Small-angle neutron scattering from micellar solutions

Micellar solutions are the suspension of the colloidal aggregates of the sur-factant molecules in aqueous solutions. The structure (shape and size) and the interaction of these aggregates, referred to as micelles, depend on the molecular architecture of the surfactant molecule, presence of additives and the solution conditions such as temperature, concentration etc. This paper gives the usefulness of small-angle neutron scattering to the study of micellar solutions with some of our recent results.     

Small-angle neutron scattering studies of nonionic surfactant: Effect of sugars

Micellar solution of nonionic surfactantn-dodecyloligo ethyleneoxide surfactant, decaoxyethylene monododecyl ether [CH₃(CH₂)₁₁(OCH₂CH₂)₁₀OH], C₁₂E₁₀ in D₂O solution have been analysed by small-angle neutron scattering (SANS) at different temperatures (30, 45 and 60° C) both in the presence and absence of sugars. The structural parameters like micelle shape and size, aggregation number and micellar density have been determined. It is found that the micellar structure significantly depends on the temperature and concentration of sugars. The micelles are found to be prolate ellipsoids at 30° C and the axial ratio of the micelle increases with the increase in temperature. The presence of lower concentration of sugar reduces the size of micelles and it grows at higher concentration of sugar. The structure of micelles is almost independent of the different types of sugars used.     

Small-angle neutron scattering from Pb and 238U between 0.6 and 2.2 MeV

Differential cross sections for neutrons scattered from natural Pb and 99.9 % isotopically pure ²³⁸U have been measured at 0.5°, 1.0°, and 1.5°. A neutron energy continuum was produced by bombarding a thick natural lithium target with a 4 MeV, nanosecond-pulsed proton beam. Neutron energies were determined by time-of-flight techniques. Flight paths from the neutron source to the scatterer and from the scatterer to the detector were each about 5 m. For the 0.5° measurements an annular detector geometry with an angular resolution of ± 0.1° was developed to maximize detection solid angle. Data were averaged over 100 keV intervals from 0.6 to 2.2 MeV and were corrected for backgrounds, multiple scattering and inelastic scattering. Measured cross sections were compared to optical-model calculations which included electromagnetic interactions of neutrons with the nuclear Coulomb field. Inclusion of an induced neutron electric dipole moment interaction was not warranted by the data. The angular dependence of the cross section was fitted with a function $\text{A + B}\text{cot}{}^2\text{case1}\text{2}$θ at each energy. Mean values of B for ²³⁸U are in agreement with theoretical predictions. Values of B for Pb are apparently 15 % too low.     

Small-angle scattering and a lower bound for the scattering amplitude at large angles

A relationship is established between the lower bound for the large-angle scattering amplitude and the behaviour of the diffraction and of the backward scattering peak widths.     

Two-dimensional spatially ordered Al2O3 systems: Small-angle neutron scattering investigation

The structure of anodized aluminum oxide films has been investigated by the small-angle neutron scattering method. A theoretical solution is obtained for describing neutron scattering from the Al₂O₃ ordered porous structure. Analysis of the neutron-experiment data shows the possibility of obtaining porous membranes with ideally periodic hexagonal packed pores on a large area (～0.5 cm²).     

Transition from unilamellar to bilamellar vesicles induced by an amphiphilic biopolymer

We report some unusual structural transitions upon the addition of an amphiphilic biopolymer to unilamellar surfactant vesicles. The polymer is a hydrophobically modified chitosan and it embeds its hydrophobes in vesicle bilayers. We study vesicle-polymer mixtures using small-angle neutron scattering (SANS) and cryotransmission electron microscopy (cryo-TEM). When low amounts of the polymer are added to unilamellar vesicles of ca. 120 nm diameter, the vesicle size decreases by about 50%. Upon further addition of polymer, lamellar peaks are observed in the SANS spectra at high scattering vectors. We show that these spectra correspond to a co-existence of unilamellar and bilamellar vesicles. The transition to bilamellar vesicles as well as the changes in unilamellar vesicle size are further confirmed by cryo-TEM. A mechanism for the polymer-induced transitions in vesicle morphology is proposed.     

