[en] The radioactivity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K natural radionuclides in Lao Portland cement samples were measured using a gamma-spectrometry with a HPGe detector. The activity concentrations were found to vary from 28.32 ± 2.23 to 65.50 ± 2.83 Bq kg-1 with a mean value of 41.12 ± 2.44 Bq kg^-1 for ²²⁶Ra; from 7.25 ± 2.00 to 44.01 ± 2.45 Bq kg^-1 with a mean of 16.60 ± 2.37 Bq kg^-1 for ²³²Th and from 49.19 ± 4.27 to 196.74 ± 4.75 Bq kg^-1 with a mean of 141.48 ± 4.50 Bq kg^-1 for ⁴⁰K, respectively. The radiological parameters were estimated to assess the potential radiological hazard including radium equivalent activity, total external absorbed dose rate in outdoor air at 1 m above the earth's surface, the annual effective dose, the gamma and alpha-indices were calculated using the activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K. The results obtained in this study show no significant radiological hazards arising from using Lao Portland cement for building construction. (authors)

[en] In this paper, we study relativistic Landau levels on a spheroidal fullerene molecule in the presence of a crossed electric and magnetic field. A specific profile of external fields is considered as an illustration to examine the dependence of Landau levels on electric field strength and two geometric parameters, namely the Gaussian curvature and ellipticity of the spheroidal molecule. Similar to results in other allotropes of carbon such as spherical fullerene or carbon pseudosphere, the electric field induces a collapse of the Landau levels while the Gaussian curvature tends to prevent them from collapse. However, the ellipticity does not play any role in preventing the collapse of the Landau levels. Furthermore, in certain limiting cases are results agree with those obtained for flat graphene and carbon nanotubes.

[en] Recent experiments have shown that the electron-hole interaction in monolayer materials, such as MoS₂, MoSe₂, WS₂, WSe₂, is no longer Coulombic but screened by the effect of reduced dimensionality, effectively described by the Keldysh potential. In this paper, we develop an algebraic method for calculating energies of a screened exciton in a two-dimensional space with a constant magnetic field. First, we use the Levi-Civita transformation to rewrite the problem into an anharmonic oscillator which can be solved by the algebraic technique based on annihilation and creation operators. Second, we modify the Feranchuk-Komarov operator method to use on the Schrödinger equation. As a result, we are able to obtain high-accuracy numerical solutions with the precision of twelve decimal places for the ground and highly excited states. In our simulation, such high precision persists even for much stronger magnetic field intensities and much longer Keldysh screening length than the present experimental values. Therefore, our numerical data can sufficiently cover most practical analyses. Furthermore, we compare them with the recent experimental data and analyze the screening effect with a conclusion that it strongly enhances the magnetic field effect. Notably, comparing the experimental 1s − 2s and 2s − 3s energy differences with the theoretical calculations, we can predict the screening length and the exciton reduced mass in the monolayers.