Raman and Neutron Scattering Study of Partially Deuterated L‐Alanine: Evidence of a Solid‐Solid Phase Transition

Raman and neutron experiments using specific isotope labeling were combined in order to study the dynamics and structure of L ‐alanine. Inelastic neutron and Raman scattering data of C₂H₄(ND₂)CO₂D are discussed in relation to the doubling of the lattice parameter a observed by means of neutron powder diffraction in C₂D₄ (NH₂)CO₂H. The major changes accompanying the phase transition are found in the vibrational frequencies involving the torsional vibration τ(CO₂^?), which is clearly affected by the hydrogen bonds between the protons of the ammonium group and the oxygen atoms of the carboxylate group. At lower temperatures the rearrangement of identifiable hydrogen bonds induces changes in the bending vibration δ(ND₃), confirming some orientational disorder.     

Inelastic neutron scattering spectra of the hydrogen tungsten bronze H0.4WO3

Inelastic neutron scattering spectra of metallic H_0.4WO₃ show only the vibrations that would be expected of a metal hydroxide. The diffusion coefficient of the proton could not be detected from quasi-elastic scattering with the best available neutron spectrometer setting an upper limit to its value of 10^?7 cm²/sec. Both these results confirm that this material is correctly described as a hydroxide.     

Mutual interactions in a ternary protein/bioprotectant/water system

The dynamics of hydration water play a key role in many biological processes. The activity and function of proteins are strongly affected by the presence of water, which interacts primarily by means of hydrogen bonding. These interactions are examined in this work by a comparison of neutron vibrational spectra (Inelastic Neutron Scattering, INS) of dry lysozyme and hydrated lysozyme at h = 0.7 (g of H₂O/g of protein) with those of a lysozyme/water mixture at the same hydration value in the presence of the glass-forming bioprotectant trehalose. A difference spectrum, obtained by subtracting the dry lysozyme spectrum from that of the lysozyme/water mixture, yields the hydration water spectrum which is compared to the INS spectra of different kinds of ice in order to determine the changes induced by lysozyme on the hydrogen-bonded network of water. An additional comparison is performed by using a double-difference spectrum obtained by subtracting both the dry lysozyme and the trehalose spectra from the lysozyme/trehalose/water ternary spectrum. The effects of the mutual interactions among the three components, i.e. protein, disaccharide and water, are determined by comparison of the spectra of the dry systems (lysozyme, trehalose) with the difference spectra obtained from subtraction of the dry systems from the binary systems. It is concluded that the interfacial water more strongly affects the intermolecular mode region at low frequencies, whereas the vibrational spectra at high frequencies are more influenced by lysozyme and trehalose.     

CO2 diffusivity in LiY and NaY faujasite systems: a combination of molecular dynamics simulations and quasi-elastic neutron scattering experiments

Quasi-elastic Neutron Scattering combined with Molecular Dynamics simulations have been carried out to gain further insight into the CO₂ dynamics in LiY and NaY Faujasites. In both materials, it was pointed out that the transport diffusivity (D_T) increases with the loading whereas the self diffusivity (D_S) decreases. In addition, it was shown that LiY exhibits a significant slower CO₂ self diffusivity process due to a strong interaction between the Li⁺ cation and the adsorbate molecules at the initial stage of diffusion. This result is consistent with higher simulated activation energy in this cation exchanged faujasite form. By contrast, the transport diffusivity is revealed to be slightly faster in LiY than in NaY.     

Characterisation and determination of the neutron transmission properties of sodium–calcium and sodium borates from different regions in Turkey

In this study, ulexite, probertite found within sodium–calcium borates and borax, and tincalconite found within sodium borates retrieved from different regions in Turkey are evaluated for their neutron irradiation performances. Characterisations were performed using XRD, FT-IR, Raman spectroscopy. B₂O₃ contents were determined experimentally, structural water contents and surface morphologies were determined using DTA/TG and SEM. Neutron transmission values and total macroscopic cross-sections were determined using ²³⁹Pu–Be source moderated in a howitzer. Neutron transmission values from lowest to highest were found to be as follows: secondary ulexite (K?rka), tincalconite (K?rka), ulexite (Kestelek), ulexite (K?rka), borax (K?rka), probertite (Kestelek) and ulexite (Bigadiç).     

