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Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke*; Hirata, Yuho; Tezuka, Tomoya*; Tsuchida, Hidetsugu*; Yokoya, Akinari*
Scientific Reports (Internet), 14, p.24722_1 - 24722_15, 2024/10
Scientific insight of water radiolysis is essential to estimate the direct and indirect effects of radiation DNA damage. Secondary electrons produced by water radiolysis are responsible for both effects. Here, we use a first-principles code to calculate the femtosecond dynamics of secondary electrons produced as a result of 20-30 eV energy deposition to water and analyze the formation mechanism of radiolytic chemical species produced in a nano-size ultra-small space region. From the results, it was clarified that the chemical species produced by water radiolysis begin to densify in the ultra-small region of a few nanometers when the deposition energy exceeds 25 eV. Our results provide important scientific insights into the formation of clustered DNA damage, which is believed to cause biological effects such as cell death.
Toigawa, Tomohiro; Kai, Takeshi; Kumagai, Yuta; Yokoya, Akinari*
Journal of Chemical Physics, 160(21), p.214119_1 - 214119_9, 2024/06
Times Cited Count：0 Percentile：0.00(Chemistry, Physical)The spur reaction is crucial for determining radiolysis or photolysis in liquid, but the spur expansion process has yet to be elucidated. One reason is the need to understand the role of the dielectric response of the solvating molecules surrounding the charged species generated by ionization. The dielectric response corresponds to the time evolution of the permittivity and might affect the chemical reaction-diffusion of the species in a spur expansion process. This study examined the competitive relationship between reaction-diffusion kinetics and the dielectric response by solving the Debye-Smoluchowski equation while considering the dielectric response. The Coulomb force between the charged species gradually decreases with the dielectric response. Our calculation results found a condition where fast recombination occurs before the dielectric response is complete. Although it has been reported that the primary G-values of free electrons depend on the static dielectric constant under low-linear-energy transfer radiation-induced ionization, we propose that considering the dielectric response can provide a deeper insight into fast recombination reactions under high-linear-energy transfer radiation- or photo-induced ionization. Our simulation method enables the understanding of fast radiation-induced phenomena in liquids.
Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke; Hirata, Yuho; Tezuka, Tomoya*; Tsuchida, Hidetsugu*; Yokoya, Akinari*
RSC Advances (Internet), 13(46), p.32371 - 32380, 2023/11
Times Cited Count：1 Percentile：20.85(Chemistry, Multidisciplinary)Although scientific knowledge of photolysis and radiolysis of water is widely used in the life sciences and other fields, the formation mechanism of the spatial distribution of hydrated electrons (spur) resulting from energy deposition to water is still not well understood. The chemical reaction times of hydrated electrons, OH radicals, and H
O
in the spur strongly depend on the spur radius. In our previous study, we elucidated the mechanism at a specific given energy (12.4 eV) by first-principles calculations. In the present study, we performed first-principles calculations of the spur radius at the deposition energies of 11-19 eV. The calculated spur radius is 3-10 nm, which is consistent with the experimental prediction (~4 nm) for the energy range of 8-12.4 eV, and the spur radius gradually increases with increasing energy. The spur radius is a new scientific knowledge and is expected to be widely used for estimating radiation DNA damage.
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
Times Cited Count：3 Percentile：61.71(Chemistry, Physical)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.
Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke*; Hirata, Yuho; Tezuka, Tomoya*; Tsuchida, Hidetsugu*; Yokoya, Akinari*
RSC Advances (Internet), 13(11), p.7076 - 7086, 2023/03
Times Cited Count：4 Percentile：62.38(Chemistry, Multidisciplinary)Scientific insights of water radiolysis are widely used in the life sciences and so on, however, the formation mechanism of radicals, a product of water radiolysis, is still not well understood. We are challenging to develop a simulation code to solve this formation mechanism from the viewpoint of radiation physics. Our first-principles calculations have revealed that the behavior of secondary electrons in water is governed not only by collisional effects but also by polarization effects. Furthermore, from the predicted ratio of ionization to electronic excitation, based on the spatial distribution of secondary electrons, we successfully reproduce the initial yield of hydrated electrons predicted in terms of radiation chemistry. The code provides us a reasonable spatiotemporal connection from radiation physics to radiation chemistry. Our findings are expected to provide newly scientific insights for understanding the earliest stages of water radiolysis.
