Nature of the physicochemical process in water photolysis uncovered by a computer simulation

Kai, Takeshi; Toigawa, Tomohiro; Ukai, Masatoshi*; Fujii, Kentaro*; Watanabe, Ritsuko*; Yokoya, Akinari*

Journal of Chemical Physics, 158(16), p.164103_1 - 164103_8, 2023/04

New insight into water radiolysis and photolysis is indispensable in the dramatic progress of sciences and technologies in various research areas. In the radiation field, reactive hydrated electrons are considerably produced along radiation tracks. Although the formation results from a transient dynamic correlation between ejected electrons and water, the individual mechanisms of electron thermalization, delocalization, and polarization are unknown. Using a dynamic Monte Carlo code, we show herein that the ejected electrons are immediately delocalized by molecular excitations in parallel with phonon polarization and gradually thermalized by momentum transfer with an orientation polarization in a simultaneous manner. Our results show that these mechanisms heavily depend on the intermolecular vibration and rotation modes peculiar to water. We expect our approach to be a powerful technique for connecting physical and chemical processes in various solvents.

Spallation and fragmentation cross sections for 168 MeV/nucleon Xe ions on proton, deuteron, and carbon targets

Sun, X. H.*; Wang, H.*; Otsu, Hideaki*; Sakurai, Hiroyoshi*; Ahn, D. S.*; Aikawa, Masayuki*; Fukuda, Naoki*; Isobe, Tadaaki*; Kawakami, Shunsuke*; Koyama, Shumpei*; et al.

Physical Review C, 101(6), p.064623_1 - 064623_12, 2020/06

https://doi.org/10.1103/PhysRevC.101.064623

The spallation and fragmentation reactions of Xe induced by proton, deuteron and carbon at 168 MeV/nucleon were studied at RIKEN Radioactive Isotope Beam Factory via the inverse kinematics technique. The cross sections of the lighter products are larger in the carbon-induced reactions due to the higher total kinetic energy of carbon. The energy dependence was investigated by comparing the newly obtained data with previous results obtained at higher reaction energies. The experimental data were compared with the results of SPACS, EPAX, PHITS and DEURACS calculations. These data serve as benchmarks for the model calculations.

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.

Science, 364(6437), p.272 - 275, 2019/04

https://doi.org/10.1126/science.aav7432

The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

A Significant role of non-thermal equilibrated electrons in the formation of deleterious complex DNA damage

Kai, Takeshi; Yokoya, Akinari*; Ukai, Masatoshi*; Fujii, Kentaro*; Toigawa, Tomohiro; Watanabe, Ritsuko*

Physical Chemistry Chemical Physics, 20(4), p.2838 - 2844, 2018/01

https://doi.org/10.1039/C7CP06903K

It is thought that complex DNA damage which induces in radiation biological effects is formed at radiation track end. Thus, the earliest stage of water radiolysis at the electron track end was studied to predict DNA damage. These results indicate that DNA damage sites comprising multiple nucleobase lesions with a single strand breaks can therefore be formed by multiple collisions of the electrons within three base pairs (3bp) of a DNA strand. This multiple damage site cannot be processed by base excision repair enzymes. However, pre-hydrated electrons can also be produced resulting in an additional base lesion more than 3bp away from the multi-damage site. This clustered damage site may be finally converted into a double strand break (DSB) when base excision enzymes process the additional base lesions. These DSBs include another base lesion(s) at their termini that escape from the base excision process and which may result in biological effects such as mutation in surviving cells.

Dynamic behavior of secondary electrons in liquid water at the earliest stage upon irradiation; Implications for DNA damage localization mechanism

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

Journal of Physical Chemistry A, 120(42), p.8228 - 8233, 2016/10

https://doi.org/10.1021/acs.jpca.6b05929

Low energy secondary electrons produced by an ionizing radiation in a living cell may involve in formation of complexed DNA damage. We performed theoretical study for numerical calculation of dynamic behavior of the electrons to imply a formation of radiation damage to DNA. The decelerating electrons are gradually attracted to their parent cations by the Coulombic force within hundreds of fs, and about 12.6 % of electrons are finally distributed within 2 nm from the cations. The collision fraction of the ionization and excitation within 1 nm from the cation was estimated to be about 40 %. From those analyses, we suggested a process of DNA damage that the secondary electrons may cause highly localized lesions around a cation in DNA molecule through additional dissociative electron transfer as well as the ionization or the excitation if the electrons are ejected from DNA. The localized damage may involve ultimately in biological effects such as cell death or mutation induction.

Recent progress of radiation physicochemical process (second part)

Kai, Takeshi; Yokoya, Akinari*; Fujii, Kentaro*; Watanabe, Ritsuko*

Hoshasen Kagaku (Internet), (102), p.49 - 56, 2016/00

Behavior analysis of low energy electrons in liquid water provides the fundamentals for successive radiation chemistry, and it makes analysis of DNA damage implication involved in the electrons possible. We have progressed theoretical studies for radiation physicochemical process of water to clear the role of secondary electrons damage to DNA. The process has included many unknown factors for the DNA damage so far. We implied a newly formation process of unrepair DNA damage produced by the secondary electrons. We report our outcomes separately in three manuscripts entitled "Recent progress of radiation physicochemical process (first, second, third parts)". In this second part, we show calculated results of thermalization lengths and times of electrons in water to verify a dynamic Monte Carlo code developed in this study. From the calculated results, we also report our prediction, which are different from previous one, for thermalization and pre-hydration processes.

