Rie Haruki

Subnanosecond time-resolved x-ray measurements using an organic-inorganic perovskite scintillator

We have developed a fast x-ray detector using an organic-inorganic perovskite scintillator of phenethylamine lead bromide (PhE-PbBr4). The scintillator had a dominant light emission with a fast decay time of 9.9 ns. An x-ray detector equipped with a 0.9-mm-thick PhE-PbBr4 crystal was used to detect nuclear resonant scattering in N61i (the first excited level: 67.41 keV; lifetime: 7.6 ns) by using synchrotron radiation. With this detector, we could successfully record the decaying gamma rays emitted from N61i with a time resolution of 0.7 ns (full width at half maximum) and a relatively high detection efficiency of 24%.

Observation of Barnett fields in solids by nuclear magnetic resonance

A magnetic field is predicted to emerge on a particle in a rotating material body even if the body is electrically neutral. This emergent field is called a Barnett field. We show that nuclear magnetic resonance (NMR) enables direct measurement of the Barnett field in solids. We rotated both a sample and an NMR coil synchronously at high speed and found an NMR shift whose sign reflects that of the nuclear magnetic moments. This result provides direct evidence of the Barnett field. The use of NMR for Barnett field measurement enables the unknown signs of nuclear magnetic moments in solids to be determined.

X-ray detection capability of a BaCl2 single crystal scintillator

The x-ray detection capability of a scintillation detector equipped with a BaCl2 single crystal was evaluated. The scintillation decay kinetics can be expressed by a sum of two exponential decay components. The fast and slow components have lifetimes of 1.5 and 85 ns, respectively. The total light output is 5% that of YAP:Ce. A subnanosecond timing resolution was obtained. The detection efficiency of a 67.41 keV x-ray is 87% for a detector equipped with a BaCl2 crystal 6-mm thick. Thus, excellent timing resolution and high detection efficiency can be simultaneously achieved. Additionally, luminescence decay characteristics under vacuum ultraviolet excitation have been investigated. Radiative decay of self-trapped excitons is thought to be responsible for the fast scintillation component.

Light-induced unfolding and refolding of supramolecular polymer nanofibres

Unlike classical covalent polymers, one-dimensionally (1D) elongated supramolecular polymers (SPs) can be encoded with high degrees of internal order by the cooperative aggregation of molecular subunits, which endows these SPs with extraordinary properties and functions. However, this internal order has not yet been exploited to generate and dynamically control well-defined higher-order (secondary) conformations of the SP backbone, which may induce functionality that is comparable to protein folding/unfolding. Herein, we report light-induced conformational changes of SPs based on the 1D exotic stacking of hydrogen-bonded azobenzene hexamers. The stacking causes a unique internal order that leads to spontaneous curvature, which allows accessing conformations that range from randomly folded to helically folded coils. The reversible photoisomerization of the azobenzene moiety destroys or recovers the curvature of the main chain, which demonstrates external control over the SP conformation that may ultimately lead to biological functions.

High-energy X-ray detection by hafnium-doped organic-inorganic hybrid scintillators prepared by sol-gel method

With the aim of enhancing the efficiency with which plastic scintillators detect high-energy X-rays, hafnium-doped organic-inorganic hybrid scintillators were fabricated via a sol-gel method. Transmission electron microscopy of sampled material reveals the presence of HfxSi1−xO2 nanoparticles, dispersed in a polymer matrix that constitutes the active material of the X-ray detector. With HfxSi1−xO2 nanoparticles incorporated in the polymer matrix, the absorption edge and the luminescence wavelength is shifted, which we attribute to Mie scattering. The detection efficiency for 67.4-keV X-rays in a 0.6-mm-thick piece of this material is two times better than the same thickness of a commercial plastic scintillator-NE142.

Spin pumping efficiency from half metallic Co2MnSi

We present spin pumping using a Heusler alloy Co2MnSi/Pt bilayer film. A spin current is produced by a ferromagnetic resonance (FMR) technique. The pure spin current injected into the Pt layer from the Co2MnSi layer is detected by the inverse spin-Hall effect (ISHE), which converts the spin current into an electric current. We estimated a damping constant of the Co2MnSi/Pt bilayer film from an angular dependence of FMR spectra. Using the damping constant efficiency of spin pumping from the Co2MnSi layer is evaluated. We found that a mixing conductance at the Co2MnSi/Pt interface is comparable to that at a permalloy/Pt interface.

Redox-Dependent Transformation of a Hydrazinobuckybowl between Curved and Planar Geometries

A red-fluorescent heterobuckybowl with an embedded hydrazine structure was synthesized from a cyclobiphenothiazine derivative via a strained cyclobicarbazole. The hydrazinobuckybowl was found to possess bowl and twist structures in the neutral state, a shallow bowl structure in the monocation state, and a planar structure in the dication state by means of X-ray crystallographic analysis, DFT calculations, and a comparison of experimental and calculated (13) C NMR chemical shifts. The hydrazinobuckybowl is the first buckybowl that changes its geometry between curved bowl/twist structures and a planar structure depending on the oxidation state. The drastic geometrical change was possible as a result of the presence of two heteroatoms in the bowl skeleton and the multiple reversible redox reactions of the compound. Owing to the two kinds of bowl and twist conformations, the bowl-inversion dynamics of the hydrazinobuckybowl were found to follow a triple-well potential model.

Nuclear Resonant Quasielastic Scattering from Fe Cations in Nafion Membranes: Effect of Dynamics in a Short Time Range

The effect of the diffusive motion in a short time range on the nuclear resonant quasielastic scattering spectrum is presented. The solution of the Langevin equation, which describes the motion of ...

Dynamics of Fe Cations in Nafion Membranes Studied by Nuclear Resonant Quasielastic Scattering of Synchrotron Radiation

Nuclear resonant quasielastic scattering from ferrous cations in ion-exchange Nafion membranes was measured at room temperature, and the intrinsic dynamics of the cations inside the spherical regio...

X-ray detection capability of a Cs2ZnCl4 single-crystal scintillator

The X-ray detection capability of a scintillation detector equipped with a Cs2ZnCl4 single crystal was evaluated. The scintillation decay kinetics can be expressed as the sum of two exponential decay components. The fast decay component had a decay time constant of 1.8 ns, and its relative intensity was 95%. The total light output was 630 photons/MeV, and a subnanosecond timing resolution of 0.66 ns was obtained. The detection efficiency of 67.4 keV X-rays was 80% for a detector equipped with a 2.2-mm-thick Cs2ZnCl4 crystal. Thus, excellent timing resolution and high detection efficiency were achieved simultaneously.