Toigawa, Tomohiro; Kumagai, Yuta; Yamashita, Shinichi*; Ban, Yasutoshi; Matsumura, Tatsuro
UTNL-R-0502 (Internet), 2 Pages, 2022/04
This report summarizes the results obtained in FY2020 at the Electron Linac Facility of the University of Tokyo. The radiolysis process of 
-hexaoctyl nitrilotriacetamide (HONTA), which is expected to be used as an extractant in a separation process for minor actinides, diluted in dodecane was investigated by pulse radiolysis experiments. The radical cation and the triplet-excited state of HONTA were observed in the nanosecond time region. The transition from the radical cation to the triplet excited state was slowed down by adding electron scavengers, and further, the reactivity of the triplet excited state was also suppressed.
-octylnitrilo-triacetamide (HONTA) complexes of americium and europiumToigawa, Tomohiro; Peterman, D. R.*; Meeker, D. S.*; Grimes, T. S.*; Zalupski, P. R.*; Mezyk, S. P.*; Cook, A. R.*; Yamashita, Shinichi*; Kumagai, Yuta; Matsumura, Tatsuro; et al.
Physical Chemistry Chemical Physics, 23(2), p.1343 - 1351, 2021/01
Times Cited Count：15 Percentile：78.83(Chemistry, Physical)The candidate An(III)/Ln(III) separation ligand hexa--octylnitrilo-triacetamide (HONTA) was irradiated under envisioned SELECT (Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation) process conditions using a solvent test loop in conjunction with cobalt-60 gamma irradiation. We demonstrate that HONTA undergoes exponential decay with increasing gamma dose to produce a range of degradation products which have been identified and quantified by HPLC-ESI-MS/MS techniques. The combination of HONTA destruction and degradation product ingrowth, particularly dioctylamine, negatively impacts the extraction and back-extraction of both americium and europium ions. The loss of HONTA was attributed to its reaction with the solvent (
-dodecane) radical cation of 
(HONTA + R
) = (7.61 
0.82) 
10
M
s obtained by pulse radiolysis techniques. However, when this ligand is bound to either americium or europium ions, the observed -dodecane radical cation kinetics increase by over an order of magnitude. This large reactivity increase to additional reaction pathways occurring upon metal-ion binding. Lastly nanosecond time-resolved measurements showed that both direct and indirect HONTA radiolysis yielded the short-lived (
100 ns) HONTA radical cation as well as a longer-lived (
s) HONTA triplet excited state. These HONTA species are important precursors to the suite of HONTA degradation products observed.
Toigawa, Tomohiro; Tsubata, Yasuhiro; Kai, Takeshi; Furuta, Takuya; Kumagai, Yuta; Matsumura, Tatsuro
Solvent Extraction and Ion Exchange, 39(1), p.74 - 89, 2021/00
Times Cited Count：2 Percentile：8.54(Chemistry, Multidisciplinary)Absorbed-dose estimation is essential for evaluation of the radiation feasibility of minor-actinide-separation processes. We propose a dose-evaluation method based on radiation permeability, with comparisons of heterogeneous structures seen in the solvent-extraction process, such as emulsions forming in the mixture of the organic and aqueous phases. A demonstration of radiation-energy-transfer simulation is performed with a focus on the minor-actinide-recovery process from high-level liquid waste with the aid of the Monte Carlo radiation-transport code PHITS. The simulation results indicate that the dose absorbed by the extraction solvent from alpha ray depends upon the emulsion structure, and that from beta and gamma ray depends upon the mixer-settler-apparatus size. Non-negligible contributions of well-permeable gamma rays were indicated in terms of the plant operation of the minor-actinide-separation process.
