Tuning Neutron Resonance Spin-Echo Spectrometers with Pulsed Beams

The neutron spin-echo spectroscopy technique involving pulsed beams can be used to effectively access a wide range of space-time correlations of condensed matter. In this study, the features of this technique, in particular, the modulation of the intensity with zero effort (MIEZE) by using pulsed beams, which is based on the quantum-state manipulation of the neutron spin and energy, are comprehensively examined. A formulation of the MIEZE combined with the time of flight method (TOF MIEZE) is established by considering the characteristics of the pulsed neutron beams. Moreover, a parameter, namely, the detuning parameter, is introduced as a measure of the magnitude of detuning from the optimized instrumental state, known as the spin-echo condition. The phase and frequency shifts of the neutron intensity signals resulting from the TOF MIEZE under various configurations are investigated systematically. It is found that the detuning parameter equals the derivative of phase with respect to the TOF, whose zero-point corresponds to the spin-echo condition. The theoretical predictions on phase and frequency shifts by the established formulation are well validated by the experiments using an intense pulsed neutron source. The detuning parameter helps clarify the principle of the TOF MIEZE technique and can provide practical guidance regarding the implementation and optimization of spectrometers

Neutron detection in the frame of spatial magnetic spin resonance

AbstractThis work is related to neutron detection in the context of the polarised neutron optics technique of spatial magnetic spin resonance. By this technique neutron beams may be tailored in their spectral distribution and temporal structure. We have performed experiments with very cold neutrons (VCN) at the high-flux research reactor of the Institut Laue Langevin (ILL) in Grenoble to demonstrate the potential of this method. A combination of spatially and temporally resolving neutron detection allowed us to characterize a prototype neutron resonator. With this detector we were able to record neutron time-of-flight spectra, assess and minimise neutron background and provide for normalisation of the spectra owing to variations in reactor power and ambient conditions at the same time

重金属汚染地域の金属耐性コケ植物, タチゴケ, ホンモンジゴケ及びキヘチマゴケにおける銅, 鉛及び亜鉛のキャラクタリゼーション

[論文] Articl

Direct observations of spin fluctuations in spin-hedgehog-anti-hedgehog lattice states in MnSi1−x_{1-x}Gex_x (x=0.6x=0.6 and 0.80.8) at zero magnetic field

The helimagnetic compounds MnSi$_{1-x}$Ge$_{x}$ show the three-dimensional multiple-$q$ order as referred to as spin-hedgehog-anti-hedgehog (SHAH) lattice. Two representative forms of SHAH are cubic-3$q$ lattice with $q \| \langle100\rangle$ and tetrahedral-4$q$ lattice with $q \| \langle111\rangle$, which show up typically for $x=1.0-~0.8$ and for $x=0.6$, respectively. Here, we have investigated the spin fluctuations in the MnSi$_{1-x}$Ge$_{x}$ polycrystalline samples with $x=0.6$ and $0.8$ by using the time-of-flight (TOF) neutron inelastic scattering and MIEZE-type neutron spin echo techniques to elucidate the microscopic origin of the unconventional Hall effect in the SHAH lattice states. This research is motivated by the observation of a sign change in the unconventional Hall resistivity as a function of temperature [Y. Fujishiro et al., Nat. Comm. $\textbf{10}$, 1059 (2019)]. The present results reveal the correspondences between the temperature ranges where the positive Hall resistivity and spin fluctuations are observed. These results agree well with the theoretical model of the conduction electrons scattered by the fluctuating spin clusters with a non-zero average of sign-biased scalar spin chirality as a mechanism of the positive Hall resistivity [H. Ishizuka and N. Nagaosa, Sci. Adv. $\textbf{4}$, eaap9962 (2018)].Comment: 10 pages, 8 figure

MONOPOL - A traveling-wave magnetic neutron spin resonator for tailoring polarized neutron beams

We report on first experimental tests of a neutron magnetic spin resonator at a very cold neutron beam port of the high flux reactor at the ILL Grenoble. When placed between two supermirror neutron polarizers and operated in a pulsed traveling-wave mode it allows to decouple its time- and wavelength-resolution and can therefore be used simultaneously as electronically tunable monochromator and fast beam chopper. As a first ‘real’ scientific application we intend its implementation in the PERC (p roton and e lectron r adiation c hannel) project related to high-precision experiments in neutron beta decay

Time-resolved serial femtosecond crystallography reveals early structural changes in channelrhodopsin

X線自由電子レーザーを用いて、光照射によるチャネルロドプシンの構造変化の過程を捉えることに成功. 京都大学プレスリリース. 2021-03-26.Channelrhodopsins (ChRs) are microbial light-gated ion channels utilized in optogenetics to control neural activity with light . Light absorption causes retinal chromophore isomerization and subsequent protein conformational changes visualized as optically distinguished intermediates, coupled with channel opening and closing. However, the detailed molecular events underlying channel gating remain unknown. We performed time-resolved serial femtosecond crystallographic analyses of ChR by using an X-ray free electron laser, which revealed conformational changes following photoactivation. The isomerized retinal adopts a twisted conformation and shifts toward the putative internal proton donor residues, consequently inducing an outward shift of TM3, as well as a local deformation in TM7. These early conformational changes in the pore-forming helices should be the triggers that lead to opening of the ion conducting pore

Overscreening Induced by Ionic Adsorption at the Ionic Liquid/Electrode Interface Detected Using Neutron Reflectometry with a Rational Material Design

Neutron reflectometry (NR) has been utilized to study the electric double layer (EDL) of ionic liquids (ILs), however, further improvement of the sensitivity toward interfacial structure would be desirable. We recently proposed two ways to improve the NR sensitivity toward the EDL structure at the IL/electrode interface (J. Phys. Chem. C, 123 (2019) 9223). First, as the electrode, a thin film of metal (Nb) was used with the scattering length density (SLD) and thickness controlled to sensitively analyze the potential dependent EDL structure. Second, the IL cation and anion were chosen so that they have large size and large SLD difference, both of which also increase the sensitivity. In the present study, we have further explored this rational material design for the sensitivity enhancement, by changing the film metal from Nb to Bi whose SLD is closer to those for two bulk materials: Si and the IL used, trihexyltetradecylphosphonium bis(nonafluorobutanesulfonyl)amide. We successfully observed not only the first ionic layer in the EDL but also the overlayers, revealing that the IL cation is specifically adsorbed on the electrode and that the cation-rich first layer induces overscreening in the overlayers up to the third ionic layer

Phase correction method in a wide detector plane for MIEZE spectroscopy with pulsed neutron beams

In this study, we propose a phase correction method for a type of neutron spin echo spectroscopy, known as modulation of intensity with zero effort using a time-of-flight method (TOF-MIEZE). The phase of the MIEZE signal sensitively varies with the neutron flight path lengths. The geometrical lengths from the sample position to the flat detector plane differ depending on the positions on the detector plane. Integrating the phase-shifted signals may decrease the signal contrast solely through the geometrical path-length deviations. To measure the decrement of contrast accurately, which corresponds to the intermediate scattering function, the position-dependent phase shifts must be corrected. The data correction is performed by shifting the MIEZE signal in time depending on path-length deviations, the MIEZE frequency, and neutron wavelengths. In the calculation of path-length deviations, the sample is assumed to be a point scatterer while a detector inclination is taken into account. We also discuss the relation between the frequency shift of TOF-MIEZE signal and path-length deviation, which is helpful to quantify phase shifts larger than 2π. The presented phase correction method is demonstrated with a 32 × 32 cm² area detector for a 200 kHz TOF-MIEZE signal scattered from an elastic sample