[en] The motional behaviour of hexadecane-h₃₄ within the pseudo-hexagonal channels provided by the urea-d₄ framework has been studied by incoherent quasielastic scattering between 5 K and 370 K. On the instrument time scale (80 μeV), at least two components could be separated, which are attributed to reorientational jumps of the paraffins around their long axes and damped librations, respectively. At 147 K a phase transition takes place involving an orthorhombic deformation of the host channels and a simultaneous change of 60 degrees to 180 degrees jumps. From the activation energy it is concluded that the motional properties of the included molecules are responsible for this transition. (author) 6 refs., 4 figs

[en] Magnetic susceptibility, magnetization and powder neutron diffraction measurements between 300 and 1.5 K have been carried out on synthetic ferrosilite, Fe₂Si₂O₆ (orthorhombic, Pbca) and hedenbergite, CaFeSi₂O₆ (monoclinic, C2/c). Ferrosilite contains zigzag double bands of edge-sharing Fe²⁺ octahedra separated by layers of single silicate chains, which orders antiferromagnetically into a collinear structure at 40 K followed by a spin-canting transition at 8 K. It also shows a spin-flip transition at 45 kOe below T_N. Magnetic susceptibility measurements indicate a Curie Weiss behavior above 50 K with a positive Curie temperature, θp of 30 K. Powder neutron diffraction measurements between 40 and 8 K indicate that all the Fe²⁺ spins are ordered ferromagnetically within one octahedral band, which are antiferromagnetically coupled to neighboring bands, the spin direction being parallel and antiparallel to b. Below 8 K, the spin direction is canted away from the b axis. The Fe²⁺ magnetic moments at the regular octahedral M1 and the distorted octahedral M2 sites at 0 K are 4.3+-0.1 and 3.3+-0.1 μ_B respectively, indicating considerable covalency at the M2 site. Hedenbergite orders antiferromagnetically below 38 K with a positive Curie temperature, θp = 35 K. The magnetic structure is very similar to that of ferrosilite; the spins are in the ac plane 132 degrees away from the c axis. The Fe²⁺ moment at the octahedral M1 at 0 K site is 4.33+-0.04 μ_B. (author) 9 refs., 7 figs

[en] Two independent studies to determine the location of the electron transporter, ubiquinone, and the bacterial antibiotic, gramicidin A, within oriented lipid bilayers of the zwitterionic phospholipid dimyristoylphosphatidylcholine (DMPC), are in progress. The contrast variation technique is used, in addition to information known about the conformation of lipid bilayers, to reconstruct a scattering density profile along the perpendicular to the plane of the bilayer. (author) 4 refs., 6 figs., 1 tab

[en] Short communication

No abstract available

[en] Four-circle diffractometers located on a hot-source beam tube of a steady-state reactor allow crystal structures to be studied at very high momentum transfer (Q > 20 A^-1) to good precision and accuracy. Thus fine details of atomic probability density distributions can be seen, which are important e.g. for the understanding of structural phase transitions or disorder in crystalline materials. The instrumental (beam optics, detectors) and experimental aspects including the corrections applied to the measured intensities are discussed as far as they are specific to hot-source four-circle diffractometry. (author) 31 refs., 3 figs., 1 tab

[en] The internal magnetic field at the nucleus site in iron metal has been calculated from the coherent magnetic neutron scattering data. The field value was found to be -149(1) kOe. It can be compared with the value -333 kOe known from Moessbauer spectroscopy. The difference should be attributed to the contribution of those electrons which do not manifest themselves in magnetic neutron scattering. (author) 4 refs

[en] Elastic, inelastic and quasielastic neutron scattering experiments are performed on natural zeolites. Hydrogen atoms at the water molecules could be located in the fibrous zeolites natrolite and edingtonite. Inelastic neutron spectra can be divided into translational (δE < 40 meV) and librational motion (40 - 100 meV) in the case of harmotome. The analysis of quasielastic scattering in partially dehydrated samples gave diffusion constants of about 8.10^-5 cm sec^-1 at T = 295 K for the full amount of water. (author) 6 refs., 4 figs., 1 tab

[en] Neutron diffraction has turned out to be an effective tool in texture analysis for metal as well as for geological samples. The advantages are mainly due to the low absorption of neutrons by matter, allowing to measure complete pole figures on large, coarse-grained and multiphase samples. The experimental techniques performed on the four-circle diffractometer at the research reactor FRJ-2 in Juelich are described. Examples are given for several metallic specimen and rocks. The forthcoming installation of a position-sensitive detector will highly improve the efficiency of the diffractometer system. Combined with profile analysis methods, texture analyses can be extended to low-symmetry and to multiphase samples. This is of special interest in geosciences. (author) 10 refs., 7 figs

[en] The structure of β'-MoO₃, a new modification of MoO₃, is closely related to the structure of ReO₃ and has been refined using high resolution neutron powder diffraction data and the Rietveld technique. The structure is monoclinic (P2₁/n, a = 7.415(1), b= 7.433(1), c = 7.654(1), A, β = 90.09(2)). β'-MoO₃ is isostructural with the room temperature monoclinic modification of WO₃ and may be derived from the deuterated intercalate (D_xMoO₃), also with ReO₃-type structure, by heating in oxygen at 200 degrees C. The modification is structurally intermediate between the WO₃-type and the thermodynamically stable α-MoO₃. (author) 9 refs., 2 figs., 2 tabs