Toigawa, Tomohiro; Murayama, Rin*; Kumagai, Yuta; Yamashita, Shinichi*; Suzuki, Hideya; Ban, Yasutoshi; Matsumura, Tatsuro
UTNL-R-0501, p.24 - 25, 2020/12
This report summarizes the results obtained in FY2019 at Electron Linac Facility of University of Tokyo. The radiolysis process of a diglycolamide extractant, which is expected to be used in the separation process of minor actinides (MA), in dodecane and octanol solutions was investigated by pulse radiolysis. As a result, it was suggested that by adding alcohol, the decomposition process of the diglycolamide extractant was different from the decomposition processes in the single solvent of dodecane considered that the decomposition occurred via a radical cation species of the extractant.
Kai, Takeshi; Yokoya, Akinari*; Ukai, Masatoshi*; Fujii, Kentaro*; Toigawa, Tomohiro; Watanabe, Ritsuko*
Physical Chemistry Chemical Physics, 20(4), p.2838 - 2844, 2018/01
Times Cited Count：24 Percentile：76.69(Chemistry, Physical)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.
Kumagai, Yuta; Toigawa, Tomohiro; Yamashita, Shinichi*; Matsumura, Tatsuro
no journal, ,
Ionizing radiation induces degradation of organic molecules. This action of ionizing radiation needs to be incorporated in designing and safety evaluation of solvent extraction processes for separation of radioactive elements. A reliable estimation of the effect of radiolysis requires understanding of the degradation mechanism as well as basic data regarding the extractant degradation and its radiolytic products. This study focuses on a promising extractant for separation of actinides from lanthanides, 
,,',','',''- hexaoctyl- nitrilotriacetamide (HONTA). We have investigated the radiolysis of HONTA by LC-MS/MS analysis of radiolytic products of HONTA and by UV-visible spectroscopy of its radical transient using pulse radiolysis technique. In these experiments, radiolysis of neat HONTA and that of HONTA in dodecane solvent are compared in order to understand the degradation mechanism.
Masuda, Ryotaro*; Otaka, Saki*; Gejo, Tatsuo*; Takeuchi, Satoshi*; Adachi, Junichi*; Hoshino, Masamitsu*; Toigawa, Tomohiro; Miyazaki, Yasunori; Sano, Yuichi; Takeuchi, Masayuki
no journal, ,
no abstracts in English
Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke; Hirata, Yuho; Tezuka, Tomoya*; Tsuchida, Hidetsugu*; Ito, Yuma*; Yokoya, Akinari*
no journal, ,
Irradiation of living systems forms complex DNA damage that induces biological effects in very rare cases. This complex DNA damage is called cluster damage and is very difficult to detect experimentally. In this study, we have developed physical and chemical codes for analyzing DNA damage, and are working to elucidate the formation mechanism of cluster damage. In this study, we analyzed the results of calculations in a simple system in which energy is deposited to DNA and secondary electrons are emitted, and showed that the formation mechanism of cluster damage strongly depends on the deposition energy to DNA. This scientific insight is expected to contribute to the elucidation of the repair mechanism of DNA damage and lead to the elucidation of radiation biological effects.
Toigawa, Tomohiro; Tsubata, Yasuhiro; Kai, Takeshi; Kimura, Takahiro; Matsumura, Tatsuro
no journal, ,
To evaluate the feasibility of the solvent extraction process, absorbed dose of each quality of radiation for extraction solvents were estimated by using a Monte Carlo Particle and Heavy Ion Transport code System, PHITS. Our results suggest that low LET radiation will be dominant influence on absorbed dose. It was demonstrated the degradation yields of the extractants and the generation yields of the degradation products could be evaluated by reference to the experimentally obtained G-values.
