710 research outputs found

    Neutron cross sections in stellar nucleosynthesis: Study of the key isotope 25Mg

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    In this document the important role of 25Mg within nucleosynthesis processes is studied. In fact the initial conditions of s-process in massive and AGB stars depend on neutron-induced reactions on 25Mg, being this isotope involved both in neutron production and as a neutron poison. Because of the importance of 25Mg, very accurate and precise measurements of its capture cross section, at the n TOF CERN facility, and of its total cross section, at the EC-JRC-IRMM facility in Belgium, were performed. The aims of these measurements are both to weight the contribution of 25Mg as a neutron poison and to give constraints for the reaction rate of one of the main neutron sources for the s-process

    Status and perspectives of the neutron time-of-flight facility n_TOF at CERN

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    The neutron time-of-flight facility of CERN, called n TOF, started its operation in 2001, and since then it plays a major role in the field of neutron cross-section measurements. The two beam-lines available provide an excellent combination of good energy resolution and high instantaneous neutron flux, combining the time-of-flight method with a powerful neutron spallation source. So far, a large number of experiments has been performed on a variety of isotopes of interest for nuclear astrophysics, advanced nuclear technologies, nuclear medicine, and for basic nuclear physics. After the CERN long shutdown, a new phase of data taking is planned to start in 2021. The R&D of a new spallation target is ongoing and its upgrade will bring important improvements in both beam lines, allowing the n TOF Collaboration to perform new, challenging measurements

    Duodenal-Jejunal Bypass and Jejunectomy Improve Insulin Sensitivity in Goto-Kakizaki Diabetic Rats Without Changes in Incretins or Insulin Secretion

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    Gastric bypass surgery can dramatically improve type 2 diabetes. It has been hypothesized that by excluding duodenum and jejunum from nutrient transit, this procedure may reduce putative signals from the proximal intestine that negatively influence insulin sensitivity ( S I ). To test this hypothesis, resection or bypass of different intestinal segments were performed in diabetic Goto-Kakizaki and Wistar rats. Rats were randomly assigned to five groups: duodenal-jejunal bypass (DJB), jejunal resection (jejunectomy), ileal resection (ileectomy), pair-fed sham-operated, and nonoperated controls. Oral glucose tolerance test was performed within 2 weeks after surgery. Baseline and poststimulation levels of glucose, insulin, glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) were measured. Minimal model analysis was used to assess S I . S I improved after DJB ( S I = 1.14 ± 0.32 × 10 −4 min −1 ⋅ pM −1 ) and jejunectomy ( S I = 0.80 ± 0.14 × 10 −4 min −1 ⋅ pM −1 ), but not after ileectomy or sham operation/pair feeding in diabetic rats. Both DJB and jejunal resection normalized S I in diabetic rats as shown by S I levels equivalent to those of Wistar rats ( S I = 1.01 ± 0.06 × 10 −4 min −1 ⋅ pM −1 ; P = NS). Glucose effectiveness did not change after operations in any group. While ileectomy increased plasma GIP levels, no changes in GIP or GLP-1 were observed after DJB and jejunectomy. These findings support the hypothesis that anatomic alterations of the proximal small bowel may reduce factors associated with negative influence on S I , therefore contributing to the control of diabetes after gastric bypass surgery

    Pulse processing routines for neutron time-of-flight data

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    A pulse shape analysis framework is described, which was developed for n_TOF-Phase3, the third phase in the operation of the n_TOF facility at CERN. The most notable feature of this new framework is the adoption of generic pulse shape analysis routines, characterized by a minimal number of explicit assumptions about the nature of pulses. The aim of these routines is to be applicable to a wide variety of detectors, thus facilitating the introduction of the new detectors or types of detectors into the analysis framework. The operational details of the routines are suited to the specific requirements of particular detectors by adjusting the set of external input parameters. Pulse recognition, baseline calculation and the pulse shape fitting procedure are described. Special emphasis is put on their computational efficiency, since the most basic implementations of these conceptually simple methods are often computationally inefficient.Comment: 13 pages, 10 figures, 5 table

    Measurement of the 70Ge(n,γ) cross section up to 300 keV at the CERN n_TOF facility

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    Neutron capture data on intermediate mass nuclei are of key importance to nucleosynthesis in the weak component of the slow neutron capture processes, which occurs in massive stars. The (n,γ) cross section on 70Ge, which is mainly produced in the s process, was measured at the neutron time-of-flight facility n_TOF at CERN. Resonance capture kernels were determined up to 40 keV neutron energy and average cross sections up to 300 keV. Stellar cross sections were calculated from kT =5 keV tokT =100 keV and are in very good agreement with a previous measurement by Walter and Beer (1985) and recent evaluations. Average cross sectionsareinagreementwithWalterandBeer(1985)overmostoftheneutronenergyrangecovered,whilethey aresystematicallysmallerforneutronenergiesabove150keV.Wehavecalculatedisotopicabundancesproduced in s-process environments in a 25 solar mass star for two initial metallicities (below solar and close to solar). While the low metallicity model reproduces best the solar system germanium isotopic abundances, the close to solar model shows a good global match to solar system abundances in the range of mass numbers A=60–80.Austrian Science Fund J3503Adolf Messer Foundation ST/M006085/1European Research Council ERC2015-StGCroatian Science Foundation IP-2018-01-857

    238U(n, γ) reaction cross section measurement with C6D6 detectors at the n_TOF CERN facility

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    INPC 2013 – International Nuclear Physics ConferenceThe 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,γ) cross section measurement performed at n_TOF with C6D6 scintillation detectors are presented, paying particular attention to data reduction and background subtractio

    The nucleosynthesis of heavy elements in stars: the key isotope 25Mg

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    INPC 2013 – International Nuclear Physics ConferenceWe 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 proces

    High precision measurement of the radiative capture cross section of 238U at the n-TOF CERN facility

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    The importance of improving the accuracy on the capture cross-section of 238U has been addressed by the Nuclear Energy Agency, since its uncertainty significantly affects the uncertainties of key design parameters for both fast and thermal nuclear reactors. Within the 7th framework programme ANDES of the European Commission three different measurements have been carried out with the aim of providing the 238U(n,γ) cross-section with an accuracy which varies from 1 to 5%, depending on the energy range. Hereby the final results of the measurement performed at the n TOF CERN facility in a wide energy range from 1 eV to 700 keV will be presented

    The CERN n_TOF facility: a unique tool for nuclear data measurement

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    The study of the resonant structures in neutron-nucleus cross-sections, and therefore of the compoundnucleus reaction mechanism, requires spectroscopic measurements to determine with high accuracy the energy of the neutron interacting with the material under study. To this purpose, the neutron time-of-flight facility n_TOF has been operating since 2001 at CERN. Its characteristics, such as the high intensity instantaneous neutron flux, the wide energy range from thermal to few GeV, and the very good energy resolution, are perfectly suited to perform highquality measurements of neutron-induced reaction cross sections. The precise and accurate knowledge of these cross sections plays a fundamental role in nuclear technologies, nuclear astrophysics and nuclear physics. Two different measuring stations are available at the n_TOF facility, called EAR1 and EAR2, with different characteristics of intensity of the neutron flux and energy resolution. These experimental areas, combined with advanced detection systems lead to a great flexibility in performing challenging measurement of high precision and accuracy, and allow the investigation isotopes with very low cross sections, or available only in small quantities, or with very high specific activity. The characteristics and performances of the two experimental areas of the n_TOF facility will be presented, together with the most important measurements performed to date and their physics case. In addition, the significant upcoming measurements will be introduced.Postprint (published version
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