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We propose to perform the first measurement of the neutron–neutron scattering cross section in the through-channel of the pulsed aperiodic reactor YAGUAR (Snezhinsk, Russia). Such a measurement directly determines the neutron–neutron scattering length, and by comparison with the proton–proton scattering length bears upon the issue of charge symmetry of the nuclear force. The proposed experimental set-up, as well as modelling of the neutron density and of the frequency of neutron–neutron collisions is described. Experimental results are reported on the formation and optimization of the thermal neutron field inside the through-channel of the reactor YAGUAR. The instantaneous value of 1.1 × 1018 cm−2 s−1 obtained for the thermal neutron flux density is large enough to perform the first direct neutron–neutron scattering length measurement.

inTiO 2 /Ni metal-semiconductor composites were prepared from mesoporous titanium dioxide obtained by sol-gel precipitation in the presence of a structure-forming template. The photocatalytic activity of mesoporous TiO 2 /Ni composites in the generation of hydrogen from aqueous ethanol mixtures was discovered and studied in detail.The high activity of titanium dioxide as a photocatalyst in the redox reactions of many substrates has stimulated research on the development of the controlled synthesis of TiO 2 samples possessing given texture, phase state, and optical and electrophysical characteristics [1][2][3][4][5]. The photocatalytic activity of titanium dioxide was found to be very sensitive to particle size, crystallinity, and phase composition. We should note that powdered titanium dioxide photocatalysts commonly used in most redox reactions, as a rule, have a relatively small specific surface. A significant factor lowering the activity of such catalysts is the relatively low rate of reactions involving electrons of the TiO 2 conductance band in the absence of catalysts for the secondary "dark" steps featuring noble metals such as Pt [1, 2], Rh [1, 2], Pd [1, 3], Ag [1, 6], and Au [7] on the surface of the photocatalyst or an inert support. Hence, there are two directions for improving TiO 2 photocatalytic systems. The first direction involves the development of methods for the preparation of highly porous titanium dioxide samples (especially, mesoporous samples) with surface greater than 100 m 2 /g available for interaction with substrate molecules, ordered porous structure, and high content of anatase, which is the structural modification of TiO 2 most active in photocatalytic reactions. The second direction involves the development of composites, especially metal-semiconductor composites, in which a high degree of separation of the charges generated in the semiconductor may be achieved due to close electronic contact between the composite components and the use of these electrons in the reaction with adsorbed substrates.In the present work, both these approaches are followed for the development of the direct synthesis of a highly active mesoporous TiO 2 /Ni composite photocatalyst by the photoreduction of a nickel salt adsorbed on the mesoporous titanium dioxide surface. The photocatalytic properties of this composite in the generation of hydrogen from aqueous ethanol mixtures were studied.Samples of mesoporous titanium dioxide were obtained by sol-gel hydrolysis of Ti(IV) tetrabutoxide in 1-butanol by atmospheric moisture in the presence of a structure-forming template, namely, dibenzo-18-crown-6. After completion of the 26 0040-5760/05/4101-0026