Report for "FY 2013 Evaluation of Decontamination Technology Demonstrations Projects for the environmental remediation with radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant Accident" (Contract research)

Watanabe, Masahisa; Tagawa, Akihiro; Umemiya, Noriko; Maruyama, Noboru; Yoshida, Mami; Kawase, Keiichi; Noguchi, Shinichi; Sakazume, Yoshinori; Watanabe, Masanori; Hiraga, Hayato; et al.

JAEA-Review 2014-028, 184 Pages, 2014/10

JAEA-Review-2014-028.pdf:37.79MB

JAEA received technical proposals from private enterprise about techniques that can be used for decontamination work, and "Decontamination Technology Demonstrations Projects" was commissioned from the Ministry of the Environment to verifies the decontamination effect, economy feasibility, safety, and other factors. By the "FY 2013 Decontamination Technology Demonstrations Projects" JAEA carried out technical advice of demonstration test and evaluation of 11 technologies (e.g., decontamination of soils and green space and wastes and washing of fly ash).

Report for "FY 2012 Evaluation of Decontamination Technology Demonstrations Projects for the environmental remediation with radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant Accident" (Contract research)

Watanabe, Masahisa; Umemiya, Noriko; Tagawa, Akihiro; Kawase, Keiichi; Noguchi, Shinichi; Sakazume, Yoshinori; Watanabe, Masanori; Tokizawa, Takayuki

JAEA-Review 2013-052, 232 Pages, 2014/03

JAEA-Review-2013-052.pdf:26.42MB

To discover technologies that can be utilized for decontamination work and verify their effects, economic feasibility, safety, and other factors, the Cabinet Office, Government of Japan launched the FY2012 Decontamination Technology Demonstrations Project to publicly solicit decontamination technologies that would be verified in demonstration tests and adopted 15 candidates. JAEA was commissioned by the Ministry of the Environment, Government of Japan to provide technical assistance related to these demonstrations. JAEA carried out technical advice of demonstration test and evaluation of 15 technologies (e.g., decontamination technology of Burned ash washing and Pond Dredging) to perform decontamination of the environment.

Structural analyses of HV bushing for ITER heating NB system

Tobari, Hiroyuki; Inoue, Takashi; Taniguchi, Masaki; Kashiwagi, Mieko; Umeda, Naotaka; Dairaku, Masayuki; Yamanaka, Haruhiko; Watanabe, Kazuhiro; Sakamoto, Keishi; Kuriyama, Masaaki*; et al.

Fusion Engineering and Design, 88(6-8), p.975 - 979, 2013/10

https://doi.org/10.1016/j.fusengdes.2013.02.020

The HV bushing, one of the ITER NB components, which is to be procured by JADA, is a multi-conductor feed through composed of five-stage double-layered insulator columns with large brazed ceramic ring and fiber reinforced plastic (FRP) ring. The HV bushing is a bulk head between insulation gas at 0.6 MPa and vacuum. The FRP ring is required to sustain the pressure load, seismic load and dead weight. Brazing area of the ceramic ring with Kovar is required to maintain vacuum leak tightness and pressure tightness against the air filled at 0.6 MPa. To design the HV bushing satisfying the safety factor of 3.5, mechanical analyses were carried out. As for the FRP ring, it was confirmed that isotropic fiber cloth FRP rings should be used for sufficient strength against shear stress. Also, shape and fixation area of the Kovar sleeve were modified to lower the stress at the joint area. As a result, a design of the insulator for the HV bushing was established satisfying the requirement.

Effect of non-uniform electron energy distribution function on plasma production in large arc driven negative ion source

Shibata, Takanori; Koga, Shojiro*; Terasaki, Ryo*; Inoue, Takashi; Dairaku, Masayuki; Kashiwagi, Mieko; Taniguchi, Masaki; Tobari, Hiroyuki; Tsuchida, Kazuki; Umeda, Naotaka; et al.

Review of Scientific Instruments, 83(2), p.02A719_1 - 02A719_3, 2012/02

https://doi.org/10.1063/1.3673485

In the NBI for large fusion devices, production of uniform negative ion beam is one of important issues. A physical model is proposed to understand the non-uniformity. It has been qualitatively shown that the non-uniform beam intensity is due to the following process; (1) formation of non-uniform EEDF, (2) localized production of hydrogen atoms/ions (H/H) due to (1), (3) non-uniform flux of H/H to the PG and (4) localized surface production of negative ions. However, in the past studies, the EEDF was assumed as two temperature Maxwellian distribution from measurements. Thus effects of high energy electrons are not taken into account precisely. In the present research, local EEDF is calculated by the 3D Monte-Carlo kinetic model which takes into account the spatial and magnetic configurations of the real negative ion source. The numerical result show that high energy component of the EEDF enhances the spatial non-uniformity in the production rate of H/H.