The protocol of refinement in neutron protein crystallographic analysis is described in this article. During the refinement, there are several features specialized for neutron experiment:(1) the mixed chemical structure of deuterium and hydrogen atoms, (2) solvent molecules around the protein, and the deuterium exchange in the polypeptide chain. We demonstrate the example of neutron refinement steps, using rubredoxin mutant, of which neutron diffraction collected using BIX-3 diffractometer at JRR-3 in Japan Atomic Energy Agency. The X-ray refinement program of CNS was used for the present refinement. Scattering lengths, stereochemical parameters, and command input files were modified for neutron experiment. These files would be the templates for the neutron protein crystallographic analysis.
Proton conductivity of Nafion® membrane is varied by humidity and it has been thought to be affected by the cluster structure of the membrane. We applied Small-Angle Scattering technique under humidity-controlled atmosphere with X-ray (SAXS) and neutron (SANS) to clarify the relationship between the cluster structure and molecular structure in two types of Nafion® membrane, N115 and NE151F, which have different equivalent weight (EW). The proton conductivity of N115 is higher than that of NE151F. By these two measurements, three different sized periodic structures were observed in the Nafion® membrane. Contrast variation method (D/H=60/40, 75/25, 80/20, 90/10) was also applied in SANS experiments and it was suggested that two of three peaks are originated from two different sizes of water clusters. A distinguishing peak at q=0.2 [Å-1], which shifts to lower q region by humidity increase, was reproduced by a simulation of Dissipative Particle Dynamics (DPD): the shifts of the peak was interpreted as the swelling of cluster structure. The size of the cluster calculated from the peak position is positively correlated with the proton conductivity. Finally, The effect of EW on the proton conductivity of Nafion® membrane was briefly discussed from the point of its cluster structure.
Neutron diffraction has been employed for stress evaluation of various mechanical components. The hkl lattice plane spacings in a diffraction gauge volume are measured, then elastic strains are calculated and finally stresses are determined by using the Hooke's law. Since the real engineering mechanical parts are so complfcated that more sophisticated method must be progressed to obtain stress distribution in the inside of a sample. Current advances on this issue are reviewed.
Neutron scattering experiments have been performed to study spin excitations in the overdoped La2-xSrxCuO4 (0.25≤x≤0.30) using triple-axis and time-of-flight techniques. Low energy magnetic excitations (ω<10 meV) show incommensurate peaks for the superconducting samples with a maximum at-6 meV in the energy spectrum. As doping increases, the maximum of the dynamic susceptibility X″(ω) decreases linearly with Tc and, finally, the low energy excitations become unobservable at x=0.30 coincidentally with the disappearance of bulk superconductivity. Magnetic excitation spectra in the intermediate energy range (20<ω<100meV) are found to decrease monotonically with doping. These observations are discussed in terms of a phase separation of the system into a remnant magnetic region, which possibly consists of a stripe structure and supports the superconductivity, and a non-magnetic metallic region.
A spin-polarized neutron diffraction study was carried out in a multiferroic (antiferromagnetic ferroelectric) TbMnO3. A large flipping ratio of magnetic diffraction intensity shows that helical configuration of spin ordering appears in the low-temperature ferroelectric antiferromagnetic phase, but not in the intermediate-temperature paraelectric antiferromagnetic phase. The sense of the helix is controlled by the direction of the ferroelectric polarization. The inverse Dialoshinskii-Moriya interaction, or so-called spin-current mechanism, can also explain the temperature dependence of the flipping ratio of the scattering intensity.
A spin-polarized neutron diffraction study was carried out in a multiferroic antiferromagnetic An introduction of how to study phonon dynamics by inelastic neutron scattering is provided. The process of deducing interatomic force constants from measured phonon dispersion curves and phonon scattering intensity is explained. Using the technique, an example of analysis on a cage compound is described. A concept of phonon-phonon scattering associated with thermal conductivity is also explained.