The impulse approximation for capture of atomic K-shell electrons by incident protons is investigated with respect to a realistic treatment of the initial and intermediate states of the atomic target. Explicit evaluations are made in the single-electron picture described by an effective target potential of Yukawa type. When compared with corresponding results within the standard hydrogenic description, it is found that the effect of proper screening is similar to the effect of off-shell factors found in the strong-potential Born approximation. Effort should therefore be directed towards a study of the combined effect in order to obtain a more complete understanding of the electron capture process.
We have investigated the microstructures of large-grain RE123 (RE = Y, Sm) bulk superconductors with an emphasis placed on the effects of subgrains on superconducting properties. For the samples grown by slow-cooling, the misorientation angles of the subgrains were larger at the later stage of the growth. For isothermally grown samples, subgrains are likely to form under large undercooling. Based on the results of micro-area x-ray pole figure analyses, the possible mechanism of subgrain formation was concluded to be the accumulation of dislocations formed as a result of entrapment of RE211 inclusions during crystal growth. Both magnetization and transport measurements showed that the subgrains act as weak-links.Hence the amount of subgrains should be minimized for the fabrication of high performance large-grain RE123 materials.
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