Materials and Life Science Experimental Facility at the Japan Proton Accelerator Research Complex III: Neutron Devices and Computational and Sample Environments

New Design of a Sample Cell for Neutron Reflectometry in Liquid–Liquid Systems and Its Application for Studying Structures at Air–Liquid and Liquid–Liquid Interfaces

Knowledge of interfacial structures in liquid–liquid systems is imperative, especially for improving two-phase biological and chemical reactions. Therefore, we developed a new sample cell for neutron reflectometry (NR), which enables us to observe the layer structure around the interface, and investigated the adsorption behavior of a typical surfactant, sodium dodecyl sulfate (SDS), on the toluene-d8-D2O interface under the new experimental conditions. The new cell was characterized by placing the PTFE frame at the bottom to produce a smooth interface and downsized compared to the conventional cell. The obtained NR profiles were readily analyzable and we determined a slight difference in the SDS adsorption layer structure at the interface between the toluene-d8-D2O and air-D2O systems. This could be owing to the difference in the adsorption behavior of the SDS molecules depending on the interfacial conditions.

First Experiment of Spin Contrast Variation Small-Angle Neutron Scattering on the iMATERIA Instrument at J-PARC

Recently, we have developed a novel dynamic nuclear polarization (DNP) apparatus with a magnetic field of 7 T and a sample temperature of 1 K. High proton spin polarizations from −84% to 76%, for TEMPO doped polystyrene samples, have been demonstrated. This DNP apparatus satisfies the simultaneous requirement for quick and easy sample exchange and high DNP performance. On the iMATERIA (BL20) instrument at J-PARC, the first beam experiment using this DNP apparatus has been performed. For this experiment, the beamline was equipped with a supermirror polarizer. The stray magnetic field due to the superconducting magnet for DNP was also evaluated. The stray magnetic field plays an important role for in maintaining the neutron polarization during the transportation from the polarizer to the sample. The small-angle neutron scattering (SANS) profiles of silica-filled rubber under dynamically polarized conditions are presented. By applying our new analytical approach for SANS coherent scattering intensity, neutron polarization (PN) as a function of neutron wavelength was determined. Consequently, for the neutron wavelength, range from 4 Å to 10 Å, |PN| was sufficient for DNP-SANS studies.

Fine-Structure Analysis of Perhydropolysilazane-Derived Nano Layers in Deep-Buried Condition Using Polarized Neutron Reflectometry

A large background scattering originating from the sample matrix is a major obstacle for fine-structure analysis of a nanometric layer buried in a bulk material. As polarization analysis can decrease undesired scattering in a neutron reflectivity (NR) profile, we performed NR experiments with polarization analysis on a polypropylene (PP)/perhydropolysilazane-derived SiO₂ (PDS)/Si substrate sample, having a deep-buried layer of SiO₂ to elucidate the fine structure of the nano-PDS layer. This method offers unique possibilities for increasing the amplitude of the Kiessig fringes in the higher scattering vector (Q_z) region of the NR profiles in the sample by decreasing the undesired background scattering. Fitting and Fourier transform analysis results of the NR data indicated that the synthesized PDS layer remained between the PP plate and Si substrate with a thickness of approximately 109 Å. Furthermore, the scattering length density of the PDS layer, obtained from the background subtracted data appeared to be more accurate than that obtained from the raw data. Although the density of the PDS layer was lower than that of natural SiO₂, the PDS thin layer had adequate mechanical strength to maintain a uniform PDS layer in the depth-direction under the deep-buried condition.

The Large-Area Detector for Small-Angle Neutron Scattering on iMATERIA at J-PARC

An area detector with a central hole structure was built up for small-angle neutron scattering (SANS) on the iMATERIA instrument at Japan Proton Accelerator Research Complex (J-PARC). Linear position-sensitive detector tubes filled with 3He gas were arranged in three layers leaving a central hole. As a result of the calibration process, a SANS measurement with wide q-range from 0.007 Å−1 to 4.3 Å−1 was achieved in double-frame operation, supplying neutrons with wavelengths from 1 Å to 10 Å. As a merit of this central hole structure, neutron transmission can be measured simultaneously to reduce experimental time and effort. This is ideal for time-resolved studies, in which the sample transmission can be time-dependent, throughout the whole experiment. Additionally, the data storage system in ‘event mode’ format provides an excellent platform for such time-resolved experiments.

