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Neutron Studies for Dating the Universe
F. Kappeler,A. Mengoni,M. Mosconi,K. Fujii,M. Heil,C. Domingo-pardo,The n_TOF Collaboration 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
The neutron capture cross sections of ^(186)Os and ^(187)Os are of key importance for defining the s-process abundance of ^(187)Os at the formation of the solar system. This quantity can be used to determine the radiogenic abundance component of ^(187)Os from the decay of ^(187)Re (t_(1/2) = 41.2 Gyr) and to infer the time-duration of the nucleosynthesis in our galaxy (Re/Os cosmochronometer). The neutron capture cross sections of ^(186)Os, ^(187)Os, and ^(188)Os have been measured at the CERN n_TOF facility from 1 eV to 1 MeV, covering the entire energy range of astrophysical interest. From these data Maxwellian averaged capture cross sections have been calculated with uncertainties between 3.3 and 4.7%. Additional information was obtained by measuring the inelastic scattering cross section of ^(187)Os at the Karlsruhe 3.7 MV Van de Graaff accelerator and by neutron resonance analyses of the n TOF capture data to establish a comprehensive experimental basis for the Hauser-Feshbach statistical model. Consistent HF calculations for the capture and inelastic reaction channels were performed to determine the stellar enhancement factors, which are required to correct the Maxwellian averaged cross sections for the effect of thermally populated excited states. The consequences of this analysis for the s-process component of the ^(187)Os abundance and the related impact on the evaluation of the time-duration of Galactic nucleosynthesis via the Re/Os cosmo-chronometer are discussed.
Multifragmentation in Reactions of 1-GeV Protons with Iron Nuclei
D. Mancusi,J. Cugnon,A. Boudard,,J. C. David,S. Leray,R. J. Charity,A. Kelic-heil,M. V. Ricciardi 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
We use combinations of cascade and nuclear de-excitation models to assess the importance of the inclusion of a multifragmentation stage for the quantitative description of the 1-GeV p+^(56)Fe spallation reaction. We discuss the sensitivity of several exclusive physical observables to the de-excitation mechanism in the attempt to identify which of them can be considered suitable probes for a multifragmentation stage. The calculations show that the inclusion of a multifragmentation stage is not necessary to construct an accurate description of the observed data.