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Journal Articles

External exposure dose estimation by electron spin resonance technique for wild Japanese macaque captured in Fukushima Prefecture

Oka, Toshitaka; Takahashi, Atsushi*; Koarai, Kazuma; Mitsuyasu, Yusuke*; Kino, Yasushi*; Sekine, Tsutomu*; Shimizu, Yoshinaka*; Chiba, Mirei*; Suzuki, Toshihiko*; Osaka, Ken*; et al.

Radiation Measurements, 134, p.106315_1 - 106315_4, 2020/06

The relationship between the CO$$_{2}$$ radical intensity and the absorbed dose (dose response curve) of tooth enamel of Japanese macaque was observed by electron spin resonance and the detection limit of our system was estimated to be 33.5 mGy, which is comparable to the detection limit for human molar teeth. Using the dose response curve, external exposure dose for seven wild Japanese macaques captured in Fukushima prefecture were examined. The results suggest that the external exposure dose for the wild Japanese macaques were ranged between 45 mGy to 300 mGy.

Journal Articles

Inverse magnetic susceptibility fabrics in pelagic sediment; Implications for magnetofossil abundance and alignment

Usui, Yoichi*; Yamazaki, Toshitsugu*; Oka, Toshitaka; Kumagai Yuho*

Journal of Geophysical Research; Solid Earth, 124(11), p.10672 - 10686, 2019/11

We report the discovery of inverse AMS fabrics from pelagic clay recovered by a $$sim$$12 m long piston core from the western North Pacific. Rock magnetic data and ferromagnetic resonance spectroscopy indicated that magnetofossils account for most of the mean susceptibility regardless of normal or inverse AMS, suggesting that the inverse AMS fabrics due to magnetofossils may be widespread in pelagic clay.

Journal Articles

Localization of DNA damage induced by inner-shell ionization

Yokoya, Akinari; Ukai, Masatoshi*; Oka, Toshitaka*; Kai, Takeshi; Watanabe, Ritsuko; Fujii, Kentaro

Shototsu, 11(2), p.33 - 39, 2014/03

no abstracts in English

Journal Articles

Positronium bubble formation in room temperature ionic liquids

Hirade, Tetsuya; Oka, Toshitaka*

Journal of Physics; Conference Series, 443, p.012060_1 - 012060_4, 2013/06

 Times Cited Count:3 Percentile:18.24

Room temperature ionic liquids (IL) have Negligible vapor pressure and other interesting properties. There are many considerable applications of ionic liquids, because of the environmentally friendly property. The radiation chemistry study for IL is very important for nuclear fuel reprocessing. The solvation of excess electrons is affected by molecular dynamics in sub-nano meter scale. Positronium (bond state of electron and positron) has a negative work function and form a bubble in liquids. The formation time is usually very fast as about 1ps that is difficult to observe by experiment. However we succeeded to observe the delayed bubble formation process in IL by use of the positron annihilation age-momentum correlation (AMOC) measurement. This phenomena could explain the anomalous long lifetime of the singlet positronium intrinsic annihilation lifetime. Probably only the lifetime spectra can give the information of bubble formation time in IL.

Journal Articles

Positron annihilation lifetime of irradiated polyimide

Hirade, Tetsuya; Oka, Toshitaka; Morishita, Norio*; Idesaki, Akira; Shimada, Akihiko

Materials Science Forum, 733, p.151 - 154, 2013/00

 Times Cited Count:7 Percentile:3.56

Polyimide polymers such as Kapton show a very good performance at high radiation environment such as in space or in radiation facilities. Positron annihilation lifetime measurement is a widely used method for materials science, and the lifetime of triplet positronium (electron-positron pair) can give important information of free volume of polymers. However, there is no positronium formation in Kapton and hence this method was no applied for polymer studies. Here, we indicated that free positron annihilation lifetime can give information of change of free volume by showing the temperature dependence of the lifetime. We applied this method to study irradiation effects on Kapton and we successfully indicated that the free positron lifetime can be applied for polymer studies.

