409 research outputs found

    The neutron time-of-flight facility n TOF at CERN. Recent facility upgrades and detector developments

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    Part of this work has been carried out in the framework of a project funded by the European Research Council (ERC) under the European Union‚Äôs Horizon 2020 research and innovation programme (ERC Consolidator Grant project HYMNS, with grant agreement No. 681740). The authors acknowledge support from the Spanish Ministerio de Ciencia e Innovaci¬īon under grants PID2019-104714GB-C21, FPA2017-83946-C2-1-P and FIS2015-71688-ERC. In line with the principles that apply to scientific publishing and the CERN policy in matters of scientific publications, the n TOF Collaboration recognises the work of V. Furman and Y. Kopatch (JINR, Russia), who have contributed to the experiment used to obtain the results described in this paper.Based on an idea by Carlo Rubbia, the n_TOF facility at CERN has been operating for over 20 years. It is a neutron spallation source, driven by the 20 GeV/c proton beam from the CERN PS accelerator. Neutrons in a very wide energy range (from GeV, down to sub-eV kinetic energy) are generated by a massive Lead spallation target feeding two experimental areas. EAR1, horizonal with respect to the proton beam direction is set at 185 meters from the spallation target. EAR2, on the vertical line from the spallation source, is placed at 20 m. Neutron energies for experiments are selected by the time-of-flight technique (hence the name n_TOF), while the long flight paths ensure a very good energy resolution. Over one hundred experiments have been performed by the n_TOF Collaboration at CERN, with applications ranging from nuclear astrophysics (synthesis of the heavy elements in stars, big bang nucleosynthesis, nuclear cosmo-chronology), to advanced nuclear technologies (nuclear data for applications, nuclear safety), as well as for basic nuclear science (reaction mechanisms, structure and decay of highly excited compound states). During the planned shutdown of the CERN accelerator complex between 2019 and 2021, the facility went through a substantial upgrade with a new target-moderator assembly, refurbishing of the neutron beam lines and experimental areas. An additional measuring and irradiation station (the NEAR Station) has been envisaged and its capabilities for performing material test studies and new physics opportunities are presently explored. An overview of the facility and of the activities performed at CERN is presented in this contribution, with a particular emphasis on the most relevant experiments for nuclear astrophysics.European Research Council (ERC) under the European Union‚Äôs Horizon 2020 research and innovation programme (ERC Consolidator Grant project HYMNS, with grant agreement No. 681740)Spanish Ministerio de Ciencia e Innovaci√≥n under grants PID2019-104714GB-C21, FPA2017-83946-C2-1-P and FIS2015-71688-ERC

    Desarrollo de un método de transcripción inversa seguida de reacción en cadena de la polimerasa para la detección del virus de la fiebre amarilla

