Vol 45, No 8 (2018)

The formation energy and the Stone—Wales defect structure in fullerene C₂₀ doped with one of functional groups H, Cl, F, or OH are calculated within the density functional theory. It is shown that the functional group type and binding site have a significant effect on the defect formation energy. It is found that the C₂₀F compound is significantly more stable than other considered systems, i.e., C₂₀Cl, C₂₀H, and C₂₀OH.

The low-frequency asymptotic behavior of the spectral distribution density of equilibrium radiation in collisionless non-degenerate electron plasma is studied. It is shown that the consideration of the spatial dispersion in the electron gas permittivity leads to a logarithmic singularity in the spectral distribution density at low frequencies. In this case, the total radiation energy remains finite. The results of the analytical consideration are identical to numerical calculations.

The energy spectrum and the distribution of the total charge over the ion energy are studied for plasma produced by partially coherent radiation of the neodymium glass laser with a power density of ~10¹³ W/cm² in the focusing spot incident on continuous gadolinium (Gd) and aluminum(Al) plates. The spectra of plasma ions for gadolinium and aluminumtargets are presented at laser radiation energies of 2, 7, 20 J and 1 J, respectively. For the gadolinium target, an increase in the peak amplitudes in ion spectra with increasing influencing radiation energy and manifestations of higher-energy ions are observed. The difference in the ion emission for gadolinium and aluminum targets is also recorded at close radiation energies of 2 and 1 J, respectively.

Due to the possibility of neutron pumping of the active medium formed by Gd¹⁵⁵ and Gd¹⁵⁶ gadolinium isotopes, neutron spectral parameters in the active medium are numerically and theoretically studied. The active medium is placed in a tungsten cylindrical volume. Several versions of a tungsten bulb filled with compact gadolinium oxide with graphite reflectors and without reflectors are considered. It is found that the neutron spectrum in the active medium makes possible population inversion of excitation levels of Gd¹⁵⁶ isotope nuclei at certain combinations of geometrical parameters of the cylindrical volume.