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Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

 Times Cited Count:30 Percentile:96.87(Astronomy & Astrophysics)

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Oral presentation

Nuclear and radiochemical study of production and utilization of radioactive astatine isotopes using lithium ion beams at the tandem accelerator of JAEA-Tokai

Nishinaka, Ichiro; Yokoyama, Akihiko*; Washiyama, Koshin*; Amano, Ryohei*; Yamada, Norihiro*; Ishiguro, Rika*; Makii, Hiroyuki; Hashimoto, Kazuyuki

no journal, , 

An $$alpha$$ radioactive nuclide $$^{211}$$At is a prospective candidate for utilization in targeted alpha radiotherapy. We have started nuclear and radiochemical study of production and utilization of radioactive astatine isotopes using lithium ion beams at the tandem accelerator of JAEA-Tokai. We determined the excitation functions of astatine isotopes in the reaction of 29-48 MeV $$^7$$Li+$$^{nat}$$Pb and studied a chemical behavior of carrier-free radioactive astatine isotopes with a dry-chemistry method. Details will be shown in the presentation.

Oral presentation

Production of astatine radioisotopes in the $$^7$$Li+$$^{nat}$$Pb reaction and simple chemical separation of astatine

Nishinaka, Ichiro; Yokoyama, Akihiko*; Washiyama, Koshin*; Amano, Ryohei*; Ri, Keiko*; Yamada, Norihiro*; Ishiguro, Rika*; Maeda, Eita*; Makii, Hiroyuki; Hashimoto, Kazuyuki; et al.

no journal, , 

We have started to study production and utilization of an $$alpha$$ radioactive nuclide $$^{211}$$At which is a prospective candidate for targeted alpha radiotherapy. We determined production cross sections of astatine radioisotopes in the reaction of 29-48 MeV $$^7$$Li+$$^{nat}$$Pb by $$alpha$$-ray and $$gamma$$-ray spectrometry at the tandem accelerator of JAEA-Tokai. Besides, we developed a simple dry-chemical method for separation of astatine.

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