Diffraction limit of the theory of multiple small-angle neutron scattering by a dense system of scatterers

Multiple small-angle neutron scattering by a high-density system of inhomogeneities has been considered. A combined approach to the analysis of multiple small-angle neutron scattering has been proposed on the basis of the synthesis of the Zernike–Prince and Moliére formulas. This approach has been compared to the existing multiple small-angle neutron scattering theory based on the eikonal approximation. This comparison has shown that the results in the diffraction limit coincide, whereas differences exist in the refraction limit because the latter theory includes correlations between successive scattering events. It has been shown analytically that the existence of correlations in the spatial position of scatterers results in an increase in the number of unscattered neutrons. Thus, the narrowing of spectra of multiple small-angle neutron scattering observed experimentally and in numerical simulation has been explained.     

Research on glass cells for He neutron spin filters

Glass cells play an important role in polarized ³He neutron spin filters. To evaluate the scattering and absorption contribution from glass cells during neutron scattering experiments, we measured small-angle scattering and neutron transmission in GE180 and other glasses. The small-angle neutron scattering measurements revealed that the glasses used for ³He spin filters have acceptably lower scattering: dΣ(Q)/dΩ=4-7×10⁻⁴ cm⁻¹ at Q=0.03-0.12 Å⁻¹. The transmission measurement was performed at J-PARC. Neutron transmission of about 92% through empty GE180 cells was observed over a wide wavelength range 0.014-7.0 Å. To pursue the possibility of being a structural influence on ³He spin relaxation in GE180 glass cells, we performed precise X-ray diffraction measurement using synchrotron radiation at SPring-8. From these measurements, a structural difference was observed among GE180 glasses with different thermal treatments.     

Mesoscopic magnetic inhomogeneities in the low-temperature phase and structure of Sm1−x SrxMnO3 (x < 0.5) perovskite

Results are presented of studies of the ¹⁵⁴Sm_1?x Sr_xMnO₃ system using neutron powder diffraction and small-angle polarized neutron scattering. An analysis of the neutron diffraction spectra showed that at T < 180 K these exhibit typical Jahn-Teller distortions of the manganese-oxygen octahedrons which persist under further cooling and on transition of the sample to a metallic magnetically ordered state. The magnetic contribution to the diffraction is satisfactorily described using the (A _x (A _y )F _z ) model and is interpreted as the coexistence of ferromagnetic and antiferromagnetic phases. The exaggerated widths of the diffraction lines indicate an appreciable contribution from microdeformations evidently associated with the inhomogeneity of the system. Small-angle polarized neutron scattering showed that the Sm system for x = 0.4 and 0.25 is magnetically inhomogeneous in the low-temperature phase. Ferromagnetic correlations occur on scales of around 200 Å and having dimensions greater than 1000 Å which, combined with the temperature hysteresis of the magnetic small-angle scattering intensity observed for an x = 0.4 sample in the low-temperature phase, suggests that the transition is of a percolation nature.     

A new type of compact large-capacity press for neutron and x-ray scattering

We present a new type of compact hydraulic press of 200?t capacity and 60?kg mass provided with two large openings of 140° (equatorial) x 60° (azimuthal) around the sample area. This device has been designed and optimized using finite element calculations, and was built and recently successfully tested. A smaller version with 50 tonnes capacity and 8?kg mass is also available. This ‘VX’ type Paris–Edinburgh press is expected to have numerous applications in neutron and X-ray scattering whenever large sample volumes (typically 1–100?mm³) are required, in particular for angle-dispersive powder neutron diffraction on reactor sources, single crystal neutron diffraction, and inelastic neutron and X-ray scattering.     

米氏理论的近似及在粒度测量中的应用

将夫琅禾费衍射理论与几何散射 (包括折射和反射 )相结合 ,给出平行光入射下圆形颗粒在前向大角度范围内的散射光强分布近似算法。由于考虑了衍射、折射和反射相互间的干涉效应和颗粒对光的吸收性 ,对于正常或非正常衍射状态下无因次参量α≥ 40的耗散颗粒 ,在前向 0°～ 60°散射之内 ,该方法对散射光强计算结果与米氏理论结果是吻合的。由于计算速度比米氏理论快 ,有效角度范围比夫琅禾费衍射理论宽 ,因而适合于大颗粒的前向光强计算。将这一计算方法应用到大角度采光时的激光粒度测量实验中 ,收到了良好的效果     

Investigation of multiple ultrasmall-angle neutron scattering with the aid of a double-crystal diffractometer

A method of multiple small-angle neutron scattering (MSANS), used to obtain information about inhomogeneities of substances, is considered. Experimental schemes and theory of a double-crystal diffractometer intended for measuring multiple small-angle neutron scattering are described. Methods used to approximate MSANS angular distributions at a low concentration of inhomogeneities and based on Moliére’s theory are reviewed. Their applicability is demonstrated for the examples ofMSANS spectra of samples from ferromagnetic iron-nickel alloys, aluminum powders, and high-T _c superconductor ceramic materials. Theoretical and experimental investigations of interference effects that manifest themselves in multiple small-angle neutron scattering on systems containing high concentrations of scatterers are reported.     

