Browsing by Author "Larsen, A. C."

Now showing 1 - 4 of 4
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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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    ¹³⁷,¹³⁸,¹³⁹La(n,γ) cross sections constrained with statistical decay properties of ¹³⁸,¹³⁹,¹⁴⁰La nuclei
    (American Physical Society, 2017) Kheswa, B. V.; Wiedeking, M.; Brown, J. A.; Larsen, A. C.; Goriely, S.; Guttormsen, M.; Garrote, F. L. Bello; Bernstein, L. A.; Bleuel, D. L.; Eriksen, T. K.; Giacoppo, F.; Gorgen, A.; Goldblum, B. L.; Hagen, T. W.; Koehler, P. E.; Klintefjord, M.; Malatji, K. L.; Midtbo, J. E.; Nyhus, H. T.; Papka, P.; Renstrm, T.; Rose, S. J.; Sahin, E.; Siem, S.; Tornyi, T. G.
    The nuclear level densities and γ-ray strength functions of ¹³⁸,¹³⁹,¹⁴⁰La were measured using the ¹³⁹La(³He,α), ¹³⁹La(³He,'³He), and ¹³⁹La(d,p) reactions. The particle-γ coincidences were recorded with the silicon particle telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these experimental results, the low-energy enhancement in the A∼140 region is discussed. The ¹³⁷,¹³⁸,¹³⁹La(n,γ) cross sections were calculated at s- and p-process temperatures using the experimentally measured nuclear level densities and γ-ray strength functions. Good agreement is found between ¹³⁹La(n,γ) calculated cross sections and previous measurements.
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    Nuclear level densities and γ-ray strength functions of 180,181,182Ta
    (American Physical Society, 2019) Brits, C. P.; Malatji, K. L.; Wiedeking, M.; Kheswa, B. V.; Goriely, S.; Garrote, F. L. Bello; Bleuel, D. L.; Giacoppo, F.; Gorgen, A.; Guttormsen, M.; Hadynska-Klek, K.; Hagen, T. W.; Hilaire, S.; Ingeberg, V. W.; Klintefjord, H. Jia M.; Larsen, A. C.; Majola, S. N. T.; Papka, P.; Peru, S.; Qi, B.; Renstrom, T.; Rose, S. J.; Sahin, E.; Siem, S.; Tveten, G. M.; Zeiser, F.
    Particle-γ coincidence experiments were performed at the Oslo Cyclotron Laboratory with the ¹⁸¹Ta(d,X) and ¹⁸¹Ta(³He,X) reactions to measure the nuclear level densities (NLDs) and γ-ray strength functions (γSFs) of ¹⁸⁰,¹⁸¹,¹⁸²Ta using the Oslo method. The back-shifted Fermi-gas, constant temperature plus Fermi gas, and Hartree-Fock-Bogoliubov plus combinatorial models were used for the absolute normalizations of the experimental NLDs at the neutron separation energies. The NLDs and γSFs are used to calculate the corresponding ¹⁸¹Ta(n,γ) cross sections and these are compared to results from other techniques. The energy region of the scissors resonance strength is investigated and from the data and comparison to prior work it is concluded that the scissors strength splits into two distinct parts. This splitting may allow for the determination of triaxiality and a γ deformation of 14.9˚±1.8˚ was determined for ¹⁸¹Ta.
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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.