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    Introduction. Yellow fever is considered a re-emerging disease and is endemic in tropical regions of Africa and South America. At present, there are no standardized or commercialized kits available for yellow fever virus detection. Therefore, diagnosis must be made by time-consuming routine techniques, and sometimes, the virus or its proteins are not detected. Furthermore, co-circulation with other flaviviruses, including dengue virus, increases the difficulty of diagnosis.Objective. To develop a specific reverse transcriptase-polymerase chain reaction (RT-PCR) and nested PCR-based assay to improve the detection and diagnosis of yellow fever virus using both serum and fresh tissue samples.Materials and methods. RT-PCR primers were designed to amplify a short fragment of all yellow fever virus genotypes reported. A second set of primers was used in a nested PCR to increase sensitivity. Thirty-three clinical samples were tested with the standardized reaction.Results. The expected amplicon was obtained in 25 out of 33 samples analyzed using this approach, and 2 more samples tested positive after a subsequent nested PCR approach.Conclusion. This improved technique not only ensures the specific detection of a wide range of yellow fever virus genotypes but also may increase the sensitivity of detection by introducing a second round of amplification, allowing a rapid differential diagnosis between dengue and yellow fever infection, which is required for effective surveillance and opportune epidemiologic measures.¬†doi: http://dx.doi.org/10.7705/biomedica.v33i0.1452Introducci√≥n. La fiebre amarilla se considera una enfermedad reemergente y end√©mica en regiones tropicales de √Āfrica y Suram√©rica. Actualmente, no existen estuches estandarizados o comerciales disponibles para la detecci√≥n del virus de la fiebre amarilla y, por lo tanto, el diagn√≥stico debe hacerse mediante t√©cnicas de rutina que consumen mucho tiempo y algunas veces no garantizan la detecci√≥n del virus o de sus prote√≠nas. Adem√°s, la cocirculaci√≥n con otros flavivirus, incluyendo el del dengue, hacen el diagn√≥stico m√°s complicado.Objetivo. Desarrollar un ensayo espec√≠fico de amplificaci√≥n basado en transcripci√≥n inversa seguida de reacci√≥n en cadena de la polimerasa, con el fin de mejorar la detecci√≥n y el diagn√≥stico de la fiebre amarilla, tanto a partir de suero como de tejido fresco.Materiales y m√©todos. Se dise√Īaron iniciadores espec√≠ficos para amplificar un fragmento conservado del virus de la fiebre amarilla. Un segundo par de iniciadores se us√≥ en una reacci√≥n de amplificaci√≥n anidada para incrementar la sensibilidad. Se probaron 33 muestras cl√≠nicas con la t√©cnica estandarizada.Resultados. El ampl√≠mero esperado se obtuvo en 25 de las 33 muestras analizadas usando este m√©todo y 2 m√°s resultaron positivas despu√©s de la reacci√≥n anidada.Conclusi√≥n. Esta t√©cnica mejorada garantiza la detecci√≥n de todos los genotipos virales de fiebre amarilla y puede incrementar la sensibilidad del ensayo introduciendo una segunda etapa de amplificaci√≥n, lo cual permite el diagn√≥stico diferencial con infecci√≥n por dengue y otros flavivirus, lo cual es de gran importancia para la vigilancia y la toma de medidas epidemiol√≥gicas oportunas.doi: http://dx.doi.org/10.7705/biomedica.v33i0.1452

    Determination of the stellar (n,gamma) cross section of 40Ca with accelerator mass spectrometry

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    The stellar (n,gamma) cross section of 40Ca at kT=25 keV has been measured with a combination of the activation technique and accelerator mass spectrometry (AMS). This combination is required when direct off-line counting of the produced activity is compromised by the long half-life and/or missing gamma-ray transitions. The neutron activations were performed at the Karlsruhe Van de Graaff accelerator using the quasistellar neutron spectrum of kT=25 keV produced by the 7Li(p,n)7Be reaction. The subsequent AMS measurements were carried out at the Vienna Environmental Research Accelerator (VERA) with a 3 MV tandem accelerator. The doubly magic 40Ca is a bottle-neck isotope in incomplete silicon burning, and its neutron capture cross section determines the amount of leakage, thus impacting on the eventual production of iron group elements. Because of its high abundance, 40Ca can also play a secondary role as "neutron poison" for the s-process. Previous determinations of this value at stellar energies were based on time-of-flight measurements. Our method uses an independent approach, and yields for the Maxwellian-averaged cross section at kT=30 keV a value of 30 keV= 5.73+/-0.34 mb.Comment: 8 pages, 3 figure

    Measurement of the radiative neutron capture cross section of 206 Pb and its astrophysical implications

