The theoretical analysis of the reaction taking place in both metallic as well as gaseous targets at deuteron energies of several keV presented here indicates a strong contribution of the single-particle threshold resonance. Additional arguments based on the weak coupling between the 2 + 2 and 3 + 1 clustering states of the compound nucleus support this resonance and suggest its large partial width for the internal electron-positron pair formation that overestimates the proton width. A detailed study of the interplay between the resonance transition and the electron screening effect enables estimation of the nuclear reaction rate of the deuteron-deuteron fusion reactions at room temperature.
17 January 2019 in Radiation and Environmental Biophysics
We investigated induction of chromosome aberrations (CA) in human lymphocytes when exposed to 150 MeV and spread out Bragg peak (SOBP) proton beams, and 199 MeV/u carbon beam which are currently widely used for cancer treatment and simultaneously are important components of cosmic radiation. For a comparison, the boron ions of much lower energy 22 MeV/u and a 60Co γ rays were used. Dose–effect curves as well as the distributions of CA were studied using Poisson and Neyman type A statistics. Systematics of experimentally determined parameters, their dependence on applied doses and irradiation quality are presented.
The angular distribution of the reaction at deuteron energies below and the total cross section as well as the angular distribution of the reaction at energies below have been measured. Based on our experimental results and data of other authors, the reaction mechanism has been studied in a wide energy range, relevant for astrophysical applications. It has been found that in both cases broad resonances in the compound nuclei play the key role for the description of the excitation functions. The long-standing problems of describing the angular distributions could be solved for both reactions by assuming a coherent superposition between resonant and direct reaction amplitudes. A theoretical approach allowing for coherent calculations has been developed. Some astrophysical implications are discussed.
Electron emission in the deuteron-deuteron reaction supporting existence of the single-particle threshold resonance in has been observed for the first time. The measured electron energy spectrum and the electron-proton branching ratio agree very well with the assumed electron-positron pair creation decay of the resonance state to the ground state and the detailed Monte Carlo simulations of the experimental energy spectrum.
A sustainable separation concept for large-scale recycling of NdFeB magnets under atmospheric pressure was developed by utilizing a combination of two separation concepts known from the literature: (I) selective pre-separation by in situ chlorination and evaporation of ground oxidized NdFeB material and (II) subsequent distillation for high-purity recovery of all recyclable chlorinated material components, especially its Rare Earth Elements (REEs). Theoretically, simplified estimations of the time conversion curves at 1173 K, 1273 K, and 2000 K of a single particle resulted in the idea of realizing chlorination in some kind of combustion chamber, fluidized bed, or continuous combustion chamber. After chlorination, all non-volatile components, such as REE chlorides, are condensed out of the vapor phase in a single-stage phase separator. For subsequent fine separation by distillation (1292–1982 K for Rare Earth Chlorides and 418–867 K at 2500 kPa for boron and zirconium chloride recovery), simplified simulations were performed in a total-reflux column under ideal phase equilibrium conditions to show the estimated minimum separation effort. Using two composition examples from the literature, high-purity separation of the major Rare Earth Chlorides within a twelve-stage distillation column as a residual heavy boiling product has been demonstrated to be potentially technically feasible.
Silicon carbide has been considered a material for use in the construction of advanced high-temperature nuclear reactors. However, one of the most important design issues for future reactors is the development of structural defects in SiC under a strong irradiation field at high temperatures. To understand how high temperatures affect radiation damage, SiC single crystals were irradiated at room temperature and after being heated to 800 °C with carbon and silicon ions of energies ranging between 0.5 and 21 MeV. The number of displaced atoms and the disorder parameters have been estimated by using the channeling Rutherford backscattering spectrometry. The experimentally determined depth profiles of induced defects at room temperature agree very well with theoretical calculations assuming its proportionality to the electronic and nuclear-stopping power values. On the other hand, a significant reduction in the number of crystal defects was observed for irradiations performed at high temperatures or for samples annealed after irradiation. Additionally, indications of saturation of the crystal defect concentration were observed for higher fluences and the irradiation of previously defected samples.