Neutron capture cross section measurements of 238U, 241Am and 243Am at n_TOF

Proposal: Neutron capture cross section measurements of 238U, 241Am and 243Am at n_TOFThe increase of the world energy demand and the need of low carbon energy sources have triggered the renaissance and/or enhancement of nuclear energy in many countries. Fundamental nuclear physics can contribute in a practical way to the sustainability and safety of the nuclear energy production and the management of the nuclear waste. There exists a series of recent studies which address the most relevant isotopes, decay data, nuclear reaction channels and energy ranges which have to be investigated in more detail for improving the design of different advanced nuclear systems [1] and nuclear fuel cycles [2]. In this proposal, we aim at the measurement of the neutron capture cross sections of 238U, 241Am and 243Am. All three isotopes are listed in the NEA High Priority Request List [37], are recommended for measurements [1] and play an important role in the nuclear energy production and fuel cycle scenarios. The measurements will provide as well valuable nuclear structure data necessary for the improvement of nuclear models and the statistical interpretation of the nuclear propertiesPostprint (author's final draft

Radiative capture on 242Pu for MOX fuel reactors

Proposal: Radiative capture on 242Pu for MOX fuel reactorsThe use of MOX fuel (mixed-oxide fuel made of UO2 and PuO2) in nuclear reactors allows substituting a large fraction of the enriched Uranium by Plutonium reprocessed from spent fuel. Indeed around 66% of the plutonium from spent fuel is made of 239Pu and 241Pu, which are fissile in thermal reactors. A typical reactor of this type uses a fuel with 7% reprocessed Pu and 93% depleted U, thus profiting from both the spent fuel and the remaining 238U following the 235U enrichment. With the use of such new fuel compositions rich in Pu the better knowledge of the capture and fission cross sections of the Pu isotopes becomes very important. This is clearly stated in the recent OECD NEA’s “High Priority Request List” and in the WPEC-26 “Uncertainty and target accuracy assessment for innovative systems using recent covariance data evaluations” report. In particular, a new series of cross section evaluations have been recently carried out jointly by the European (JEFF) and United States (ENDF) nuclear data agencies. As the new evaluations on 240Pu and 241Am have been already completed, 242Pu is the next to be reevaluated, and the scarceness of capture data (only two TOF measurements from 1973 and 1976 are available and disagree with each other) calls for a new time-of flight capture cross section measurement. This will be the first measurement in 40 years and, with the use of more advanced techniques, shall provide a more reliable and accurate result. We propose to measure the capture cross section of 242Pu in the region from thermal up to at least 60 keV, aiming for a high energy limit of 500 keV. The experiment would make use of an array of 4 low neutron sensitivity C6D6 detectors and be carried out at the n_TOF EAR-1 (185 m flight path) measuring station. Compared to the current uncertainty of 35%, this measurement aims at an improved accuracy between 7% and 12% depending on the energy region.Preprin

Neutron capture on ^{205}Tl: depicting the abundance pattern of lead isotopes in s-process nucleosynthesis

Proposal: Neutron capture on 205Tl: depicting the abundance pattern of lead isotopes in s-process nucleosynthesisWe propose to use the TOF technique to measure the neutron capture cross section of 205Tl(n,gamma) over the full energy range of stellar interest. An accurate measurement of this cross section is needed for a complete and consistent understanding of the s-process nucleosynthesis of the heaviest nuclei which are produced in low-mass and low metallicity AGB-stars. The only previous TOF measurement has yield only a partial information, insufficient for a reliable analysis of the complex branching pattern around 205Pb and 205Tl. Furthermore, there is also a discrepancy of 40% between the two previous activation measurements made at kT=24 keV. The cross section of 205Tl(n,gamma) is particularly relevant because it affects the equilibrium that is established in some stellar conditions between the 205Tl -> 205Pb bound-state Beta-decay and the 205Pb -> 205Tl E.C. decay. This effect induces a complex interplay which influences the final s-process abundance of both nuclei. We propose to measure accurately and with high resolution the 205Tl(n,gamma) cross section by using a set of four C6D6 detectors in combination with the pulsed neutron-source of CERN n_TOF.Preprin

Measurement of the neutron capture cross-section of 236U

Proposal: Measurement of the neutron capture cross-section of 236UPreprin

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

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

Charm photoproduction results from NA14'

High statistics samples of reconstructed charmed particles have been obtained by the NA14' experiment. Signals are presented in a variety of decay channels, and are used for the measurement of lifetimes and the study of production mechanisms.Postprint (published version

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.Postprint (published version

Ver, observar, pensar. El proyecto fotográfico personal desde una perspectiva artográfica

Desde una visión de las corrientes contemporáneas de la educación artística el papel del educador es triple: artista, investigador y profesor. La a/r/tografía es la fuente de inspiración del taller Walkscapes en el que un grupo de adolescentes, sin experiencia previa, desarrolla un proyecto fotográfico personal que tendrá un epílogo en una exposición colectiva. Cualquier persona puede sentirse artista si es expuesto a una provocación intelectual adecuada que espolee su creatividad. Los ingredientes que se ponen en juego son la libertad de elección, la reflexión sobre la identidad, la búsqueda o creación de entornos que faciliten la experimentación, la promoción de la duda y el error como motores del proceso, la exposición a referentes diversos, desconocidos y de calidad contrastada, de la fotografía, del cine, la literatura, la música, la filosofía, la ciencia, la ilustración, el diseño... y, sobre todo, la espera

The BRIKEN Project: extensive measurements of ß-delayed neutron emitters for the astrophysical r process

An ambitious program to measure decay properties, primarily ß-delayed neutron emission probabilities and half-lives, for a significant number of nuclei near or on the path of the rapid neutron capture process, has been launched at the RIKEN Nishina Center. We give here an overview of the status of the project.Postprint (published version

Measurement of the 235U(n,f) cross section relative to the 6Li(n,t) and 10B(n,a) standards from thermal to 170 keV neutron energy range at n_TOF

The 235U(n,f) cross section was measured in a wide energy range at n_TOF relative to 6Li(n,t) and 10B(n,alpha), with high resolution and in a wide energy range, with a setup based on a stack of six samples and six silicon detectors placed in the neutron beam. This allowed us to make a direct comparison of the reaction yields under the same experimental conditions, and taking into account the forward/backward emission asymmetry. A hint of an anomaly in the 10÷30 keV neutron energy range had been previously observed in other experiments, indicating a cross section systematically lower by several percent relative to major evaluations. The present results indicate that the evaluated cross section in the 9÷18 keV neutron energy range is indeed overestimated, both in the recent updates of ENDF/B-VIII.0 and of the IAEA reference data. Furthermore, these new high-resolution data confirm the existence of resonance-like structures in the keV neutron energy region. The new, high accuracy results here reported may lead to a reduction of the uncertainty in the 1÷100 keV neutron energy region. Finally, the present data provide additional confidence on the recently re-evaluated cross section integral between 7.8 and 11 eV.Preprin