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At least 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Preparation and characterization of V/TiO{sub 2} nanocatalyst with magnetic nucleus of iron

Graphical abstract: - Highlights: • Fe-V/TiO{sub 2} nanocatalyst is prepared. • Combination of sol–gel and wetness impregnation methods. • Facile separation of catalyst from medium by magnet. - Abstract: A magnetic composite containing V/TiO{sub 2} was prepared by combination of sol–gel and wetness impregnation methods. The effects of synthesis temperature, different weight percents of Fe supported on TiO{sub 2}, vanadium loading and the heating rate of calcination on the structure and morphology of nanocatalyst were investigated. The optimum conditions for synthesized catalyst were 40 wt.% of Fe, 15 wt.% of V and synthesis temperature equal to 30 °C. Characterization of catalyst is carried out using XRD, TGA, DSC, SEM, FTIR and N{sub 2} physisorption measurements. The magnetic character of nanocatalyst was measured using VSM, which showed the typical paramagnetic behavior of sample at room temperature with a saturation magnetization value equal to 8.283 emu/g. The nanocatalyst has a particle size about 56 nm and can easily be separated from medium by a magnet.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Quantifying uncertainties in α -nucleus reaction dynamics informed from first principles

The ab initio symmetry-adapted no-core shell model is a microscopic many-body method which naturally describes challenging collective and clustering features of atomic nuclei. Wave functions and observables computed with realistic nucleon-nucleon forces in this framework are tied to first principles, and are hence well-suited for rigorous uncertainty quantification. We discuss α-deuteron and α- 12 C cluster potentials informed by symmetry-adapted calculations, and propagate uncertainties in the effective binary cluster method as well as those in the nuclear interaction to reaction observables, namely scattering phase shifts, cross sections, partial widths and resonance energies. Here, we find that the overall uncertainties are dominated by those originating in the underlying nuclear force, speaking to the need for tighter constraints on realistic nucleon-nucleon interactions.

Ab initio↗
DOE OSTI2019

Most theoretical approaches used in nuclear astrophysics to model the nucleosynthesis of heavy elements incorporate the so-called statistical model in order to describe the excitation and decay properties of atomic nuclei. One of the basic assumptions of this model is the validity of the Brink–Axel hypothesis and the related concept of so-called photon strength functions to describe γ-ray transition probabilities. We present a novel experimental approach that allows for the first time to experimentally determine the photon strength function simultaneously in two independent ways by a unique combination of quasi-monochromatic photon beams and a newly implemented γ–γ coincidence setup. This technique does not assume a priori the validity of the Brink–Axel hypothesis and sets a benchmark in terms of the detection sensitivity for measuring decay properties of photo-excited states below the neutron separation energy. The data for the spherical off-shell nucleus 128 Te were obtained for γ-ray beam-energy settings between 3 MeV and 9 MeV in steps of 130 keV for the lower beam energies and in steps of up to 280 keV for the highest beam settings. We present a quantitative analysis on the consistency of the derived photon strength function with the Brink–Axel hypothesis. The data clearly demonstrate a discrepancy of up to a factor of two between the photon strength functions extracted from the photoabsorption and photon emission process, respectively. In addition, we observe that the photon strength functions are not independent of the excitation energy, as usually assumed. Thus, we conclude, that the Brink–Axel hypothesis is not strictly fulfilled in the excitation-energy region below the neutron separation threshold (S n = 8.78 MeV) for the studied case of 128 Te.

Not Available

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