A procedure for separating one- and two-neutron events using the number of active cells and the number and shape of clusters is described. This procedure is effective also in the case of identical neutron energies, when criteria based on time-of-flight information fail. The results of Monte Carlo simulation with the Geant4 toolkit of the interaction of single and pairwise neutrons with energies from 0.5 to 4 GeV in a 16‑layer neutron detector are presented.
An Erratum to this paper has been published: https://doi.org/10.1134/S1547477126040011
The feasibility of allocation of a spectator hadron calorimeter, designed to determine the centrality of collisions, at the NICA collider by using the collider’s magnetic elements is considered. It is shown that the achieved deflection of the proton spectators from the main beam virtually eliminates the ambiguity of the calorimeter data for central and peripheral events.
Various methods to produce Gd-containing nanoparticles (precursors of Gd2O3) were assessed. Their size and morphology are shown to strongly depend on the synthesis technique and composition. The reaction of highly diluted solutions of gadolinium nitrate with ammonium oxalate led to formation of Gd2(C2O4)3 oxalate sol particles with a size of 8 nm in presence of surfactant and 26 nm particles when it was absent. During storage of these sols, the particle size increases to 180–200 nm. Gd(OH)3 particles and Gd2(C2O4)3 particles were synthesized by the sol–gel method. Hydroxide Gd(OH)3 had the morphology of extended broken planes, while oxalate Gd2(C2O4) had the structure of micrometer-sized polyhedra. Subsequent application of SiO2 shells to their surface by the hydrolytic decomposition of tetraethoxysilane led to formation of core–shell particles Gd(OH)3@SiO2 and Gd2(C2O4)3@SiO2, morphologically identical to the Gd(OH)3 and Gd2(C2O4)3 nuclei. Thermal decomposition of Gd(OH)3 and Gd2(C2O4)3 or gadolinium citrate resulted in formation of cubic Gd2O3 particles whose morphology does not depend on that of the precursors.
A mathematical model is formulated to describe the plasma treatment of spent nuclear fuel (SNF) reprocessing wastes, which are fed into an air-plasma flow as dispersed aqueous–salt–organic compositions (ASOCs) containing ethanol or acetone as organic additives. The model describes the coupled kinetics of droplet heating and evaporation, interphase momentum exchange, and heat and mass transfer within a one-dimensional two-phase-flow framework, which is cast in dimensionless form to enable parametric analysis and scale-up. Thermochemical calculations are used to determine optimal ASOC formulations that provide an adiabatic combustion temperature of approximately 1500 K, thereby ensuring energetically efficient plasma operation and complete oxidation of the organic fraction. The influence of key operating parameters—initial plasma temperature and velocity, droplet size and injection velocity, and liquid-to-gas mass ratio—on the spatial extent of droplet evaporation is investigated numerically using a fourth-order Runge–Kutta integration scheme with controlled accuracy. The results show that, at temperatures above about 1500 K, the overall rate of plasma utilization is governed by solvent (water) evaporation, whereas further increases in inlet plasma temperature have only a weak effect on the length of the complete-evaporation zone. In contrast, droplet size and flow hydrodynamics exert a dominant influence: reducing the initial droplet diameter from 100 to 40 μm and decreasing the gas-flow velocity from 90 to 10 m s–1 lead to multi-fold reductions of the evaporation length, allowing complete evaporation within reactor lengths not exceeding 1 m. The resulting model serves as a physically sound and computationally efficient means of forecasting and refining droplet-evaporation dynamics in air-plasma reactors designed for processing wastes from spent nuclear fuel reprocessing and other liquid radioactive waste streams.
