Revisiting UF6, NpF6 and PuF6 for bonding and molecular surface analysis within density functional theory: Comparative study at the different theory levels with the same basis set

UF6, NpF6 and PuF6 have been reexamined for their bonding characteristics and molecular surfaces. The bonding properties of these compounds were analyzed by calculating bond orders, partial charges, dipole moments, localized molecular orbitals, and topological properties. The bond orders increase with the atomic number (Z) of actinide as the bond lengths decrease. The partial charges, calculated by Atoms in Molecules (AIM) and Mulliken methods, and the bond dipole moment decrease with increasing Z. There is a fluctuation in the partial charge value for Np according to other charge models. The f character of the localized molecular orbital increases with Z. In general, the parameters obtained from topological analysis show an increase in the covalency across the period for U, Np and Pu. The molecular volume and surface obtained from surface analysis decrease with Z, which is consistent with the bond lengths. The molecular surface electrostatic potentials for intermolecular interactions decrease with Z according to surface analysis. The mass density and heat of sublimation data are interpreted based on molecular surface analysis results. All the density functionals and HERDB with the same basis set give consistent results for almost all the quantities calculated

Monte Carlo calculation of the de-excitation of fission fragments of Cf-252(sf) within multimodal random neck rupture model

The multimodal random neck rupture model has been employed to study the energy distribution in nuclear fission. Monte Carlo calculations have been carried out on the de-excitation of fission fragments of Cf-252(sf) using this model. In this study special attention has been paid to the law of conservation of energy. Results for the neutron multiplicities and kinetic energies, average gamma energies are in good agreement with the experimental data. Mass and charge distributions of secondary fission fragments are also well reproduced in the calculations

Possible exit channel effect on isomer yield ratios

Isomer yield ratio measurements in fission are important in understanding the fission process. With the development of new instrumental techniques, a large number of yield data are now available. The experimental data on isomer yield ratios in the thermal neutron induced fission of U-235 compared with those calculated from the simple statistical model by MADLAND and ENGLAND. The method of calculation has been extended to the isotopes having more than one isomeric state. The results may be explained according to the multi-exit-channel model of fission

Ternary particle yields in Cf-249(n(th),f)

An experiment measuring ternary particle yields in Cf-249(n(th),f) was carried out at the high flux reactor of the Institut Laue-Langevin using the Lohengrin recoil mass separator. Parameters of energy distributions were determined for 27 ternary particles up to Mg-30 and their yields were calculated. The yields of 17 further ternary particles were estimated on the basis of the systematics developed. The heaviest particles observed in the experiment are Si-37 and S-37; their possible origin is discussed