Sorption and Diffusion of SF6 in Silicalite Crystals

Kinetic and equilibrium data for sorption of SF₆ in silicalite have been determined by the ZLC method. The equilibrium constants and adsorption energy are comparable with the values reported previously for SF₆-NaX. Intracrystalline diffusion is relatively rapid with diffusivities of order 10_–7– 10^–8 cm²·s^–1 at temperatures in the range 30–90°C. The implications for the use of SF₆ as a probe molecule for assessing the integrity of silicalite membranes are considered.     

Abstandsvergleich M–H/M–D aus Röntgen‐ und Neutronenbeugungsdaten am Beispiel von Na3Rh(H/D)6

Comparison of the Distances M–H/M–D from X‐Ray and Powder Neutron Scattering Data on the Example of Na₃Rh(H/D)₆ Mixtures of NaNH₂, NaN₃ and Rh heated to 600 °C in autoclaves for salt melts show no indication of formation of ternary nitrides, but unexpectedly single crystals of a ternary hydride, Na₃RhH₆, were obtained. These crystals were isolated by washing the reaction product with liquid ammonia at room temperature. During this procedure metallic sodium – formed by decomposition of both the amide and the azide at elevated temperatures – is removed. X‐ray diffraction measurements on single crystals of Na₃RhH₆ allowed to even refine the displacement parameters of the hydrogen atoms and to compare the obtained results with data from powder neutron scattering of Na₃RhD₆ published by Bronger, Gehlen and Auffermann [1]. Only little differences are found between the lattice parameters, atomic positions and, noteworthy, the resulting distances Rh–H and Rh–D, respectively.     

Large-sample neutron activation analysis: Present status and prospects

Neutron activation analysis is attractive for trace-element determinations in large samples. Facilities for reactor irradiation and -ray spectrometry of kilogram-size cylindrical samples are described. The thermal neutron flux is ca. 5·10¹²m^–2·s^–1 with a _th/ _epi>10⁴, so neutron self-thermalization can be neglected. The correction for the neutron attenuation within the sample is derived from measurement of the neutron flux depression just outside the sample. Correction for -attenuation in the sample is performed via linear attenuation coefficients derived via transmission measurements. Also the natural radioactivity in the sample is taken into account. Examples are given of materials to which large sample INAA has been applied successfully, and further lines of development and exploration are indicated.     

Methyl rotation in polydimethylsiloxane studied by neutron transmission

Neutron transmission of polydimethylsiloxane has been measured as a function of neutron wavelength in the range 4–10 Å, at room temperature. Scattering cross sections per hydrogen atom have been obtained and the slope (12.2 ± 0.2) barns/Å has been derived. Comparison with calibration curves relating the slope to the barrier hindering internal rotation as well as comparison with calculated neutron cross sections using the Krieger–Nelkin formalism for different dynamical situations indicates practically free rotation of CH₃ groups about their C₃ symmetry axes.     

Neutron spectrum parameters in irradiation channels of the Nigeria Research Reactor-1 (NIRR-1) for the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-NAA standardization

Summary The first nuclear research reactor in Nigeria has been commissioned for neutron activation analysis and limited radioisotope production. In order to extend its utilization to include the k₀-standardization method, the following neutron spectrum parameters in inner and outer irradiation channels were determined by the “Cd-ratio for multi-monitor method”: the thermal-to-epithermal flux ratio, f, and the epithermal flux shape factor, α. Neutron spectrum parameters determined in the inner irradiation channel B2, are: α = -0.052±0.002 and f = 19.2±0.5. For the outer irradiation channel B4, the neutron spectrum parameters were found to be α = +0.029±0.003 and f = 48.3±3.3. The results are compared with the neutron spectrum parameters of other reactor facilities with similar core configuration such as the Slowpoke and Miniature Neutron Source Reactor facilities available in the literature.     

Neutron activation analysis of the dissolution ofn-GaAs in 1M KOH

The dissolution ofn-GaAs in 1M KOH has been investigated using neutron activation analysis. For this purposen-GaAs electrodes were irradiated with thermal neutrons. Neutron irradiation induced defects were annihilated by annealing. The corrosion measurements were performed in the plateau region of the photocurrent in 1M KOH with and without Fe(CN) ₆ ^4– and at rest potential in the dark (currentless) in the presence of Fe(CN) ₆ ^3– . We could prove the hole injection of Fe(CN) ₆ ^3– inton-GaAs and the lowering of the photocorrosion due to the presence of Fe(CN) ₆ ^4– .     