Journal Articles

Positron lifetimes and mechanical properties of $$gamma$$-irradiated ultra high molecular weight polyethylene

Kobayashi, Yoshinori*; Yamawaki, Masato*; Oka, Toshitaka; Saiki, Seiichi; Mohamed, H.*; Hattori, Kanehisa*; Watanabe, Yoshihiro*

Materials Science Forum, 733, p.147 - 150, 2013/00

 Times Cited Count:3 Percentile:12.44

Positron annihilation lifetime spectroscopy (PALS) has widely been used for probing open volume defects in various materials. PALS is in principle non-destructive, yet conventional PALS is not strictly non-destructive because cutting out of two specimens from the material is required. Recently we developed a novel method of PALS, which is potentially applicable to non-destructive, onsite material inspection. In order to explore the possibility of onsite monitoring of polymer degradation by this novel method of PALS, we studied variations of positron lifetime and mechanical properties of ultra high molecular weight polyethylene (UHMWPE) subjected to $$gamma$$-irradiation. Correlations were found between the mechanical properties and o-Ps lifetimes, suggesting the feasibility of non-destructive, onsite monitoring of polymer degradation by PALS. The effect of $$gamma$$-irradiation on positronium formation is discussed.

Journal Articles

Lifetime of the unpaired electron species in calf thymus DNA thin films induced by nitrogen and oxygen K-shell photoabsorption

Oka, Toshitaka; Yokoya, Akinari; Fujii, Kentaro

International Journal of Radiation Biology, 88(12), p.884 - 887, 2012/12

 Times Cited Count:3 Percentile:68.79(Biology)

no abstracts in English

Journal Articles

Unpaired electron species in thin films of calf-thymus DNA molecules induced by nitrogen and oxygen K-shell photoabsorption

Oka, Toshitaka; Yokoya, Akinari; Fujii, Kentaro; Fukuda, Yoshihiro; Ukai, Masatoshi*

Physical Review Letters, 109(21), p.213001_1 - 213001_5, 2012/11

 Times Cited Count:10 Percentile:39.73(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Spectroscopic approaches to study DNA damage induced in genome exposed to ionizing radiation and its enzymatic repair

Yokoya, Akinari; Fujii, Kentaro; Oka, Toshitaka; Watanabe, Ritsuko

Hoshasen, 38(2), p.55 - 60, 2012/08

Journal Articles

Introduction to T$$_{rm E}$$X, 2; How to use it

Oka, Toshitaka; Ito, Kenji*

Hoshasen Kagaku (Internet), (93), p.57 - 61, 2012/03

no abstracts in English

Journal Articles

Foundations of radiation chemistry; Early processes of radiolysis by V. M. Byakov and S. V. Stepanov, 2

Kobayashi, Yoshinori*; Oka, Toshitaka

Hoshasen Kagaku (Internet), (93), p.47 - 56, 2012/03

no abstracts in English

Journal Articles

Spin-trapping reactions of a novel gauchetype radical trapper G-CYPMPO

Oka, Toshitaka; Yamashita, Shinichi; Midorikawa, Masamichi*; Saiki, Seiichi; Muroya, Yusa*; Kamibayashi, Masato*; Yamashita, Masayuki*; Anzai, Kazunori*; Katsumura, Yosuke*

Analytical Chemistry, 83(24), p.9600 - 9604, 2011/10

 Times Cited Count:23 Percentile:32.31(Chemistry, Analytical)

