オクノ ショウジ   Okuno Shoji
  奥野 祥二
   所属   神奈川大学  工学部 情報システム創成学科
   職種   助教
言語種別 日本語
発行・発表の年月 2006/05
形態種別 学術雑誌
査読 査読あり
標題 Radon alpha-ray detector on-board lunar mission SELENE
執筆形態 共著
掲載誌名 Advances in Space Research
巻・号・頁 37(1),34-37頁
著者・共著者 J. Nishimura, T. Kashiwagi, T. Takashima, S. Okuno, K. Yoshida, K. Mori, M. Itoh, K. Saeki and K. Furuichi
概要 Alpha-ray detector (ARD) will be on-board SELENE, a Japanese lunar orbiter to be launched around 2006. Primary target is the alpha particles emitted by 222Rn and 210Po. 222Rn is produced by the decay of 238U and emanates from the lunar surface. It is trapped by the lunar gravity and decays with the half-life of 3.8 days emitting 5.490 MeV alpha particle. In the decay sequence of 222Rn, 210Po emits alpha particle with the energy of 5.305 MeV. Time scale of the activity is dominated by the 21-year half-life of 210Pb. Thus, alpha particle intensity from 210Po is an indicator of the change of radon emanation rate and change of crust condition due to seismic activity or impact events for the time scale of not, vert, §im50 years, while that of 222Rn reflects the current emanation rate. Results from Apollo 15, 16, and recent Lunar Prospector mission indicate that the average amount of radon on the lunar surface is much smaller than expected, and the radon-alpha distribution suggests that radon comes out through gas emanation from fissures of the lunar surface. We developed a large-area detector of 326 cm2 for the ARD, which is 15-20 times larger than the detectors of Apollo and Lunar Prospector. Reduction of the background was achieved with the anti-coincidence by rejecting cosmic-ray tracks. It will enable: (1) precise global mapping of the radioactive material on the lunar surface; (2) identification of gas emanation location; (3) study of the radon gas emanation mechanism on the lunar surface and the origin of the lunar atmosphere; (4) obtaining information on the crustal movement during the last not, vert, §im50 years.