Location and Vibrations of Hydrogen in La2C3H1.5

We report on the incorporation of hydrogen into La₂C₃ and on the characterisation of its position. Temperature‐dependent X‐ray investigations show that the hydrogenation process is reversible and the product La₂C₃H_1.5 is amorphous. In principle, IR and Raman spectroscopies can provide some structural information, but in the present study, they are of only limited value. Inelastic neutron scattering (INS) has advantages for measuring the H‐vibrations in La₂C₃H_1.5 and these are compared with the results of molecular dynamics simulations. A structural model based on published pair‐potentials predicts that hydrogen (or deuterium) occupies the “tetrahedral” holes in the lanthanum sublattice. This model also accounts for the observed vibrational spectra.     

Measurements of fast neutron capture cross sections on <Superscript>63</Superscript>Cu and <Superscript>186</Superscript>W

Neutron capture cross sections on ⁶³Cu and ¹⁸⁶W were measured by fast neutron activation method at neutron energies from 1 to 2 MeV. Monoenergetic fast neutrons were produced by ³H(p,n)³He reaction. Neutron energy spread by target thickness, which was assumed to be the main factor of neutron energy spread, was estimated to be 1.5% at neutron energy of 2.077 MeV. Neutron capture cross sections on ⁶³Cu and ¹⁸⁶W were calculated by reference comparison method on those of ¹⁹⁷Au(n,γ). Not only statistical errors of gamma-counts from samples but also systematic errors in the counting efficiency for HP Ge detector and the uncertainty of areal density of samples were considered in calculating neutron capture cross section. Estimated neutron capture cross sections on ⁶³Cu and ¹⁸⁶W were also compared with ENDF-6 data.     

Measurement of30Si as a tracer by neutron-induced prompt gamma-ray analysis

The application of stable isotope analysis using neutron-induced prompt -ray analysis (PGA) with cold/thermal neutron beams for the tracer study of geological materials are discussed. Silicon has three natural isotopes differing in abundance:²⁸Si (92.23%),²⁹Si (4.67%) and³⁰Si (3.10%). For the purpose of the assessment of Si migration in engineered barrier material, enriched³⁰Si can be used as a tracer due to its nuclear and chemical properties. Isotope analysis of³⁰Si was performed by PGA during the tracer study. Neutron intensity at the sample position was 1.4·10⁸ n¢cm^–2·s^–1, 2.4·10⁷ n·cm^–2·s^–1 for cold and themal neutron guided beams of JRR-3M, respectively. Calibration curves and analytical sensitivity of³⁰Si were determined based on measurement of standard samples. BG and detection limits for³⁰Si analysis were also measured in Japanese bentonite (Kunigel V1 and Kunipia F) and their pore water. Fiffteen elements were determined simultaneously using PGA.     

FTIR-ATR spectroscopic analysis of bis-crown ether based PVC-membranes

Summary In order to get more information about the complexation reaction between potassium-selective electrode membranes and aqueous solutions of KCl, KSCN, NaCl, NaSCN, NH₄Cl and NH₄SCN, model membranes have been analyzed by the molecular-specific surface technique Attenuated Total Reflection (ATR) in the infrared region, thus providing an information depth between 0.1 and 3 m depending on the angle of incidence of the radiation. The membranes have been prepared by dissolving PVC, dioctylsebacate and crown ether BME-44 in differing amounts in THF and casting in a glass ring on a glass plate. It has been found that DOS is slightly enriched at the surface but the membranes are sufficiently stable. It has further been found that complex formation occurs in the surface region for SCN^– as well as Cl^–. Pretreated and subsequently rinsed samples have shown that Cl^– is almost totally washed away. But in the case of the lipophilic SCN^–1 anion, this diffuses into the bulk; rinsing results in a loss at the near-surface region only. A special diffusion experiment, in which only one side of the membrane was in contact with the solution, has shown that diffusion of KSCN through the membrane occurs at a very low rate with a diffusion constant of appr. 10^–8 cm²/s.For better understanding of the transport phenomena in situ measurements will be carried out.