Chemical reactions of a novel gauche-type spin trap, G-CYPMPO ($textit{sc}$-5-(5,5-dimethyl-2-oxo-1,3,2-dioxaphosphinan-2-yl)-5-methy-1-pyrroline 1-oxide, torsion angle: O1-P1-C6-N1 of 52.8$$^{circ}$$), with reactive oxygen species were examined by pulse radiolysis technique with 35 MeV electron beam and electron spin resonance spectroscopy after $$^{60}$$Co $$gamma$$-ray irradiation. The spin trapping reaction rate constants of G-CYPMPO toward hydroxyl radical and hydrated electron were estimated to be (4.2$$pm$$0.1)$$times$$10$$^{9}$$ and (11.8$$pm$$0.2)$$times$$10$$^{9}$$ M$$^{-1}$$s$$^{-1}$$, respectively. Half-lives of spin adducts, hydroxyl radical and perhydroxyl radical adducted G-CYPMPO were estimated to be $$sim$$35 and $$sim$$90 min, respectively. A comparison of the results with earlier reports using different radical sources suggests that the purity of the solution and/or the radical generation technique may influence the stability of spin adducts.

Journal Articles

Foundations of radiation chemistry; Early processes of radiolysis by V. M. Byakov and S. V. Stepanov, 1

Kobayashi, Yoshinori*; Oka, Toshitaka

Hoshasen Kagaku (Internet), (92), p.39 - 49, 2011/09

Contents of the lecture note by Prof. V. M. Byakov and Dr. S. V. Stepanov (Institute of Theoretical and Experimental Physics, Russia) are described in a series of articles. The first article concerns basic concepts, classification and sources of ionizing radiations.

Journal Articles

Introduction to TeX, 1; How to install it

Oka, Toshitaka; Ito, Kenji*

Hoshasen Kagaku (Internet), (92), p.51 - 53, 2011/09

no abstracts in English

Journal Articles

Development of function-graded proton exchange membrane for PEFC using heavy ion beam irradiation

Shiraki, Fumiya*; Yoshikawa, Taeko*; Oshima, Akihiro*; Oshima, Yuji*; Takasawa, Yuya*; Fukutake, Naoyuki*; Oyama, Tomoko*; Urakawa, Tatsuya*; Fujita, Hajime*; Takahashi, Tomohiro*; et al.

Nuclear Instruments and Methods in Physics Research B, 269(15), p.1777 - 1781, 2011/08

 Times Cited Count:7 Percentile:43.84(Instruments & Instrumentation)

The graded energy deposition of heavy ion beam irradiation to polymeric materials was utilized to synthesize a novel proton exchange membrane (PEM) with the graded density of sulfonic acid groups toward the thickness direction. Stacked Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films were irradiated by Xe$$^{54+}$$ ion beam with the energy of 6 MeV/u under a vacuum condition. Irradiated films were grafted with styrene monomer and then sulfonated. The membrane electrode assembly (MEA) fabricated by the function graded PEM showed improved fuel cell performance in terms of voltage stability. It was expected that the function-graded PEM could control the graded concentration of sulfonic acid groups in PEM.

Journal Articles

Electron paramagnetic resonance study of unpaired electron species in thin films of pyrimidine bases induced by nitrogen and oxygen K-shell photoabsorption

Oka, Toshitaka; Yokoya, Akinari; Fujii, Kentaro

Applied Physics Letters, 98(10), p.103701_1 - 103701_3, 2011/03

 Times Cited Count:6 Percentile:68.36(Physics, Applied)

In order to clarify the mechanism of DNA-base modification induced by K-shell photoabsorption of nitrogen and oxygen atoms, we measured EPR spectra of two DNA pyrimidine bases, thymine and cytosine. The $$g$$-factor of 2.000 of the unpaired electron species arising only during irradiation is determined. The EPR intensities for cytosine are two times larger than those simply estimated based on the photoabsorption cross section, whereas those for thymine show similar energy dependence to photoabsorption spectra, suggesting that cytosine favors to form unpaired electron species, rather than thymine, presumably due to capturing photo- or Auger electrons emitted by photo-absorbing atoms. Cytosine residue in DNA may play a role as an "electron reservoir" just after photoelectric effect.

