75 research outputs found

    Thermal neutron capture cross section of the radioactive isotope Fe 60

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    Background: Fifty percent of the heavy element abundances are produced via slow neutron capture reactions in different stellar scenarios. The underlying nucleosynthesis models need the input of neutron capture cross sections. Purpose: One of the fundamental signatures for active nucleosynthesis in our galaxy is the observation of long-lived radioactive isotopes, such as Fe60 with a half-life of 2.60×106 yr. To reproduce this Îł activity in the universe, the nucleosynthesis of Fe60 has to be understood reliably. Methods: An Fe60 sample produced at the Paul Scherrer Institut (Villigen, Switzerland) was activated with thermal and epithermal neutrons at the research reactor at the Johannes Gutenberg-UniversitĂ€t Mainz (Mainz, Germany). Results: The thermal neutron capture cross section has been measured for the first time to σth=0.226(-0.049+0.044)b. An upper limit of σRI<0.50b could be determined for the resonance integral. Conclusions: An extrapolation towards the astrophysically interesting energy regime between kT=10 and 100 keV illustrates that the s-wave part of the direct capture component can be neglected

    179^{179}Ta(n, Îł) cross-section measurement and the astrophysical origin of the 180^{180}Ta isotope

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    180m^{180m}Ta is nature\u27s rarest (quasi) stable isotope and its astrophysical origin is an open question. A possible production site of this isotope is the slow neutron capture process in asymptotic giant branch stars, where it can be produced via neutron capture reactions on unstable 179^{179}Ta. We report a new measurement of the 179^{179}Ta(n,Îł) 180^{180}Ta cross section at thermal-neutron energies via the activation technique. Our results for the thermal and resonance-integral cross sections are 952±57 and 2013±148 b, respectively. The thermal cross section is in good agreement with the only previous measurement [Phys. Rev. C 60, 025802 (1999)], while the resonance integral is different by a factor of ≈1.7. While neutron energies in this work are smaller than the energies in a stellar environment, our results may lead to improvements in theoretical predictions of the stellar cross section

    The unusual spectral energy distribution of LBQS 0102-2713

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    We have studied the SED of the quasar LBQS 0102-2713. The available multiwavelength data are one optical spectrum between 3200 and 7400 A, 7 HST FOS spectra between 1700 and 2300 A, one GALEX NUV flux density and a K_S magnitude obtained from NED, and 3 public ROSAT PSPC pointed observations in the 0.1−-2.4 keV energy band. The alpha_ox values obtained are -2.3 and -2.2, respectively, comparable to BAL quasars. The ROSAT photon index is 6.0+-1.3. The 2500 A luminosity density is about a factor of 10 higher compared to the mean of the most luminous SDSS quasars. We argue that the object might be indicative for a new class of quasars with an unusual combination in their UV-, X-ray, and N_H properties.Comment: 16 pages, 8 figures, accepted by Ap

    The 33S(n,α)30Si cross section measurement at n-TOF-EAR2 (CERN) : From 0.01 eV to the resonance region

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    The 33S(n,α)30Si cross section measurement, using 10B(n,α) as reference, at the n-TOF Experimental Area 2 (EAR2) facility at CERN is presented. Data from 0.01 eV to 100 keV are provided and, for the first time, the cross section is measured in the range from 0.01 eV to 10 keV. These data may be used for a future evaluation of the cross section because present evaluations exhibit large discrepancies. The 33S(n,α)30Si reaction is of interest in medical physics because of its possible use as a cooperative target to boron in Neutron Capture Therapy (NCT)

    Measurement of 73 Ge(n,Îł) cross sections and implications for stellar nucleosynthesis

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    © 2019 The Author(s). Published by Elsevier B.V.73 Ge(n,γ) cross sections were measured at the neutron time-of-flight facility n_TOF at CERN up to neutron energies of 300 keV, providing for the first time experimental data above 8 keV. Results indicate that the stellar cross section at kT=30 keV is 1.5 to 1.7 times higher than most theoretical predictions. The new cross sections result in a substantial decrease of 73 Ge produced in stars, which would explain the low isotopic abundance of 73 Ge in the solar system.Peer reviewe

    Measurement of the 240Pu(n,f) cross-section at the CERN n-TOF facility : First results from experimental area II (EAR-2)

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    The accurate knowledge of the neutron-induced fission cross-sections of actinides and other isotopes involved in the nuclear fuel cycle is essential for the design of advanced nuclear systems, such as Generation-IV nuclear reactors. Such experimental data can also provide the necessary feedback for the adjustment of nuclear model parameters used in the evaluation process, resulting in the further development of nuclear fission models. In the present work, the 240Pu(n,f) cross-section was measured at CERN's n-TOF facility relative to the well-known 235U(n,f) cross section, over a wide range of neutron energies, from meV to almost MeV, using the time-of-flight technique and a set-up based on Micromegas detectors. This measurement was the first experiment to be performed at n-TOF's new experimental area (EAR-2), which offers a significantly higher neutron flux compared to the already existing experimental area (EAR-1). Preliminary results as well as the experimental procedure, including a description of the facility and the data handling and analysis, are presented

    High-accuracy determination of the neutron flux in the new experimental area n_TOF-EAR2 at CERN

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    A new high flux experimental area has recently become operational at the n_TOF facility at CERN. This new measuring station, n_TOF-EAR2, is placed at the end of a vertical beam line at a distance of approximately 20m from the spallation target. The characterization of the neutron beam, in terms of flux, spatial profile and resolution function, is of crucial importance for the feasibility study and data analysis of all measurements to be performed in the new area. In this paper, the measurement of the neutron flux, performed with different solid-state and gaseous detection systems, and using three neutron-converting reactions considered standard in different energy regions is reported. The results of the various measurements have been combined, yielding an evaluated neutron energy distribution in a wide energy range, from 2meV to 100MeV, with an accuracy ranging from 2%, at low energy, to 6% in the high-energy region. In addition, an absolute normalization of the n_TOF-EAR2 neutron flux has been obtained by means of an activation measurement performed with 197Au foils in the beam.Peer reviewe