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FTIR-ATR-Spektroskopische Analyse von Bis-Kronenether-PVC-Membran-Oberflächen.II. Diffusionsverhalten von K⁺-Komplexen im System PVC/Dioctylsebacat/Kronenether BME-44. Ex-situ-Untersuchungen an getrockneten Membranen

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Part I, see [1]     

Determination of the 209Bi(n,γ) capture cross section at a cold neutron beam

Summary The total capture cross section of ²⁰⁹Bi was determined at the cold neutron beam PGAA-NIPS facilities at the Budapest Neutron Centre. The measurements were performed using a coaxial HPGe detector with Compton suppression. The total and partial gamma-ray production cross sections were deduced relative to the ¹⁴N(n,γ) partial gamma-ray production cross section. By using a bismuth nitrate stoichiometric compound as the sample, we excluded various systematic uncertainties. The total capture cross section is in very good agreement with the compilation of Mughaghab, but is slightly lower than the most recent value determined at the high flux reactor of the ILL in Grenoble, France. We also performed measurements using a 0.5 mm thin Bi metal disc. The relative intensities determined from the Bi disc and the compound samples are in good agreement.     

Neutron captue prompt gamma-ray activation analysis at the NIST Cold Neutron Research Facility

An instrument for neutron capture prompt gamma-ray activation analysis (PGAA) has been constructed as part of the Cold Neutron Research Facility at the 20 MW National Institute of Standards and Technology Research Reactor. The neutron fluence rate (thermal equivalent) is 1.5·10⁸ n ·cm^–2·s^–1, with negligible fast neutrons and gamma-rays. With compact geometry and hydrogen-free construction, the sensitivity is sevenfold better than an existing thermal instrument. Hydrogen background is thirtyfold lower.     

Transport characterisation of a PIM system used for the extraction of Pb(II) using d2ehpa as carrier

The facilitated transport of lead(II) through polymeric inclusion membranes consisting of cellulose triacetate as polymeric support, bis-(2-ethylhexyl)-phosphoric acid (d2ehpa) as carrier, and tris-(2-butoxyethyl)phosphate as plasticiser (tbep), is investigated. The influence of some of the aqueous and membrane components on the permeability of Pb(II) was studied. The maximum flux obtained with these membranes is 3.5×10⁻⁶ mol m⁻² s⁻¹, which is of the same order of magnitude of those reported for supported liquid membranes and is in the upper range of those reported for polymeric inclusion membranes. Aqueous and membranes resistances were determined from a model that describes the transport mechanism across the membranes using the stoichiometric relationship and the extraction equilibrium constant value of 6.2×10⁻⁴ determined independently by solid–liquid extraction. An activation energy of 11 kJ mol⁻¹ was also determined for Pb(II) migration, which suggest that the transport of Pb(II) is controlled by a membrane diffusion mechanism. Membrane characterisation was performed using several techniques including atomic force microscopy, scanning electron microscopy coupled with energy-dispersive spectroscopy, and thermal analysis.     

Cold neutron prompt gamma activation analysis at NIST: A progress report

An instrument for prompt gamma-ray activation analysis is now in operation at the NIST Cold Neutron Research Facility (CNRF). The cold neutron beam is relatively free of contamination by fast neutrons and reactor gamma rays, and the neutron fluence rate is 1.5·10⁸ cm^–2·s^–1 (thermal equivalent). As a result of a compact target-detector geometry the sensitivity is better by a factor of as much as seven than that obtained with an existing thermal instrument, and hydrogen background is a factor of 50 lower. We have applied this instrument to multielement analysis of the Allende meteorite and other materials.     

Inelastic neutron scattering spectra of alkali metal (Na,K) bifluorides: The harmonic overtone of v3

Inelastic neutron scattering spectra of MFHF (M  Na and K) have been measured up to energy transfers of ca. 4000 cm^?1 Both 0 → 1 and 0 → 2 transitions of the bending (v₂), and antisymmetric stretching (v₃) modes were observed. A normal harmonic (i.e. no quartic contribution) model for the dynamics of the bifluoride ion is entirely consistent with our observations. Evidence of phonon dispersion was observed in the band shape of v₃, but no structure attributable to the LO mode could be found. The similarity of the band shapes of v₃ for both NaFHF and KFHF is interpreted in terms of a very short range coupling mechanism.