Journal Articles

Study on depth profile of heavy ion irradiation effects in poly(tetrafluoroethylene-co-ethylene)

Gowa, Tomoko*; Shiotsu, Tomoyuki*; Urakawa, Tatsuya*; Oka, Toshitaka; Murakami, Takeshi*; Oshima, Akihiro*; Hama, Yoshimasa*; Washio, Masakazu*

Radiation Physics and Chemistry, 80(2), p.264 - 267, 2011/02

 Times Cited Count:6 Percentile:48.94(Chemistry, Physical)

High linear energy transfer (LET) heavy ion beams were irradiated to poly(tetrafluoroethylene-co-ethylene) (ETFE) under vacuum and in air. The irradiation effects in ETFE as a function of the depth was precisely evaluated by analyzing each one of the films of the irradiation samples which were made of stacked ETFE films. It was indicated that conjugated double bonds would be generated by heavy ion beam irradiation, and their amounts should show the Bragg-curve-like distributions. Also, it was suggested that higher LET beams would induce radical formation in high density and longer conjugated C=C double bonds could be generated by the second-order reactions. Moreover, for irradiation samples in air, C=O was produced correlating to the yield of oxygen molecules diffusing from the sample surface.

Journal Articles

Changes to the chemical structure of isotactic-polypropylene induced by ion-beam irradiation

Oka, Toshitaka; Oshima, Akihiro*; Motohashi, Ryota*; Seto, Naoto*; Watanabe, Yuji*; Kobayashi, Ryoji*; Saito, Koki*; Kudo, Hisaaki*; Murakami, Takeshi*; Washio, Masakazu*; et al.

Radiation Physics and Chemistry, 80(2), p.278 - 280, 2011/02

 Times Cited Count:6 Percentile:48.94(Chemistry, Physical)

The chemical structures of various ion-beam irradiated isotactic-polypropylene samples were studied. Results of micro-Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy suggest not only the linear energy transfer, but also the fluence is effective in local transformation of the isotactic-polypropylene.

Journal Articles

Ortho-positronium reactions in water studied by positron annihilation age-momentum correlation

Hirade, Tetsuya; Oka, Toshitaka; Lee, J.

Materials Science Forum, 666, p.103 - 108, 2011/01

OH radical formed in water by ionizing radiations is very strong active oxygen and has very short lifetime. There was no methods of direct observation of the OH radical, but it is becoming possible to observe it by ortho-positronium, because of the existence of reaction between OH radical and ortho-positronium. Positron annihilation age-momentum correlation measurement (AMOC) is the best method to detect the ortho-positronium reactions. We investigated the temperature dependence of OH radical reaction and found out that The reaction is faster at higher temperatures probably because of the faster diffusion.

Journal Articles

High-rate crystallization of polycarbonate in spincast thin film

Ata, Seisuke*; Oka, Toshitaka; He, C.-Q.*; Odaira, Toshiyuki*; Suzuki, Ryoichi*; Ito, Kenji*; Kobayashi, Yoshinori*; Ougizawa, Toshiaki*

Journal of Polymer Science, Part B; Polymer Physics, 48(20), p.2148 - 2153, 2010/10

 Times Cited Count:3 Percentile:87.25(Polymer Science)

Surface morphology of bisphenol-A polycarbonate (BAPC) thin films with thickness ranging from 30 to 1000 nm on silicon substrates was studied by atomic force microscopy (AFM). The films were prepared by spincasting from 1,2-dichloroethane solutions of 0.25-5.0 wt % BAPC. Even though longer annealing than 250 h was necessary for complete crystallization for bulk BAPC, high crystallinity was observed for 30 nm thick film after annealing at 200 $$^{circ}$$C for 48 h in vacuum. Positron annihilation lifetime spectroscopy (PALS) measurements showed that the free volume hole size in 30 nm thick film was larger than that of bulk at 200 $$^{circ}$$C. Comparison of the BAPC concentration in the precursor solution with the overlap concentration suggests that the high crystallinity of the 30 nm BAPC film is due to less entangled chains caused by rapid removal of the solvent from the dilute solution.

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