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    The (n,ő≥) cross section of 206Pb has been measured at the CERN n_TOF facility with high resolution in the energy range from 1 eV to 620 keV by using two optimized 6C6D detectors. In the investigated energy interval about 130 resonances could be observed, from which 61 had enough statistics to be reliably analyzed via the R-matrix analysis code SAMMY. Experimental uncertainties were minimized, in particular with respect to (i) angular distribution effects of the prompt capture ő≥-rays, and to (ii) the TOF-dependent background due to sample-scattered neutrons. Other background components were addressed by background measurements with an enriched 208Pb sample. The effect of the lower energy cutoff in the pulse height spectra of the 6C6D detectors was carefully corrected via Monte Carlo simulations. Compared to previous 206Pb values, the Maxwellian averaged capture cross sections derived from these data are about 20% and 9% lower at thermal energies of 5 keV and 30 keV, respectively. These new results have a direct impact on the s-process abundance of 206Pb, which represents an important test for the interpretation of the cosmic clock based on the decay of 238U

    First tests of the applicability of gamma-ray imaging for background discrimination in time-of-flight neutron capture measurements

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    In this work we explore for the first time the applicability of using gamma-ray imaging in neutron capture measurements to identify and suppress spatially localized background. For this aim, a pinhole gamma camera is assembled, tested and characterized in terms of energy and spatial performance. It consists of a monolithic CeBr3 scintillating crystal coupled to a position-sensitive photomultiplier and readout through an integrated circuit AMIC2GR. The pinhole collimator is a massive carven block of lead. A series of dedicated measurements with calibrated sources and with a neutron beam incident on a Au-197 sample have been carried out at n_TOF, achieving an enhancement of a factor of two in the signal-to-background ratio when selecting only those events coming from the direction of the sample. (C) 2016 Elsevier B.V. All rights reserved.Postprint (author's final draft

    Neutron Capture on the s-Process Branching Point Tm 171 via Time-of-Flight and Activation

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    The neutron capture cross sections of several unstable nuclides acting as branching points in the s process are crucial for stellar nucleosynthesis studies. The unstable 171Tm (t1/2=1.92yr) is part of the branching around mass A‚ąľ170 but its neutron capture cross section as a function of the neutron energy is not known to date. In this work, following the production for the first time of more than 5 mg of 171Tm at the high-flux reactor Institut Laue-Langevin in France, a sample was produced at the Paul Scherrer Institute in Switzerland. Two complementary experiments were carried out at the neutron time-of-flight facility (n_TOF) at CERN in Switzerland and at the SARAF liquid lithium target facility at Soreq Nuclear Research Center in Israel by time of flight and activation, respectively. The result of the time-of-flight experiment consists of the first ever set of resonance parameters and the corresponding average resonance parameters, allowing us to make an estimation of the Maxwellian-averaged cross sections (MACS) by extrapolation. The activation measurement provides a direct and more precise measurement of the MACS at 30 keV: 384(40) mb, with which the estimation from the n_TOF data agree at the limit of 1 standard deviation. This value is 2.6 times lower than the JEFF-3.3 and ENDF/B-VIII evaluations, 25% lower than that of the Bao et al. compilation, and 1.6 times larger than the value recommended in the KADoNiS (v1) database, based on the only previous experiment. Our result affects the nucleosynthesis at the A‚ąľ170 branching, namely, the 171Yb abundance increases in the material lost by asymptotic giant branch stars, providing a better match to the available pre-solar SiC grain measurements compared to the calculations based on the current JEFF-3.3 model-based evaluation.The authors acknowledge financial support by University of Seville via the V PPIT-US programme, the Spanish Ministerio de Econom√≠a y Competitividad FPA2013-45083-P, FPA2014-53290-C2-2-P and FPA2016-77689-C2-1-R projects, the EC FP7 projects NeutAndalus (Grant No. 334315) and CHANDA (Grant No. 605203), and the n_TOF Collaboration. The SARAF-LiLiT experiment was supported by the Pazy Foundation (Israel). M.‚ÄČP. acknowledges support of the Israel Science Foundation (Grant No. 1387/15). The University of Edinburgh acknowledges funding from the Science and Technology Facilities Council UK (ST/M006085/1), and the European Research Council ERC-2015-STG No. 677497
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