Small-angle neutron scattering study of the nano-sized features in an oxide dispersion-strengthened Fe12Cr alloy

Small-angle neutron scattering experiments, along with positron lifetime measurements and transmission electron microscopy observations, were performed on samples of an oxide dispersion-strengthened (ODS) Fe12Cr alloy and its non-ODS counterpart in order to characterize their nano-sized features. The nuclear and magnetic scattering data were analysed using the maximum entropy approach for obtaining the size distribution of the scattering centres in these materials. The positron annihilation results and the TEM information have made possible an interpretation of the volume distribution of the scattering centres having sizes below ~16 nm and their proper quantitative analyses. The smaller scattering centres in the ODS alloy exhibit distributions with modal values at ~6–7 and 12–14 nm. The peak at ~6–7 nm appears to be due to the overlapping of more than one type of scattering centres, while the one at ~12–14 nm can be exclusively attributed to the Y-rich centres. The quantitative analysis of the magnetic scattering data yields a volume fraction and number density of the Y-rich particles estimated in 0.70?±?0.03% and 0.77 × 10²² m^?3, respectively.     

An improved method for determination of radiated sound power and sound transmission from large sources

The proposed method is an improvement of the methods for measurement of sound power level, in which the real sound source is represented by an equivalent monopole. It is based on a new concept, the equivalent acoustical centre, which is introduced and defined in the paper. The main assets of the method in comparison with the existing monopole-methods are a higher accuracy, a possibility of measuring at considerably shorter distances from the noise source, and a certain freedom in the choise of the measuring points around the source. Moreover, since the position of the equivalent monopole is obtained, it can be used for more accurate calculations of the sound transmission to the surroundings of the source. The method is particularly suitable for determination of sound power levels and sound transmission of noise radiated from large areas, such as industrial complexes, installations of petrochemical industries and the like. It can be especially useful in disputable cases of industrial plants that produce noise close to the legally permissible limit. The new method was first reported at the meeting of the Dutch Acoustical Society which took place in Utrecht on 22 November 1978.     

Diffuse neutron scattering from an ω-phase ZrNb alloy

A back-scattering neutron spectrometer with an energy resolution of ～2μeV (FWHM) has been used to measure the diffuse quasielastic scattering from the ω-phase of Zr_1-xNb_x (0.18 < x < 0.19). It is found that the intrinsic energy-width of the scattering does not change between room temperature and 1000 K. At both temperatures the width is less than ～0.2μeV and consistent with zero.     

A possible experimental observable for the determination of neutron skin thickness

The dependence between neutron skin thickness and neutron abrasion cross section （σnabr） for neutron-rich nuclei is investigated within the framework of the statistical abrasion ablation model. Assuming that the density distributions for proton and neutron are of Fermi-type, and adjusting the diffuseness parameter of neutron density distribution in the droplet model, we find out the good linear correlation between the neutron skin thickness and the abrasion cross section σnabr for neutron-rich nuclei. The uncertainty of neutron skin thickness determined from σnabr is very small. It is suggested that σnabr can be used as a new experimental observable to extract the neutron skin thickness for neutronrich nucleus. The scaling behaviours between neutron skin thickness and σnabr, separately, for isotopes of ^26-35Na, ^44-56Ar, ^48-60Ca, ^67-78Ni are also investigated.     

从散射谱反演颗粒尺寸分布的测试方法改进

针对从散射谱反演颗粒尺寸分布测量中,由于衍射近似要求近前向取值而带来的反演噪声问题,提出了一种改进的方法.在Chin-Shifrin(C-S)积分变换反演中,插入一种调节函数使得噪声基本消失,又不至于影响反演谱的分布峰位置.对理想单分散颗粒群的模拟效果说明了该法的可行性.对以线阵CCD为接受器件的实验测量和反演结果显示...     

