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Th as a long-life 
Ac generator using the experimental fast reactor JoyoSasaki, Yuto; Maeda, Shigetaka; Fukasawa, Tetsuo*; Takaki, Naoyuki*
Journal of Nuclear Science and Technology, 63(2), p.154 - 165, 2026/02
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)In recent years, targeted alpha therapy, which utilizes Ac combined with antibodies or peptides that selectively accumulate in cancer cells, has garnered attention in the field of nuclear medicine. To meet the resulting increasing demand for Ac, exploring alternative production methods is essential. While several researchers, including the authors, have explored production methods using 
Ra as a raw material, challenges remain, such as the limited availability of Ra, difficulties in handling it, and the requirement for regular irradiation. To address these challenges, the authors focused on developing a production strategy for a long-life Ac generator using 
Th as a raw material and the experimental fast reactor Joyo. A detailed investigation was conducted, encompassing chemical processing after irradiation, target availability, and production yields, including the most probable values and associated uncertainties. Results revealed that although enrichment of the raw material and long-term irradiation are required, Ac can be produced in quantities comparable to its current global supply. Furthermore, this research has shown that the THOREX method, which is already in practical use, be applied to effectively separate by-products such as fission products and radioactive materials from thorium during the chemical processing after irradiation, as revealed by a literature survey.
Kato, Yuto*; Sasaki, Takayuki*; Tonna, Ryutaro*; Kobayashi, Taishi*; Okamoto, Yoshihiro
Applied Geochemistry, 175, p.106196_1 - 106196_9, 2024/11
Times Cited Count：3 Percentile：39.78(Geochemistry & Geophysics)Nakata, Yuto; Sasaki, Takehiko*; Thomsen, B.; Shiga, Motoyuki
Chemical Physics Letters, 845, p.141285_1 - 141285_9, 2024/06
Times Cited Count：0 Percentile：0.00(Chemistry, Physical)Using density functional theory and metadynamics simulations, we study cellobiose hydrolysis and glucose hydrogenation with silica-supported platinum and palladium catalysts in hot water, relevant to green cellulose conversion. It is found that cellobiose hydrolysis can proceed by the attack of hydrogen atoms adsorbed on metal or protons spilled over to silica forming glucose. Glucose can then be hydrogenated by hydrogen atoms adsorbed at platinum/water interface forming sorbitol. The reaction barriers of hydrolysis and hydrogenation at platinum/water interface are both lower than that at palladium/water interface, which explains the experimental finding that the platinum performs as a better catalyst than palladium.
Ac and its uncertainty through the Ra(n,2n) reaction in the experimental fast reactor JoyoSasaki, Yuto*; Sano, Aaru; Sasaki, Shinji; Iwamoto, Nobuyuki; Ouchi, Kazuki; Kitatsuji, Yoshihiro; Takaki, Naoyuki*; Maeda, Shigetaka
Journal of Nuclear Science and Technology, 61(4), p.509 - 520, 2024/04
Times Cited Count：9 Percentile：84.77(Nuclear Science & Technology)Ac is attracting attention as an alpha-emitting medical radioisotope. Since its demand is expected to increase, domestic production of Ac is required from the viewpoint of Japan's medical research and economic security. To establish the technical bases for the Ac production, JAEA has evaluated the radioactivity that can be produced in the experimental fast reactor Joyo and designed the concept that upgrades the existing facilities for transporting the irradiated target from Joyo to a neighboring PIE facility rapidly. Efficient Ac Separation from Ra irradiated in a fast reactor was studied. Ba and La were used as alternatives to Ra and Ac, respectively. By using DGA resin as an adsorbent, it can be expected that Ra and impurities generated by irradiation will be removed and Ac will be isolated. This study has revealed that Joyo can sufficiently produce Ac as a raw material for pharmaceuticals.
