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Journal Articles

Dense radical formation in L-alanine-3,3,3-d3 and L-alanine-d4 by 1.5 keV soft X-ray irradiation

Nakagawa, Seiko*; Oka, Toshitaka; Fujii, Kentaro*; Yokoya, Akinari*

Radiation Physics and Chemistry, 192, p.109884_1 - 109884_5, 2022/03

Radicals produced in crystalline L-alanine-3,3,3-d3 and L-alanine-d4 were observed by the electron spin resonance (ESR) technique during 1.5 keV soft X-ray irradiation. The line width of the ESR spectra obtained by the soft X-ray irradiation was 1.5 times wider than that of hard X-rays from a previous report, meaning a higher density of radicals. The efficiency of the radical yield by the soft X-ray irradiation was 10$$^{-6}$$ relative to that by $$gamma$$-irradiation. For the soft X-ray irradiation, many radicals will be lost by the efficient radical-radical recombination due to the higher density of the radicals, just as the high-LET irradiation by heavy ions. We concluded that the high LET nature of the lower energy photons leads to the dense radical formation in the crystalline alanine powder.

Journal Articles

Design for detecting recycling muon after muon-catalyzed fusion reaction in solid hydrogen isotope target

Okutsu, Kenichi*; Yamashita, Takuma*; Kino, Yasushi*; Nakashima, Ryota*; Miyashita, Konan*; Yasuda, Kazuhiro*; Okada, Shinji*; Sato, Motoyasu*; Oka, Toshitaka; Kawamura, Naritoshi*; et al.

Fusion Engineering and Design, 170, p.112712_1 - 112712_4, 2021/09

A muonic molecule which consists of two hydrogen isotope nuclei (deuteron (d) or tritium (t)) and a muon decays immediately via nuclear fusion and the muon will be released as a recycling muon, and start to find another hydrogen isotope nucleus. The reaction cycle continues until the muon ends up its lifetime of 2.2 $$mu$$s. Since the muon does not participate in the nuclear reaction, the reaction is so called a muon catalyzed fusion ($$mu$$CF). The recycling muon has a particular kinetic energy (KE) of the muon molecular orbital when the nuclear reaction occurs. Since the KE is based on the unified atom limit where distance between two nuclei is zero. A precise few-body calculation estimating KE distribution (KED) is also in progress, which could be compared with the experimental results. In the present work, we observed recycling muons after $$mu$$CF reaction.

Journal Articles

Time evolution calculation of muon catalysed fusion; Emission of recycling muons from a two-layer hydrogen film

Yamashita, Takuma*; Okutsu, Kenichi*; Kino, Yasushi*; Nakashima, Ryota*; Miyashita, Konan*; Yasuda, Kazuhiro*; Okada, Shinji*; Sato, Motoyasu*; Oka, Toshitaka; Kawamura, Naritoshi*; et al.

Fusion Engineering and Design, 169, p.112580_1 - 112580_5, 2021/08

A muon ($$mu$$) having 207 times larger mass of electron and the same charge as the electron has been known to catalyze a nuclear fusion between deuteron (d) and triton (t). These two nuclei are bound by $$mu$$ and form a muonic hydrogen molecular ion, dt$$mu$$. Due to the short inter-nuclear distance of dt$$mu$$, the nuclear fusion, d +t$$rightarrow alpha$$ + n + 17.6 MeV, occurs inside the molecule. This reaction is called muon catalyzed fusion ($$mu$$CF). Recently, the interest on $$mu$$CF is renewed from the viewpoint of applications, such as a source of high-resolution muon beam and mono-energetic neutron beam. In this work, we report a time evolution calculation of $$mu$$CF in a two-layered hydrogen isotope target.

Journal Articles

Rapid analysis of $$^{90}$$Sr in cattle bone and tooth samples by inductively coupled plasma mass spectrometry

Koarai, Kazuma; Matsueda, Makoto; Aoki, Jo; Yanagisawa, Kayo*; Terashima, Motoki; Fujiwara, Kenso; Kino, Yasushi*; Oka, Toshitaka; Takahashi, Atsushi*; Suzuki, Toshihiko*; et al.

Journal of Analytical Atomic Spectrometry, 36(8), p.1678 - 1682, 2021/08

 Times Cited Count:0 Percentile:0.02(Chemistry, Analytical)

Rapid analysis of $$^{90}$$Sr in bone and tooth samples of cattle were achieved by an inductively coupled plasma mass spectrometry (ICP-MS) coupled with mass shift and solid phase extraction techniques. Limit of detection (LOD) in the ICP-MS measurement of 0.1 g samples was lower than that of the radioactivity measurement. Analytical time of the ICP-MS method was reduced from 20 days to 11 hours, compared with the radiometric method. Therefore, the ICP-MS method can be rapid and useful procedure of $$^{90}$$Sr in small bone and tooth samples derived from terrestrial animals.

