Research Articles (Physics)

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Browsing Research Articles (Physics) by Subject "Astrophysics"

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    Galactic production of 138La : Impact of 138,139La statistical properties
    (Elsevier, 2015) Kheswa, B. V.; Wiedeking, M.; Giacoppo, F.; Goriely, S.; Guttormsen, M.; Larsen, A. C.; Bello Garrote, F. L.; Eriksen, T. K.; Gorgen, A.; Hagen, T. W.; Koehler, P. E.; Klintefjord, M.; Nyhus, H. T.; Papka, P.; Renstrom, T.; Rose, S.; Sahin, E.; Siem, S.; Tornyi, T.
    The γ-ray strength functions and nuclear level densities of 138La and 139La have been measured below the neutron separation energies. These new data were used to calculate astrophysical Maxwellian-averaged (n, γ) cross-sections to investigate the production and destruction of the p-nucleus 138La in the photodisintegration process. The results confirm the underproduction of 138La in the p-process with respect to the observed abundances and strongly support the ν-process through νecapture on 138Ba as the main contributor to the synthesis of 138La in Type II supernovae.
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    Re-estimation of 180Ta nucleosynthesis in light of newly constrained reaction rates
    (Elsevier, 2019-03-12) Malatji, K. L.; Wiedeking, M.; Goriely, S.; Brits, C. P.; Kheswa, B. V.; Bello Garrote, F. L.; Bleuel, D. L.; Giacoppo, F.; Gorgen, A.; Guttormsen, M.; Hadynska-Klek, K.; Hagen, T. W.; Ingeberg, V. W.; Klintefjord, M.; Larsen, A. C.; Papka, P.; Renstrom, T.; Sahin, E.; Siem, S.; Siess, L.; Tveten, G. M.; Zeiser, F.
    Recent measurements of the nuclear level densities and γ-ray strength functions below the neutron thresholds in 180,181,182Ta are used as input in the nuclear reaction code TALYS. These experimental average quantities are utilized in the calculations of the 179,180,181Ta radiative neutron capture cross sections. From the latter, astrophysical Maxwellian-averaged (n, γ) cross sections (MACS) and reaction rates are extracted, which in turn are used in large astrophysical network calculations to probe the production mechanism of 180Ta. These calculations are performed for two scenarios, the s-process production of 180,181Ta in Asymptotic Giant Branch (AGB) stars and the p-process nucleosynthesis of 180Tamin Type-II supernovae. Based on the results from this work, the s-process in stellar evolution is considered negligible in the production of 180Tamwhereas 181Ta is partially produced by AGB stars. The new measurements strongly constrain the production and destruction rates of 180Tamat p-process temperatures and confirm significant production of nature’s rarest stable isotope 180Tamby the p-process.