Atomic and superatomic structures of solid solutions of zirconium and calcium oxides

Solid solutions of the ZrO₂-CaO system with 7, 9.6, and 20 mol % of calcium oxide are analyzed by X-ray and neutron diffraction and small-angle neutron scattering. Samples are synthesized by the sol-gel method and annealed at the temperature T = 600°C for 4 h. All samples have a tetragonal structure (P4₂/nmc space group). The size of crystallites is 10–20 nm. Small-angle neutron scattering curves are characterized by a peak near the momentum transfer q = 0.5 nm⁻¹. The existence of the peak is caused by correlation between solid nanoparticles in the samples. Density correlation functions are numerically computed from the experimental small-angle scattering cross-sections by the inverse Fourier transform. Correlation lengths, concentrations of scattering nanoparticles, and specific surface areas of the samples are determined.     

Long-wavelength magnetic excitations in the Zn0.55Mn0.45Fe2O4 ferrite

The small-angle neutron scattering energy spectra of the Zn_0.55Mn_0.45Fe₂O₄ ferrite are analyzed at different temperatures (both below and above T _C ? 390 K) and scattering angles. The thermal expansion coefficient α(T) is measured in the temperature range 80–600 K. It is revealed that inelastic neutron scattering is governed not only by spin waves of the Holstein-Primakoff type but also by the substantial contribution of additional long-wavelength magnetic excitations. The physical nature of these low-energy magnetic excitations is discussed.     

Specific features of neutron scattering upon heat treatment of the Co67Fe31V2 alloy

This paper reports on the results obtained from small-angle neutron scattering investigations during annealing of two plates of the Co₆₇Fe₃₁V₂ alloy under heating the first and second samples to 360 and 500°C, respectively, as well as in applied weak magnetic fields (H ≈ 3 Oe). To elucidate the role of the vanadium impurity, measurements have also been performed on the Co₆₈F₃₂ alloy. It has been revealed using neutron diffraction that, at temperatures below 360°C, the Fe and Co atoms begin to undergo ordering in the samples, which results in a change in the space group of the crystal structure. With an increase in the temperature, a fine-dispersed phase is formed in the Co₆₇Fe₃₁V₂ alloy, which leads to a qualitative change in the small-angle neutron scattering pattern. It has been found that, after annealing and magnetization (H > 4 kOe) of the second sample, there is a strong difference in the integrated intensities of scattered neutrons for opposite directions of their spins in the primary beam.     

A Gorizont neutron reflectometer—small-angle spectrometer based on the IN-06 pulsed neutron source

The Gorizont time-of-flight neutron reflectometer—small-angle spectrometer has been designed, manufactured, and assembled to operate with the IN-0 6 pulsed neutron source. The instrument has a vertical neutron scattering plane enabling research on liquid surfaces and interfaces. Model calculations of neutron spectra, beam profiles, and spectrometer resolutions have been performed via the Monte Carlo method. The spectrometer operates at wavelengths from 1.5 to 9 Å and ensures measurements in the momentum-transfer range of 0.003—1.5 Å^-1.     

Two-dimensional spatially ordered system of nickel nanowires probed by polarized SANS

Structural and magnetic properties of two-dimensional spatially ordered system of ferromagnetic nickel nanowires embedded into Al₂O₃ matrix have been studied using polarized small-angle neutron scattering. The small-angle diffraction pattern exhibits many diffraction peaks, which corresponds to the scattering from highly correlated hexagonal structure of pores and magnetic nanowires. Magnetic contribution to the scattering has complex behavior and cannot be explained without taking into account stray fields located between magnetized nanowires.     

Small-angle magnetic scattering from a dilute amorphous Fe(Tb) alloy

Low temperature neutron scattering measurements on an amorphous alloy of composition Tb_0.018 Fe_0.982 reveal anomalous small-angle magnetic scattering similar to that observed in the more rare-earth-rich compounds TbFe₂ and HoFe₂. Inferences are drawn from the angular dependence of the scattering concerning cluster size and magnetic structure.     

