ray measurements. The decays from the first excited states of 12C, B-11, and Be-10 were observed with probabilities of 0.12-0.14, while no evidence for the population of higher-lying states was found. Moreover, the fission probabilities of U-238, Np-239 and Pu-240,Pu-241,Pu-242 and Cm-244 were determined as a function of the excitation energy.

Neutron capture cross section of unstable 63Ni: implications for stellar nucleosynthesis.

The 63Ni(n,γ) cross section has been measured for the first time at the neutron time-of-flight facility n_TOF at CERN from thermal neutron energies up to 200 keV. In total, capture kernels of 12 (new) resonances were determined. Maxwellian averaged cross sections were calculated for thermal energies from   kT=5-100  keV with uncertainties around 20%. Stellar model calculations for a 25M⊙ star show that the new data have a significant effect on the s-process production of 63Cu, 64Ni, and 64Zn in massive stars, allowing stronger constraints on the Cu yields from explosive nucleosynthesis in the subsequent supernova.

First Measurement of Several β-Delayed Neutron Emitting Isotopes Beyond N=126

The β-delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with β-decay half-lives for 20 isotopes of Au, Hg, Tl, Pb, and Bi in the mass region N≳126. These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the β-decay strength distribution. This provides important constraints on global theoretical models currently used in r-process nucleosynthesis.

Approaching the precursor nuclei of the third r-process peak with RIBs

The rapid neutron nucleosynthesis process involves an enormous amount of very exotic neutron-rich nuclei, which represent a theoretical and experimental challenge. Two of the main decay properties that affect the final abundance distribution the most are half-lives and neutron branching ratios. Using fragmentation of a primary 238U beam at GSI we were able to measure such properties for several neutron-rich nuclei from 208Hg to 218Pb. This contribution provides a short update on the status of the data analysis of this experiment, together with a compilation of the latest results published in this mass region, both experimental and theoretical. The impact of the uncertainties connected with the eta-decay rates and with beta-delayed neutron emission is illustrated on the basis of r-process network calculations. In order to obtain a reasonable reproduction of the third r-process peak, it is expected that both half-lives and neutron branching ratios are substantially smaller, than those based on FRDM+QRPA, commonly used in r-process model calculations. Further measurements around N 126 are required for a reliable modelling of the underlying nuclear structure, and for performing more realistic r-process abundance calculations.

β -decay half-lives and β -delayed neutron emission probabilities for several isotopes of Au, Hg, Tl, Pb, and Bi, beyond N=126

R. Caballero-Folch, ∗ C. Domingo-Pardo, J. Agramunt, A. Algora, 4 F. Ameil, Y. Ayyad, J. Benlliure, M. Bowry, F. Calviño, D. Cano-Ott, G. Cortès, T. Davinson, I. Dillmann, 5, 10 A. Estrade, 11 A. Evdokimov, 10 T. Faestermann, F. Farinon, D. Galaviz, A.R. Garćıa, H. Geissel, 10 W. Gelletly, R. Gernhäuser, M.B. Gómez-Hornillos, C. Guerrero, 15 M. Heil, C. Hinke, R. Knöbel, I. Kojouharov, J. Kurcewicz, N. Kurz, Yu.A. Litvinov, L. Maier, J. Marganiec, M. Marta, 10 T. Mart́ınez, F. Montes, 18 I. Mukha, D.R. Napoli, C. Nociforo, C. Paradela, S. Pietri, Zs. Podolyák, A. Prochazka, S. Rice, A. Riego, B. Rubio, H. Schaffner, Ch. Scheidenberger, 10 K. Smith, 17, 18, 20, 21 E. Sokol, K. Steiger, B. Sun, J.L. Táın, M. Takechi, D. Testov, 23 H. Weick, E. Wilson, J.S. Winfield, R. Wood, P.J. Woods, and A. Yeremin INTE, DFEN Universitat Politècnica de Catalunya, E-08028 Barcelona, Spain TRIUMF, Vancouver, British Columbia V6T 2A3, Canada IFIC, CSIC Universitat de València, E-46071 València, Spain Institute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen H-4001, Hungary GSI Helmholtzzentrum für Schwerionenforschung GmbH, D-64291 Darmstadt, Germany Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom CIEMAT, E-28040 Madrid, Spain University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom Justus-Liebig-Universität Giessen, D-35392 Giessen, Germany St. Mary’s University, Halifax, Nova Scotia B3H 3C3, Canada Physik Department E12, Technische Universität München, D-85748 Garching, Germany Centro de F́ısica Nuclear da Universidade de Lisboa, 169-003 Lisboa, Portugal CERN Physics Department, CH-1211 Geneve, Switzerland Universidad de Sevilla, E-41080 Sevilla, Spain ExtreMe Mater Institute, D-64291 Darmstadt, Germany NSCL, Michigan State University, East Lansing, MI 48824, USA Joint Institute for Nuclear Astrophysics, Notre Dame, IN 46615, USA Instituto Nazionale di Fisica Nucleare, Laboratori Nazionale di Legnaro, I-35020 Legnaro, Italy University of Notre Dame, South Bend, IN 46556, USA University of Tennessee, Knoxville, TN 37996, USA Flerov Laboratory, Joint Institute for Nuclear Research, 141980 Dubna, Russia Institute de Physique Nucléaire d’Orsay, F-91405 Orsay, France

Structural design of an RPC-based time-of-flight wall for ions (iTOF) for the R3B-FAIR experiment

In this work we describe the mechanical design of a time-of-flight detector based on strip RPCs dedicated to measure relativistic heavy ions. The proposed design includes innovative solutions which meet the specific requirements to work with ions. The proposal is based on the results of the previous R&D program to build prototypes to test designs, materials and construction solutions, complemented by tests with relativistic ion beams. The first module of the detector has been built to be studied and characterized under beam conditions.

Performance of timing RPC detectors for relativistic ions and design of a time-of-flight detector (iToF) for the R3B-FAIR experiment for fission and spallation reactions

Resistive-plate-chambers (RPCs) were proposed to be used to build a time-of-flight detector for relativist heavy ions of the R3B-FAIR experiment, as well as other applications. State-of-the-art reaction codes allow for evaluating the requirements of the detector. The specific needs that working with heavy ions impose about material thicknesses are solved with new design concepts. We built prototypes and investigated the behaviour of RPCs tested with relativistic heavy ions. We measured the efficiency and streamer presence for ions with atomic numbers up to 38. Electron beams were used to study the timing capabilities of the prototypes.

Time resolution of small-size RPC prototypes for relativistic ions

Narrow-gap Resistive Plate Chambers (tRPCs) present excellent performances for timing with minimum ionization particles, but their performance with relativistic ions is almost unknown. We have developed small-size RPC prototypes that have been tested with electron and ion beams. The time resolution measured in both cases are below 70 ps σ, close to the challenging requirements for the R3B experiment Time-of-flight Wall at future FAIR facility.

The Neutron Time-Of-Flight Facility n_TOF At CERN: Phase II

Neutron‐induced reactions are studied at the neutron time‐of‐flight facility n_TOF at CERN. The facility uses 6∼ns wide pulses of 20 GeV/c protons impinging on a lead spallation target. The large neutron energy range and the high instantaneous neutron flux combined with high resolution are among the key characteristics of the facility. After a first phase of data taking during the period 2001–2004, the facility has been refurbished with an upgraded spallation target and cooling system for a second phase of data taking which started in 2009. Since 2010, the experimental area at 185 m where the neutron beam arrives, has been modified into a worksector of type A, allowing the extension of the physics program to include neutron‐induced reactions on radioactive isotopes.