Elastic neutron scattering from 40Ca for neutron energies to 2 MeV

Total and differential elastic neutron scattering cross sections for Ca are analysed for resonance parameters below 2 MeV. A detailed reproduction of the total neutron cross section up to 1.2 MeV is given with multilevel R-matrix formulas. Using the theoretical expressions of Blatt and Biedenharn, shape features of the scattering data versus angle have been explored for spin and parity assignments. Strength functions and average level spacings are determined for s-, p- and d-waves. Reduced widths and the R∞ coefficients have been obtained from the analysis. Using these quantities and the sum rules, the intermediate coupling picture of Lane, Thomas and Wigner is applied to the study of s-, p- and d-wave strength in the energy region up to 2 MeV above the neutron threshold energy.     

Small-angle neutron scattering study of the mesostructure of bioactive coatings for stone materials based on nanodiamond-modified epoxy siloxane sols

The structure formation of sol-gel-derived epoxy siloxane compositions with different ratios of the main precursors (R _{TEOS/EPONEX 1510} = 16/38, 27/27, 38/16 wt %) and with different concentrations of detonation synthesis nanodiamonds (c _DND = 0.05, 0.10, 0.20 wt %) has been investigated using small-angle neutron scattering (SANS). Based on the SANS data, it has been revealed that the synthesized epoxy siloxane xerogels are systems with a two-level fractal structure, in the formation of which the siloxane component plays a dominant role. It has been found that the fractal dimension D _m2 and the radius of gyration R _g2 of clusters in the epoxy siloxane compositions decrease with an increase in the content of the siloxane component. It has been established that the introduction of small additions of detonation synthesis nanodiamonds (less than 1 wt %) into the epoxy siloxane composition with an equal ratio of the main precursors R _{TEOS/EPONEX 1510} = 27/27 wt % leads to a transition from the two-level to three-level structure organization and affects the fractal dimension D _m and the radius of gyration R _g of the formed clusters.     

Structural study of nanoporous carbon produced from polycrystalline carbide materials: Small-angle x-ray scattering

An x-ray small-angle scattering study is reported of the structure of nanoporous carbon prepared by chlorinating carbide compounds having different crystal structures (SiC, TiC, Mo₂C). The measurements were carried out both in reflection and transmission. The angular dependences of the scattering intensity obtained are treated as a result of scattering from nanoparticles of different size. By unfolding the experimental curves into components corresponding to particles with different gyration radii R _g, scatterer distribution functions in gyration radius m(R _g) were found. It is shown that, irrespective of the type of the starting carbide, particles with R _g～5 Å make up the largest fraction in porous carbon. Samples prepared from different carbides differ in the degree of nanoparticle uniformity in size. The most uniform in size are nanoparticles in the samples prepared from SiC, in which the average value R _g ^av <6 Å. Nanoparticles in the porous carbon produced from Mo₂C are about twice larger.     

Small-angle polarized neutron scattering study of spherical Fe16N2 nano-particles for magnetic recording tape

We have performed small-angle polarized neutron scattering experiments of spherical Fe₁₆N₂ nano-particles, which are potential candidate materials for high density magnetic recording tape. The results were analyzed based on a core-shell model, and we evaluated the magnetic structure of the particles. The correlation between the magnetic structure and magnetic stability of the particles were discussed in terms of high density recordings.     

Thermal neutron calibration method using an intense neutron beam from JRR-3M

We have developed a thermal neutron calibration method using a reactor produced neutron beam in JRR-3M of the Japan Atomic Energy Agency. Neutron-induced prompt gamma ray analysis has usually been performed in this beam line. Neutron energy distributions with negligible contributions from epithermal neutrons were measured by a time-of-flight method with a chopper made of ⁶LiF powder. The thermal neutron flux was determined by a gold foil activation method. We found that the thermal neutron beam in JRR-3M was well suited for calibration, neutron detector development or neutron dosimetry.     

Evidence for diffusion-induced convection in ferrofluids from small-angle neutron scattering

Isothermal convection in ferrofluids has been induced by a gradient in particle concentration antiparallel to a magnetic field gradient. The deviation of local particle concentration from its equilibrium value produced by the convective motion of the whole fluid gives rise to a corresponding spatial variation of magnetization. This variation has been observed by magnetic neutron scattering in good agreement with expectations based on flow measurements with an anemometric method.