Ra nuclear data library and its impact on the production amount of Ac via the Ra (n,2n) reactionSasaki, Yuto; Iwamoto, Nobuyuki; Takaki, Naoyuki*; Maeda, Shigetaka
Journal of Nuclear Science and Technology, 61(2), p.251 - 260, 2024/02
Times Cited Count：1 Percentile：30.56(Nuclear Science & Technology)Ac is a promising alpha emitter for targeted alpha therapy. However, the current capability of Ac supply is limited to approximately 63 GBq/y, primarily relying on the natural source of Th stocked at a few institutes. Therefore, alternative Ac production methods are highly desired. The research and development of Ac and its parent nuclide production methods using accelerators and reactors to target Ra and 
Th are actively pursued worldwide. Hence, the authors focused on the Ra(n,2n) Ra method using fast neutron spectra as an application of the experimental fast reactor Joyo. This study investigated the status of nuclear data libraries for Ra, an essential target for Ac production, and evaluated the impact of different nuclear data libraries on the amount of Ac produced. Consequently, cross-sections with covariance data were stored in TENDL-2021, JEFF-3.3, and EAF-2010 but not in ENDF or JENDL, the major nuclear data libraries. Furthermore, no consistency occurred among the respective nuclear data, and the Ra production amount varied.
Ra purity as a target for Ac production using a fast reactorSasaki, Yuto; Maeda, Shigetaka
Journal of Radioanalytical and Nuclear Chemistry, 333, p.5987 - 5996, 2024/02
Times Cited Count：1 Percentile：30.56(Chemistry, Analytical)Researchers are seeking alternative Ac production methods because of the scarcity of Ac for targeted alpha therapy. Although Ra from waste sources has been considered, obtaining Ra is challenging. Therefore, the authors focused on the contamination of minerals with Th-derived 
Ra while investigating methods to recover Ra from uranium ores. The effect of 228Ra contamination on Ac production by Ra transmutation using fast reactors was evaluated. Consequently, toxic Ac contaminates Ac. However, using the different half-lives of Ac and Ac, pure Ac can be obtained from the chemical separation of actinium after cooling for 5-8 days.
Yoshida, Masafumi; Hanada, Masaya; Kojima, Atsushi; Kashiwagi, Mieko; Grisham, L. R.*; Hatayama, Akiyoshi*; Shibata, Takanori*; Yamamoto, Takashi*; Akino, Noboru; Endo, Yasuei; et al.
Fusion Engineering and Design, 96-97, p.616 - 619, 2015/10
Times Cited Count：14 Percentile：68.19(Nuclear Science & Technology)In JT-60 Super Advanced for the fusion experiment, 22A, 100s negative ions are designed to be extracted from the world largest ion extraction area of 450 mm 
1100 mm. One of the key issues for producing such as high current beams is to improve non-uniform production of the negative ions. In order to improve the uniformity of the negative ions, a tent-shaped magnetic filter has newly been developed and tested for JT-60SA negative ion source. The original tent-shaped filter significantly improved the logitudunal uniformity of the extracted H
ion beams. The logitudinal uniform areas within a 
10 deviation of the beam intensity were improved from 45% to 70% of the ion extraction area. However, this improvement degrades a horizontal uniformity. For this, the uniform areas was no more than 55% of the total ion extraction area. In order to improve the horizontal uniformity, the filter strength has been reduced from 660 Gasus
cm to 400 Gasuscm. This reduction improved the horizontal uniform area from 75% to 90% without degrading the logitudinal uniformity. This resulted in the improvement of the uniform area from 45% of the total ion extraction areas. This improvement of the uniform area leads to the production of a 22A H ion beam from 450 mm 1100 mm with a small amount increase of electron current of 10%. The obtained beam current fulfills the requirement for JT-60SA.
Yoshida, Masafumi; Hanada, Masaya; Kojima, Atsushi; Kashiwagi, Mieko; Grisham, L. R.*; Akino, Noboru; Endo, Yasuei; Komata, Masao; Mogaki, Kazuhiko; Nemoto, Shuji; et al.
