A. Muzychka

Neutron spectroscopy of water adsorbed on silica

Abstract Computational and real neutron scattering experiments are presented. The computations were performed in a modern cluster approximation, which is used in computational chemistry. The amplitude-weighted densities of the vibrational states for a few models of the water molecule depositions at the surface are obtained. The results are in good agreement with the experimental inelastic neutron scattering spectra.

Neutron scattering from water adsorbed on ultrafine nickel particles

Abstract A modified NDDO method is applied to the Ni cluster calculations. The calculated amplitude-weighted density of vibrational states spectrum for (Ni 11 +H 2 O) clusters fits the experimental inelastic neutron scattering spectrum obtained at 80 K well for highly dispersed Ni particles covered with water.

Water on amorphous silicas: INS study

Abstract A comparative INS study of the vibrational spectra of the water adsorbed on three dispersed amorphous silicas(aerosil, silica gel and aerogel) is presented. The spectra have been obtained as differences between the spectra of the “as-prepared” air-dry samples and the air-dried ones. The spectra of the adsorbed (a) and/or retained water are separated. the a-water spectra in the above three cases are substantially different indicating the different configurations of the sample surface active centers. This phenomenon is suggested to be caused by the polymorphism of the “as-prepared” material cores, due to the polymerization peculiarities when manufacturing the products by different technologies.

Search for low-energy upscattering of ultracold neutrons from a beryllium surface

We present results of a search for anomalous low-energy upscattering of ultracold neutrons from a beryllium surface. This upscattering is considered one for the possible reasons for UCN “disappearance” from very cold beryllium bottles, as observed in experiments. The indium foil activation method was used to measure a very low intensity flux of upscattered UCN. The (15–300) m/s velocity range of upscattered UCN is ruled out by these measurements at a confidence level of 90%.

Monte Carlo simulation of nonstationary transport of ultracold neutrons in horizontal neutron guides and the storage of ultracold neutrons

Abstract The results are presented of a Monte Carlo simulation of nonstationary transport of ultracold neutrons (UCNs) in straight and curved neutron guides of rectangular cross section for different suppositions about the losses and the character of diffuse neutron scattering by imperfectly smooth reflecting surfaces. The storage of UCNs in experimental chambers is modelled for the case of a low periodic or aperiodic pulse neutron source for production of UCNs.

Search for anomalous transmission of ultracold neutrons through metal foils

Results are presented on the search for anomalous transmission of ultracold neutrons (UCNs) through beryllium (thickness ∼0.14 mm), stainless steel (0.05 and 0.015 mm), and copper (0.01 and 0.018 mm) foils. This anomalous transmission is considered to be a possible reason for the disappearance of UCNs from beryllium bottles, an effect which was discovered in experiments at the St. Petersburg Nuclear Physics Institute and which was recently observed in the experiment of V. E. Varlamov et al., JETP Lett. 66, 336 (1997). No transmission was found in our measurements at the 10−7 level except in the case of copper foils, which we attribute to the presence in the UCN flux of an admixture of neutrons with energies higher than the boundary energy for copper.

Monte Carlo simulation of the nonstationary transport of very cold and ultracold neutrons in vertical neutron guides and the storage of ultracold neutrons

Abstract The results are presented of Monte Carlo simulation of the transport of very cold (VCN) and ultracold neutrons (UCN) in straight and curved vertical neutron guides with a rectangular cross section in the presence of neutron losses due to neutron capture and diffuse scattering on imperfectly smooth reflecting surface of the guides wall. The gravitational neutron deceleration and bending of neutron trajectories are rigorously taken into account. The nonstationary storage of UCN in experimental chambers is modelled for a low periodic or a periodic pulse neutron source.

Density of vibrational states of thiol capped CdS particles. Inelastic neutron scattering

Abstract Colloidal semiconductor species are currently under intense investigation as examples of nonmolecular materials that demonstrate a quantum confinement effect [1]. The species particle size is a few nanometers, so surface atoms constitute a significant part of the materials and the interface between the particle core and the surrounding effects greatly their properties. An INS study of the surface zone vibrations is presented.

Neutron spectroscopic study of crystalline electric-field in infinite-layer Sr1−xNdxCuO2

Abstract Inelastic neutron scattering has been employed to search for the crystalline-electric-field (CEF) transitions in the infinite-layer (IL) Sr 1−x Nd x O 2 compounds produced by high-pressure technique. For the first time we have been able to observe the complete energy spectrum of the ground state J-multiplet of Nd 3+ in the IL phase and to determine the CEF parameters. Dependence of the CEF splitting on Nd doping is discussed.

Neutron diffraction and neutron spectroscopic studies of crystalline electric field in AlSr2LnCu2O7 (Ln = Y, Er, Ho)

Abstract Investigation of the substitution effects for various sites in the perovskite-like systems with a general formula M1(Sr, Ba)Ln(Cu, M2)O (M = Bi, Tl, Hg, Al, Ga, Zn, Ni and Ln = rare earth) is of great interest in connection with the problem of high-Tc superconductivity. The 1212 AlSr2LnCu2O7 (Ln = rare earth) compounds, non-superconducting insulating structural analog of the 123 LnBa2Cu3Ox superconductors, exhibit unusual magnetic properties resulting from an interaction between Cu magnetic moments within the CuO2 planes and the rare-earth subsystem. To obtain precise information on the crystal structure neutron powder diffraction measurements have been performed for the 1212 AlSr2LnCu2O7 − x (Ln = Y, Er, Ho) compounds. Inelastic neutron scattering has been employed to search for the crystalline-electric-field (CEF) transitions in these compounds. The observed CEF spectra are discussed in terms of the structural model which involves locally inhomogeneous oxygen distribution in the basis planes.