Journal Articles

Radioactivity and radionuclides in deciduous teeth formed before the Fukushima-Daiichi Nuclear Power Plant accident

Takahashi, Atsushi*; Chiba, Mirei*; Tanahara, Akira*; Aida, Jun*; Shimizu, Yoshinaka*; Suzuki, Toshihiko*; Murakami, Shinobu*; Koarai, Kazuma; Ono, Takumi*; Oka, Toshitaka; et al.

Scientific Reports (Internet), 11(1), p.10355_1 - 10355_11, 2021/05

 Times Cited Count:1 Percentile:65.97(Multidisciplinary Sciences)

Journal Articles

Morphological reproductive characteristics of testes and fertilization capacity of cryopreserved sperm after the Fukushima accident in raccoon (${it Procyon lotor}$)

Komatsu, Kazuki*; Iwasaki, Tsugumi*; Murata, Kosuke*; Yamashiro, Hideaki*; Goh, V. S. T.*; Nakayama, Ryo*; Fujishima, Yohei*; Ono, Takumi*; Kino, Yasushi*; Shimizu, Yoshinaka*; et al.

Reproduction in Domestic Animals, 56(3), p.484 - 497, 2021/03

We have established an archive system of livestock and wild animals from the surrounding ex-evacuation zone. Wildlife within the alert zone have been exposed to low-dose-rate (LDR) radiation for a long and continuous time. In this study, we analysed the morphological characteristics of the testes and in vitro fertilization (IVF) capacity of cryopreserved sperm of raccoons from the ex-evacuation zone of the FDNPP accident. This study revealed that the chronic and LDR radiation exposure associated with the FDNPP accident had no adverse effect on the reproductive characteristics and functions of male raccoons.

Journal Articles

Development of a method for positron annihilation lifetime measurement in thin polyethylene films using a Na-22 source

Yamawaki, Masato*; Uesugi, Naoya*; Oka, Toshitaka; Nagasawa, Naotsugu*; Ando, Hirokazu*; O'Rourke, B. E.*; Kobayashi, Yoshinori*

Japanese Journal of Applied Physics, 59(11), p.116504_1 - 116504_5, 2020/11

Positron annihilation lifetime measurements were performed on polyethylene films with thickness of 15$$mu$$m - 2000$$mu$$m using a Na-22 positron source enclosed in a Kapton film. For thin films, some positrons will pass through the film and annihilate behind it. Using a single film in a commercial anti-coincidence system, by placing an annealed stainless steel (SUS304) cover behind the sample, it is possible to sufficiently measure the long lifetime ortho-positronium (o-Ps) component even in thin films. Additionally, calculated intensities of the o-Ps component determined from the estimated film transmittance agreed well with the measured values. Furthermore, by applying this method to uniaxially stretched UHMWPE, we were able to observe structural changes owing to the stretching consistent with shorter measured o-Ps lifetime and increased o-Ps intensity.

Journal Articles

External dose estimation for wild animals using ESR spectroscopy

Oka, Toshitaka; Takahashi, Atsushi*

Hoshasen Kagaku (Internet), (110), p.13 - 19, 2020/10

The article depicts how to estimate the external exposure dose for wild animals using electron spin resonance (ESR) spectroscopy. The relationship between the CO$$_{2}$$ radical intensity and the absorbed dose, that is, dose response curve of tooth enamel of Japanese macaque was observed, and the detection limit of our method was estimated. The estimated detection limit of 33.5 mGy is comparable to the previously reported detection limit for human molar teeth. The external exposure dose for seven wild Japanese macaques captured in Fukushima prefecture were examined using this dose response curve. The estimated external exposure dose were ranged between 45 mGy to 300 mGy.

Journal Articles

A Fault dating method using an electron spin resonance

Tanaka, Kiriha*; Muto, Jun*; Nagahama, Hiroyuki*; Oka, Toshitaka

Hoshasen Kagaku (Internet), (110), p.21 - 30, 2020/10

In a fault dating by electron spin resonance (ESR), the number of unpaired electrons trapped in defects in minerals contained in a fault material is detected as ESR intensity. Based on the quantitative change of the intensity before and after an earthquake, the last age of a fault movement can be estimated. However, this method has a hypothesis called "zero-setting" which assumes the decrease in the ESR intensity to zero by fault movement during an earthquake. In order to understand and demonstrate zero-setting, the analysis of the natural fault materials and experiments mimicking fault movements have been conducted. In this paper, we summarized the previous studies about zero-setting by fault movement and described the current status and challenges.

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

 Times Cited Count:1 Percentile:39.17(Nuclear Science & Technology)

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

 Times Cited Count:4 Percentile:47.91(Geochemistry & Geophysics)

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

Introduction of the research using radioisotopes and radiation; How to be a researcher,1; Self-discipline, just do research

Oka, Toshitaka

Nihon Aisotopu Kyokai Homu Peji (Internet), 1 Pages, 2019/09

To involve young people in the research using radiation/isotopes, we explained why we started such research.

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:4 Percentile:85.56

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:95.56

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:85.38

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:28.72(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:11 Percentile:60.72(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

118 (Records 1-20 displayed on this page)