Kinetics of silver photodiffusion into amorphous S-rich germanium sulphide – neutron and optical reflectivity

Silver photodiffusion is one of the attractive photo-induced changes observed in amorphous chalcogenides. In this research, we focus on amorphous S-rich germanium sulphide and study the kinetics of the silver photodiffusion by neutron reflectivity, as well as optical reflectivity. It was found from the neutron reflectivity profiles with 30 s time resolution that silver dissolved into the germanium sulphide layer, forming a metastable reaction layer between the Ag and the germanium sulphide layers, within 2 min of light exposure. Subsequently, silver slowly diffused from the metastable reaction layer to the germanium sulphide host layer until the Ag concentration in both layers became identical, effectively forming one uniform layer; this took approximately 20 min. Optical reflectivity reveals the electronic band structure of the sample, complementary to neutron reflectivity. It was found from the optical reflectivity measurement that the metastable reaction layer was a metallic product. The product could be Ag8GeS6-like form, which is regarded as the combination of GeS2 and Ag2S, and whose backbone is composed of the GeS4 tetrahedral units and the S atoms. We attribute the first quick diffusion to the capture of Ag ions by the latter S atoms, which is realised by the S–S bond in amorphous S-rich germanium sulphide, while we attribute the second slow diffusion to the formation of the Ag–Ge–S network, in which Ag ions are captured by the former GeS4 tetrahedral units.

High stereographic resolution texture and residual stress evaluation using time-of-flight neutron diffraction

The division of neutron detector panel regions has improved the precision of complex texture evaluation and appropriate sample rotation enhances the texture reliability in a limited neutron beam time. The TAKUMI instrument has achieved satisfactory texture precision for a limestone standard sample. The compressive rolling direction–transverse direction in-plane stress field was quantitatively measured in martensite layers of a martensite–austenite multilayered steel, and this stress field was found to originate from the martensite transformation strain and the linear contraction misfit between austenite layers and newly transformed martensite layers.

Neutron diffraction texture measurements provide bulk averaged textures with excellent grain orientation statistics, even for large-grained materials, owing to the probed volume being of the order of 1 cm³. Furthermore, crystallographic parameters and other valuable microstructure information such as phase fraction, coherent crystallite size, root-mean-square microstrain, macroscopic or intergranular strain and stress, etc. can be derived from neutron diffractograms. A procedure for combined high stereographic resolution texture and residual stress evaluation was established on the pulsed-neutron-source-based engineering materials diffractometer TAKUMI at the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Center, through division of the neutron detector panel regions. Pole figure evaluation of a limestone standard sample with a well known texture suggested that the precision obtained for texture measurement is comparable to that of the established neutron beamlines utilized for texture measurement, such as the HIPPO diffractometer at the Los Alamos Neutron Science Center (New Mexico, USA) and the D20 angle-dispersive neutron diffractometer at the Institut Laue–Langevin (Grenoble, France). A high-strength martensite–austenite multilayered steel was employed for further verification of the reliability of simultaneous Rietveld analysis of multiphase textures and macro stress tensors. By using a texture-weighted geometric mean micromechanical (BulkPathGEO) model, a macro stress tensor analysis with a plane stress assumption showed a rolling direction–transverse direction (RD–TD) in-plane compressive stress (about −330 MPa) in the martensite layers and an RD–TD in-plane tensile stress (about 320 MPa) in the austenite layers. The phase stress partitioning was ascribed mainly to the additive effect of the volume expansion during martensite transformation and the linear contraction misfit between austenite layers and newly transformed martensite layers during the water quenching process.