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Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke; Hirata, Yuho; Tezuka, Tomoya*; Tsuchida, Hidetsugu*; Yokoya, Akinari*
RSC Advances (Internet), 13(46), p.32371 - 32380, 2023/11
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
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：1 Percentile：67.19(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：9 Percentile：74.41(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：11.21(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：19 Percentile：73.52(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.
Kai, Takeshi; Yokoya, Akinari*; Ukai, Masatoshi*; Fujii, Kentaro*; Watanabe, Ritsuko*; Yonetani, Yoshiteru*; Toigawa, Tomohiro; Sato, Tatsuhiko
no journal, ,
It is very important to study water radiolysis by electrons because the study are applied to fields involved in atomic industry and radiotherapy, the study is also useful to predict radiation damage to DNA in a living cell. In this study, we calculated deceleration process of secondary electrons produced by ionization at a primary electron track end, at which a primary and secondary electrons densely deposit those energies to water, to understand the earliest process of water radiolysis. From the results, the secondary electrons distributed 10 nm from parent cations at 300 fs, and the mean energy of the electrons reached 0.7 eV. At this timescale, we indicated that the energy distribution shows the non-equilibrium state strongly, and fraction of the electrons energy below 0.1 eV is more than 10
. The results may indicate a new insight of the formation of prehydrated electrons due to the extremely low energy electrons.
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.
Matsumura, Tatsuro; Ban, Yasutoshi; Suzuki, Hideya; Tsubata, Yasuhiro; Toigawa, Tomohiro; Tsutsui, Nao; Hotoku, Shinobu; Suzuki, Asuka
no journal, ,
no abstracts in English
Toigawa, Tomohiro; Suzuki, Hideya; Ban, Yasutoshi; Ishii, Sho; Matsumura, Tatsuro
no journal, ,
Degradation of extractants and generation of radiolytic products are considered as problem for feasibility of the minor actinides separation process. In this study, degradation amount of hexaoctyl-nitrilotriacetamide (HONTA), which is a candidate extaractant for MA/Ln separation, and its products yields were obtained by using 
-rays emitted from Co-60. Our results showed the cleavage sites in HONTA radiolysis and suggest that the mechanism for HONTA radiolysis is differ depending on the absorbed dose.
Toigawa, Tomohiro; Suzuki, Hideya; Ban, Yasutoshi; Ishii, Sho*; Matsumura, Tatsuro
no journal, ,
R&D on partitioning process of the minor actinides (MA) from high level liquid waste (HLLW) were carried out for reduction of the strain on the radioactive wastes disposal. In this study, degradation amount of hexaoctyl-nitrilotriacetamide (HONTA), which is a candidate extaractant for MA/RE separation, and its products yields were obtained by using -rays emitted from Co-60. Our results showed the cleavage sites in HONTA radiolysis and suggest that the mechanism for HONTA radiolysis is differ depending on the absorbed dose.
and Cm using a high-performance ligandSuzuki, Hideya; Tsubata, Yasuhiro; Toigawa, Tomohiro; Matsumura, Tatsuro
no journal, ,
The separation of minor actinide (MA) from HLLW is an important task in the partitioning and transmutation. After MA are separated from HLLW, the mutual separation of Am and Cm (Am/Cm separation) can be conducted. A highly practical reagent, called alkyl diamide amine (ADAAM), was developed. ADAAM gives the maximum separation factor up to 5.5. A continuous extraction test was conducted using a multistage countercurrent mixer-settler extractor with ADAAM in n-dodecane. Separation of Am and Cm was demonstrated in very high yield.
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.
Matsumura, Tatsuro; Ban, Yasutoshi; Suzuki, Hideya; Tsubata, Yasuhiro; Hotoku, Shinobu; Tsutsui, Nao; Suzuki, Asuka; Toigawa, Tomohiro; Kurosawa, Tatsuya*; Shibata, Mitsunobu*; et al.
no journal, ,
To continue the utilization of the nuclear fission energy, the management of the high-level radioactive waste is one of the most important issues to be solved. Partitioning and Transmutation technology is expected to be effective to mitigate the burden of the HLW disposal by reducing the radiological toxicity and heat generation. JAEA has been conducting R&D on the MA separation process to remove of MA from HLW and supply the recovered MA to the transmutation system such as ADS. The MA separation process contains three steps. For An(III)+RE recovery process, we developed TDdDGA which has very high performance to recover of MA from high level waste. HONTA and ADAAM were developed for An(III)/RE separation process and Am/Cm separation process respectively. All extractants satisfy CHON principle to minimization of the secondary waste from the process. The separation performances of the flowsheets were evaluated by continuous extraction tests using simulated and genuine high level liquid waste.
Matsumura, Tatsuro; Ban, Yasutoshi; Suzuki, Hideya; Tsubata, Yasuhiro; Hotoku, Shinobu; Tsutsui, Nao; Suzuki, Asuka; Toigawa, Tomohiro; Kurosawa, Tatsuya*; Shibata, Mitsunobu*; et al.
no journal, ,
PUREX process was established for industrial scale reprocessing plant. TRUEX and the 4 group separation were developed for partitioning of minor actinides from HLW, and demonstrated using genuine HLW. Although the extractants for the processes have excellent performance, the molecules contain phosphorus which could be cause for the secondary waste from the solvent extraction processes. To minimize the radioactive waste, we have conducted research and development of the new reprocessing and MA separation processes using innovative extractants in accord with CHON principle. The extractants for reprocessing process are monoamides as alternative extractants for TBP. For An(III)+RE recovery process, we developed TDdDGA. HONTA and ADAAM were developed for An(III)/RE separation process and Am/Cm separation process respectively. The separation performances of the flowsheets were evaluated by continuous extraction tests using simulated and genuine spent fuel and high level liquid waste.
Kai, Takeshi; Toigawa, Tomohiro; Ukai, Masatoshi*; Fujii, Kentaro*; Watanabe, Ritsuko*; Yokoya, Akinari*
no journal, ,
Fundamental studies of water radiolysis by radiation and laser irradiation are applied to atomic industry, and provide useful fundamental insights to understanding of radiation DNA damage. We developed a code to simulate dynamic behavior of electrons produced in water by energy deposition at energies, also performed theoretical study for the behaviors. The spatial probability distributions of the electrons depend on the deposition energies, also show the exponential or Gaussian types. We also show calculated results of energy probability distributions of the electrons. We found that the distributions below 100 meV are gradually close to Maxwell distribution with the temporal evolution, while the distributions above 100 meV not depend on the temporal evolution due to effect of Coulombic field of the parent cation. The findings provide significant insights to a connection radiation physics and radiation chemistry.
Toigawa, Tomohiro; Tsubata, Yasuhiro; Kai, Takeshi; Kimura, Takahiro; Ban, Yasutoshi; Suzuki, Hideya; Tsutsui, Nao; Hotoku, Shinobu; Matsumura, Tatsuro
no journal, ,
To evaluate the radiation Stability of the extraction agent applied to the solvent extraction process, energy transfer process to extraction solvent was 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 extractant could be evaluated by reference to the experimentally obtained G-values.
-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.