Oxidation and magnetic states of chalcopyrite CuFeS2: A first principles calculation

The ground state band structure, magnetic moments, charges and population numbers of electronic shells of Cu and Fe atoms have been calculated for chalcopyrite CuFeS₂ using density functional theory. The comparison between our calculation results and experimental data (X-ray photoemission, X-ray absorption and neutron diffraction spectroscopy) has been made. Our calculations predict a formal oxidation state for chalcopyrite as Cu¹⁺Fe³⁺S ₂ ^2? . However, the assignment of formal valence state to transition metal atoms appears to be oversimplified. It is anticipated that the valence state can be confirmed experimentally by nuclear magnetic and nuclear quadrupole resonance and Mössbauer spectroscopy methods.     

A second-order vibrational model applied to the scattering of electrons and α-particles from 12C

Transition densities for monopole excitations and for virtual excitations are derived in the second-order vibrational model. Form factors for electron scattering calculated in the Born approximation and angular distributions for α-particle scattering, obtained in coupled channel calculations, are compared with experimental results for the elastic scattering and the inelastic scattering from the 2⁺ level at 4.44 MeV, the 0⁺ level at 7.65 MeV and the 3^? level at 9.64 MeV in ¹²C.     

Effect of neutron irradiation on the long-wavelength magnetic excitations in the Zn0.60Ni0.40Fe2O4 ferrite

An energy analysis of small-angle neutron scattering in the Zn_0.60Ni_0.40Fe₂O₄ ferrite nonirradiated and irradiated by fast neutrons has been performed. It has been revealed that the inelastic neutron scattering in the initial ferrite below T _C is due to not only the intradomain spin waves but also the significant contribution of the intraboundary long-wavelength magnetic excitations (w) and those localized near the domain boundaries (nw). The number of these magnetic excitations in the irradiated sample is significantly smaller. The elevated density of states of the w and nw magnetic excitations is assumed to be related to the competition between the intersublattice and intrasublattice exchange interactions, which is significantly weakened in the irradiated ferrite, where the corresponding exchange integrals are related by the inequality J _AB ? J _BB .     

Elastic neutron scattering measurements on239Pu in the energy range between 0.19 and 0.38 MeV

Five neutron scattering angular distributions of²³⁹Pu were measured in the primary neutron energy range between 0.19 and 0.38 MeV. The absolute cross section results are presented in the form of coefficients of Legendre polynomial expansions. Integrated scattering cross sections are also given. Cross section calculations using a central optical model were made and their results were compared with the experimental values.     

Counterion condensation in ionic micelles as studied by a combined use of SANS and SAXS

We report a combined use of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) to the study of counterion condensation in ionic micelles. Small-angle neutron and X-ray scattering measurements have been carried out on two surfactants cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium chloride (CTACl), which are similar but having different counterions. SANS measurements show that CTABr surfactant forms much larger micelles than CTACl. This is explained in terms of higher condensation of Br⁻ counterions than Cl⁻ counterions. SAXS data on these systems suggest that the Br⁻ counterions are condensed around the micelles over smaller thickness than those of Cl⁻ counterions.     

Simulation of Neutron Reflection from the Surface of a Nanostructured Object in the Modified Kinematic Approximation

The applicability of the modified kinematic approximation for simulation of the specular reflection and the diffraction of a neutron beam from regularly ordered nanostructured objects on the surface and in the surface material layer is analyzed. The obtained results are compared with those of the real experiment and simulation of the distorted-wave Born approximation (DWBA). The influence of various factors on the obtained results is analyzed. These factors include the effect of neutron-wave refraction at the interfaces between media, the spectrometer-resolution function, and renormalization of the results for a nonspecular scattering signal based on data obtained for a specular channel. It is shown that, in many cases, it is possible to obtain rather good agreement with the experimental data and with the results of calculations using DWBA methods and of calculations using the Parratt algorithm.     

Small angle diffuse neutron scattering: Measurements on V2O3 in the temperature range 400–600 K

Cold neutron small-angle scattering measurements on pure V₂O₃ in the high-temperature transition domain shows an anomalous feature namely a peak and a bump in the range 500–570 K. It is suggested that a plausible origin of this anomaly is the formation of giant “correlation” clusters of size ～ 600 Å and a magnetic moment density ～ 10^-7 μ/ų as the system suffers a broad M-I transition.     

Magnetic structure and magnetic properties of non-stoichiometric Fe1−xO

The magnetic structure of non-stoichiometric Fe_1?xO was investigated by neutron scattering measurements on a quenched single crystal of Fe_0.91O below the Néel temperature. In each defect cluster, there exist ferromagnetic moments and they are arranged antiferromagnetically with the periodicity of twice that of the atomic superstructure. Relation between the defect structure and the magnetic properties for a wide range of compositions was discussed.