measurement method for radioactive waste analysisKumagai, Yuta; Kawai, Masashi*; Ikarugi, Riko; Oka, Toshitaka; Toigawa, Tomohiro; Kitatsuji, Yoshihiro; Kumagai, Jun*
no journal, ,
We have developed a highly sensitive H analysis method by employing a gas chromatograph with a senser diode, aiming to apply for small amounts of H production from radioactive wastes. The H analysis method was tested with an X-ray irradiation experiment of NaWO
2HO. Even though the absorbed dose was less than 100 Gy, the H production from only 1 g of the sample can be analyzed by our method. Based on the experimental results, the lower limit of H quantification was evaluated to be 2 10
mol.
radiolysis of an extractant for minor actinides, Hexaoctyl-nitrilotriacetamide (HONTA), in dodecane diluentToigawa, Tomohiro; Suzuki, Hideya; Ban, Yasutoshi; Ishii, Sho*; Matsumura, Tatsuro
no journal, ,
Radiolytic stability of an extractant, N,N,N',N',N'',N''-hexaoctyl-nitrilotriacetamide (HONTA), for separation between minor actinides and rare-earth elements were investigated by using -ray emitting from cobalt-60. Degradation amount of HONTA and its products yields were obtained by gas chromatographic analysis. Our results showed the cleavage sites in HONTA radiolysis and suggested that the radiolysis of HONTA was ruled by different mechanism depending on the absorbed dose.
-radiolysis of MA separation agent of HONTA on extraction performanceToigawa, Tomohiro; Suzuki, Hideya; Ban, Yasutoshi; Ishii, Sho*; Matsumura, Tatsuro
no journal, ,
To evaluate the radiolytic stability of a novel tetradentate extractant of N, N, N', N', N", N"-hexaoctyl-nitrilotriacetamide (HONTA), batch extractions of lanthanide (Ln) elements were performed by using -irradiated HONTA extraction solvents. The distribution ratios decreased exponentially with increasing the absorbed dose, and no difference between Ln could be observed. These indicate that the degradation products of HONTA did not act as Ln extractants, and the decay of Ln extraction were caused by degradation of HONTA.
Toigawa, Tomohiro; Tsubata, Yasuhiro; Matsumura, Tatsuro
no journal, ,
Radiation energy transfer to extraction solvent in minor actinide separation process were simulated by using a Particle and Heavy Ion Transport code System (PHITS). PHITS enabled to calculate the absorbed dose to extraction solvent in situations of intricately shaped apparatus or oil-water mixed state because the code were based on Monte-Carlo algorithm. It was found that the absorbed dose value from -ray depended on the size of the apparatus, while that from alpha-ray was depended on the droplet size in oil-water mixed state. It was demonstrated the degradation yields of the extractant could be evaluated by reference to the experimentally obtained G-values.
Matsumura, Tatsuro; Ban, Yasutoshi; Hotoku, Shinobu; Suzuki, Hideya; Tsubata, Yasuhiro; Tsutsui, Nao; Morita, Keisuke; Toigawa, Tomohiro; Shibata, Mitsunobu*; Kurosawa, Tatsuya*; et al.
no journal, ,
no abstracts in English
Suzuki, Hideya*; Ban, Yasutoshi; Tsubata, Yasuhiro; Hotoku, Shinobu; Toigawa, Tomohiro; Tsutsui, Nao; Shibata, Mitsunobu*; Kurosawa, Tatsuya*; Kawasaki, Tomohiro*; Matsumura, Tatsuro
no journal, ,
The Japan Atomic Energy Agency has been studying partitioning and transmutation (P&T) systems. In the P&T, the separation of minor actinides (MAs) from the chemically similar lanthanides is the key step. After MAs are separated from high-level waste, the mutual separation of Am and Cm (Am/Cm separation) can be conducted. Therefore, the removal of the pyrogenic Cm nuclide would reduce the difficulties associated with MA-fuel fabrication. However, Am/Cm separation is very challenging because the two elements have similar chemical and physical properties. Highly practical a new reagent, called ADAAM have been developed. The Am is subsequently selectively stripped from the light lanthanides. As a result, Am was separated with high efficiency.