Review of Scientific Instruments, 85(2), p.02B314_1 - 02B314_4, 2014/02
Times Cited Count：16 Percentile：53.56(Instruments & Instrumentation)Non-uniformity of the negative ion beams in the JT-60 negative ion source was improved by modifying an external magnetic field to a tent-shaped magnetic field for reduction of the local heat loads in the source. Distributions of the source plasmas (H
ions and H
atoms) of the parents of H ions converted on the cesium covered plasma grids were measured by Langmuir probes and emission spectroscopy. Beam intensities of the H ions extracted from the plasma grids were measured by IR camera from the back of the beam target plate. The tent-shaped magnetic field prevented the source plasmas to be localized by B grad B drift of the primary electrons emitted from the filaments in the arc chamber. As a result, standard derivation of the H ions beams was reduced from 14% (the external magnetic field) to 10% (the tent-shaped magnetic field) without reduction of an activity of the H ion production.
Yoshida, Masafumi; Hanada, Masaya; Kojima, Atsushi; Inoue, Takashi; Kashiwagi, Mieko; Grisham, L. R.*; Akino, Noboru; Endo, Yasuei; Komata, Masao; Mogaki, Kazuhiko; et al.
Plasma and Fusion Research (Internet), 8(Sp.1), p.2405146_1 - 2405146_4, 2013/11
Distributions of H and H in the source plasmas produced at the end-plugs of JT-60 negative ions source were measured by Langmuir probes and emission spectroscopy in order to experimentally investigate the cause of lower density of the negative ions extracted from end-plugs in the source. Densities of H and H in end-plugs of the plasma grid in the source were compared with those in the center regions. As a result, lower density of the negative ion at the edge was caused by lower beam optics due to lower and higher density of the H and H.
Motokawa, Ryuhei; Taniguchi, Tatsuo*; Sasaki, Yusuke*; Enomoto, Yuto*; Murakami, Fumiyasu*; Kasuya, Masakatsu*; Kori, Michinari*; Nakahira, Takayuki*
Macromolecules, 45(23), p.9435 - 9444, 2012/11
Times Cited Count：10 Percentile：30.74(Polymer Science)Ac production rate and its uncertainty in the experimental fast reactor Joyo utilizing the total Monte Carlo methodSasaki, Yuto; Iwahashi, Daiki*; Maeda, Shigetaka; Takaki, Naoyuki*
no journal, ,
Ac-225 is attracting attention as an alpha emitting medical radioisotope. Since its demand is expected to increase, domestic production of Ac-225 is required from the viewpoint of medical research and economic security of Japan. To establish the technical bases for the Ac-225 production, JAEA has evaluated the radioactivity can be produced in the experimental fast reactor Joyo and designed the concept that upgrades the existing facilities for transporting the irradiated target from Joyo to a neighboring PIE facility rapidly. This study has revealed that Joyo can sufficiently produce Ac-225 as a raw material for pharmaceuticals.
Sasaki, Yuto
no journal, ,
no abstracts in English
Sasaki, Yuto; Iwamoto, Nobuyuki; Maeda, Shigetaka; Takaki, Naoyuki*
no journal, ,
In Japan, research is being promoted to improve and achieve domestic preparedness for the production of medical radioisotopes (RI) using existing fission reactors. We investigated the efficient production of 
Mo/
Tc by neutron activation with an alternative method of producing Mo that does not use enriched uranium (HEU, LEU) as a raw material, utilizing the neutron moderator filed around the core of the experimental fast reactor Joyo. As a result, we found that 23133 TBq of Mo can be produced by irradiating the sample for 7 days in an irradiation field using a moderated assembly with a beryllium filling rate of 60%. This amount is enough to meet domestic weekly demand, even if we consider a supply of once every two weeks. However, Joyo has difficulty in continuing production due to annual inspections. Therefore, it would be possible to achieve a stable supply by establishing a supply system that is a best mix of other research reactors and accelerators.
