Two-subband electron transport in nonideal quantum wells

Electron transport in nonideal quantum wells (QW) with large-scale variations of energy levels is studied when two subbands are occupied. Although the mean fluctuations of these two levels are screened by the in-plane redistribution of electrons, the energies of both levels remain nonuniform over the plane. The effect of random inhomogeneities on the classical transport is studied within the framework of a local response approach for weak disorder. Both short-range and small-angle scattering mechanisms are considered. Magnetotransport characteristics and the modulation of the effective conductivity by transverse voltage are evaluated for different kinds of confinement potentials (hard wall QW, parabolic QW, and stepped QW).Comment: 10 pages, 6 figure

Characterization and determination of the gamma radiation attenuation coefficient in the W20Cu3Ni metallic alloy to be applied in the transport of radioactive substances

The final responsibility of civil society protection regarding the nuclear sector in every country is a local/national governmental duty. The way this task is wielded changes little from country to country. The principal concern is to reduce the exposure of people to sources that eventually emit radiation. The shield used for this purpose is called biological shielding. The W20Cu3Ni metallic alloy was obtained using W powder as a matrix and the infiltrating elements Cu and Ni and subjected to sintering processes at different temperatures. All samples were analyzed by X-ray diffractometry, scanning electron microscopy (SEM). The main objective of this work is to determine the gamma radiation attenuation coefficients of the W20Cu3Ni metallic alloy subjected to different sintering temperatures. The determination of the alloy attenuation coefficient was performed using an experiment set up with a source of cobalt (Co-60), which emits characteristic energy peaks of 1.173 MeV and 1.332 MeV. The gamma rays are focused to reach the detector and the resulting photons are counted for 1800 s in three situations. Initially, the gamma rays are directed to the detector in a free path. The second experiment consists of using pure tungsten to shield the radiation, i.e., all gamma rays have to pass through it before entering the detector. Finally, the metallic alloy replaces tungsten, and the same measurements are done. Despite the amount of copper and nickel present in the final sample, the results obtained for this new metallic alloy are very satisfactory. The measurements of the gamma attenuation coefficient in the W20Cu3Ni metallic alloy at different temperatures, showed significant results, ie, a difference between 7.08% and 14.63% lower than the attenuation coefficient of pure tungsten used as a reference. Therefore, this new W20Cu3Ni metal alloy has excellent potential for application in shielding systems and in the transport of substances with high nuclear activity used in the production of radioisotopes and radiopharmaceuticals