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Measurement of the thulium stellar cross section at kT=30 keV by activation with an innovative method

AutorPraena, Javier ; Pignatari, M.; Mastinu, Pierfrancesco; Quesada, José Manuel; Capote-Noy, Roberto
Fecha de publicación2013
ResumenThe production of Maxwell-Boltzmann neutron spectra is of interest in several fields. Maxwellian-averaged cross sections (MACS) ranging from kT=5 keV to 120 keV are key parameters in the calculation of the astrophysical reaction rates of nucleon, photon and charged-particle interactions with the different elements and their isotopes needed among other things for the description of observed elemental abundances. Spectrum average (SPA) cross sections measured in the well-characterized maxwellian neutron spectrum with high accuracy could be used for the validation of nuclear data libraries in the above-mentioned energy range. Both the library cross-section value and corresponding covariances could be challenged. The estimated uncertainty from the nuclear data library of SPA cross sections is directly linked to off-diagonal elements of the uncertainty matrix; therefore the uncertainty of the calculated SPA cross-section is sensitive to librarian covariances. The energy range ~100-200 keV is also extremely important in the description of fast neutron systems (e.g. for fast Generation-IV reactors). The MACS of the different elements can be measured directly by activation providing a maxwellian neutron spectrum at the sample position. Beer and Käppeler is considered the classical work in this field, they showed the possibility to produce a quasi maxwellian neutron spectra at kT=25 keV by the Li-7(p,n) reaction at proton energy near-threshold. Then the MACS at the reference temperature (30 keV) can be obtained by a correction of the spectrum and an extrapolation from 25 to 30 keV. Mastinu et al proposed a new method for producing maxwellian neutron spectra at different temperatures, in particular a very accurate maxwellian spectrum at kT=30 keV can be achieved. While the classical method uses monochromatic proton energy, the key point of the Mastinu et al method is to shape the proton beam to a particular distribution near-threshold the Li-7(p,n) reaction by means of an energy degrader that can be made of different material and thicknesses. The Mastinu et al method is used to measure by activation the MACS of the Tm169(n,g) reaction at kT=30 keV using Au-197(n,g) as a reference. The available experimental data for this reaction is rather limited and there is only one available data for the MACS at kT=30 keV obtained by the TOF technique. The method will be explained and the results will be shown. Around 13% of the solar abundance of Thulium is made by the slow neutron capture process. Astrophysical implications will be discussed for nucleosynthesis in stars driven by s-process.
DescripciónResumen del trabajo presentado a la: "International Conference on Nuclear Data for Science and Technology" celebrada en New York (US) del 4 al 8 de marzo de 2013.-- et al.
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