Sasaki, Yuto; Okagaki, Masaki; Maeda, Shigetaka
no journal, ,
The experimental fast reactor Joyo is the only fast neutron spectrum reactor in the OECD member countries. It has been used for demonstration tests of the safety features unique to fast reactors, such as fuel breeding and core cooling by natural circulation of sodium cooling. Currently, work is underway to comply with the new regulatory standards, and it is scheduled to be restarted in JFY2026. After restarting, it is planned to be used for a variety of purposes, such as the development of fast demonstration reactors, irradiation of materials such as fusion materials, and the production of radioactive isotopes for medical use. In particular, the production of medical radioisotopes can be carried out not only using methods that make the most of the fast neutron spectrum unique to fast reactors, such as the (n,2n) reaction necessary for the production of Ac, but also by adjusting the neutron spectrum flexibly using various moderators, making it possible to carry out irradiation in a thermal neutron spectrum environment, such as the (n,
) reaction necessary for the production of Mo. At this conference, we will report on the technology for producing medical radioisotopes using the experimental fast reactor Joyo.
Sasaki, Yuto; Maeda, Shigetaka
no journal, ,
Targeted alpha particle therapy is gaining attention in the field of nuclear medicine. This treatment combines short-lived alpha-emitting radionuclides with antibodies or peptides that selectively accumulate in cancer cells. In 2016, the therapeutic efficacy of Actinium-225 (Ac-225) as an alpha-emitting radionuclide for prostate cancer was reported, and its potential application to other cancers is also currently under investigation. As a result, the demand for Ac-225 is rapidly increasing in the world. Internationally, production methods such as generator-based and accelerator-based approaches are being developed. In Japan, domestic production using nuclear reactors and accelerators is being promoted under the Medical and Other Radioisotope Production and Utilization Promotion Action Plan of the Atomic Energy Commission. The fast experimental reactor Joyo, owned by JAEA, holds promise for large-scale production, with plans to demonstrate production by the JFY2026. This symposium will present the principles of Ac-225 production, the details of the demonstration plan, and future prospects for meeting domestic demand. It will also address the required quality specifications for the target nuclide, particularly the ratio of Ra-226 to Ra-228. Ra-226 is a key target in Ac-225 production via both accelerator and reactor methods, and its purity is critical to ensuring the efficiency and safety of the production process.
Aratani, Kenta; Matsushima, Akira; Takiya, Hiroaki; Awatani, Yuto; Sasaki, Katsuya*; Maehata, Hidehiko*; Maruyama, Akira*
no journal, ,
no abstracts in English
Sano, Aaru; Sasaki, Yuto*; Sasaki, Shinji; Iwamoto, Nobuyuki; Ouchi, Kazuki; Kitatsuji, Yoshihiro; Maeda, Shigetaka; Takaki, Naoyuki*
no journal, ,
Ac-225 can be applied to cancer treatment of various sites, but world supply is scarce. In this study, in order to study the production of Ac-225 using fast neutrons, we evaluated the amount of Ac-225 produced by fast neutron irradiation of Joyo. Burn up calculations were performed with Ra-226 as the target using ORIGEN2.2 for the evaluation of the production amount. In addition, the uncertainty of Ac-225 production was evaluated from the nuclear reaction cross section of the target nuclide and the neutron flux of Joyo. This study showed that a large amount of Ac-225 can be produced by irradiating Ra-226 at Joyo. In the future, we will improve the accuracy of evaluation of the production amount through demonstration experiments.
Takaki, Naoyuki*; Iwahashi, Daiki*; Sasaki, Yuto*; Maeda, Shigetaka
no journal, ,
The production technology of medical radioisotopes (RI) using existing nuclear fission reactors has been studied to improve/achieve their domestic preparedness in Japan. The target nuclides currently considered in our project are Mo/Tc which is the most commonly used ones in medical diagnosis and Ac-225 which is recently known as effective alpha emitting nuclide for targeted alpha-particle therapy. Existing fission reactors, PWRs and Joyo, have potentials to work as excellent facilities for medical isotope production, as by-products of heat/electricity generation without consuming electricity and need for new plant construction.
Sasaki, Yuto; Sano, Aaru; Itagaki, Wataru; Maeda, Shigetaka; Takaki, Naoyuki*
no journal, ,
no abstracts in English
