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Abstract  

The ultra-slow modes with a relaxation time much longer than 1 ns are discovered by a time-resolved spectroscopy in uniaxial ferroelectric (NH2CH2COOH)3H2SO4 (TGS) and in glass-former HOCH2(CHOH)4CH2OH (D-sorbitol). A mode discovered in TGS is a thermal relaxational mode and is proved to be the physical origin of the central peak found by Brillouin scattering. Two modes are discovered in D-sorbitol. One is a thermal relaxational mode. The other is a mode characterized by the Kohlraush-Williams-Watts function with a relaxation time R. A remarkable result is that R indicates a critical behavior not at the liquid-glass transition temperature T g =–7°C but at the ergodic to nonergodic transition temperature T c=33°C.

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Journal of Thermal Analysis and Calorimetry
Authors: K. Fujii, Y. Matsumoto, Y. Kaieda, D. Kobayashi, Y. Umebayashi, and S. Ishiguro

Abstract  

Cobalt(II) chloro complexation has been studied by titration calorimetry and spectrophotometry in solvent mixtures of N-methylformamide (NMF) and N,N-dimethylformamide (DMF). It revealed that a series of mononuclear CoClnn (2–n)+ (n=1–4) complexes are formed in the mixtures of NMF mole fraction x NMF=0.05 and 0.25, and the CoCl+, CoCl3 and CoCl4 2– complexes in the mixture of x NMF=0.5, and their formation constants, enthalpies and entropies were obtained. As compared with DMF, the complexation is markedly suppressed in the mixtures, as well as in NMF. The decreasing formation constant of CoCl+ with the NMF content is mainly ascribed to the decreasing formation entropy. DMF is aprotic and thus less-structured, whereas NMF is protic to form hydrogen- bonded clusters. In DMF-NMF mixtures, solvent clusters in neat NMF are ruptured to yield new clusters involving DMF, the structure of which depends on the solvent composition. The entropy of formation of CoCl+ will be discussed in relation to the liquid structure of DMF, NMF and their mixtures.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: F. Ambe, Y. Ohkubo, S. Ambe, Y. Kobayashi, T. Okada, Y. Yanagida, J. Nakamura, K. Asai, Y. Kawase, and S. Uehara

Abstract  

The features of time-differential perturbed angular correlation (TDPAC) in studies on local chemical structures around impurity atoms are described in comparison with those of Mössbauer emission spectroscopy with four typical examples of recent applications to metal oxide systems, namely,99Rh 99Ru in -Fe2O3 and YBa2Cu3O7– and117Cd 117In in MO (M=Mn, Co, Ni) and BaRu2/3Cd1/3O3.

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Abstract  

A new picosecond pulse radiolysis Twin LINAC System has been constructed recently at Nuclear Engineering Research Laboratory at the University of Tokyo. The time resolution of the system is 20 ps and the system has a versatile capability for pulse radiolysis study. The outline of the facility is introduced. Some research carried out using the facility is presented. The examples are radiolysis of CCl4 and n-C21H44.

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Abstract  

Transport and distribution of metal ions in rice and soybean plants were studied using multitracers produced by irradiating an Au target by 135 MeV/nucleon12C,14N, or16O ions accelerated by RIKEN Ring Cyclotron. The multitracer consisted of radioisotopes of the following elements: Be, Na, Sc, Mn, Fe, Co, Zn, Se, Rb, Sr, Y, Zr, Nb, Ag, Te, Ba, Ce, Pm, Eu, Gd, Tb, Tm, Yb, Lu, Hf, Ir, and Pt. Rice and soybean plants were grown in a nutrient solution and also on soil containing a multitracer. -ray spectroscopy of different parts of the plants showed that all the elements were more or less taken up by roots, while appreciable transport to leaves and seeds was observed only for Mn, Zn, Se, Rb, Sr, and Ba.

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Abstract  

Resonant nuclear inelastic scattering (NIS) spectra of (Sr,Ca)(Fe,Co)O3- d and (Ba,Ca)(Fe,Co)O3- d were measured with the energy resolution of 3.5 MeV by detecting the 6.3 keV Fe Ka X-rays following after Mössbauer effect on 57Fe transition excited by the monochromatized 14.41 keV synchrotron radiation. Both series of oxides annealed in air and in CO2 were examined. Soft phonon peak arising at ~8 MeV in NIS spectra of (Sr0.5Ca0.5)(Fe0.5Co0.5)O3- d and (Ba0.5Ca0.5)FeO3- d was found to be correlated with the oxygen ordering into brownmillerite structure, whereas more complex multi-phonon structure was observed in the spectra of less oxygen-deficient oxides such as (Sr0.95Ca0.05)(Fe0.5Co0.5)O3- d and (Sr0.7Ca0.3)(Fe0.5Co0.5)O3- d showing rather random distrubution of the oxygen vacancies. The changes in phonon DOS after CO2 absorbtion were also detected. Lam-Mössbauer factors of these oxides were calculated on the base of Debye Model.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: X. Zhao, Y. Itoh, Y. Aoyagi, T. Sugano, K. Hirata, Y. Kobayashi, T. Ohdaira, R. Suzuki, and T. Mikado

Abstract  

Positron and positronium annihilation investigations were applied to nanocrystalline silicon (nc-Si) thin films, for the first time. The nc-Si thin films with average grain diameters of 3–5 nm show intense blue luminescence at room temperature. The nanometer-sized Si crystallites formed in amorphous Si (a-Si) matrix give rise to this luminescence. Very highS-parameters up to 0.62 were observed in the as-grown a-Si thin film suggesting positronium formation in the a-Si layer. The average lifetime of the positrons in the a-Si was determined to be about 520 ps. TheS-parameters dropped significantly to 0.53 by crystallization of the thin film at 800 °C for 10 seconds, which was almost the same to the value observed in bulk Si (100) substrate. Further crystallization from 60 seconds to 1 hour showed smaller change in theS-parameters than that from the a-Si to 10 seconds. The large change in theS-parameters due to the annealing might be caused by the formation of Si nanocrystallites in a-Si matrix suggesting that positron is a sensitive probe for structural investigations of the nc-Si materials.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Y. Kobayashi, Y. Tsuruoka, M. Kubo, H. Nonaka, Y. Yamada, Y. Sakai, H. Shoji, W. Sato, A. Shinohara, Y. Watanabe, and H. Matsue

Abstract  

In order to investigate the physical and chemical effects of neutron capture reaction, a neutron in-beam Mössbauer spectroscopic study on two isomorphs of iron disulfide: pyrite and marcasite, were carried out with a parallel plate avalanche counter at room temperature. In both compounds only two major products accounted for the obtained spectrum: one with Mössbauer parameters close to the parent compound and the other one considered to be a new product. The yield of the parent-like species was different in the two isomorphs.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Ch. He, E. Hamada, T. Suzuki, H. Kobayashi, K. Kondo, V. Shantarovich, and Y. Ito

Abstract  

A new pulsed mono-energetic slow positron beam as well as the conventional positron annihilation lifetime spectroscopy (PALS) have been applied to study the sub-surface and the bulk of epoxy polymer. Significant changes of o-Ps parameters were found at a short distance from the surface. The lifetime of o-Ps was observed to decrease with increasing the positron implantation depth, while its intensity increased. The temperature effect on o-Ps parameters at sub-surface was also investigated. The glass transition temperature for the sub-surface was lower than that for the bulk. Furthermore, the thermal expansion coefficient of the sub-surface was found smaller than that of the bulk.

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