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Earth Planets Space, Vol. 60 (No. 4), pp. 299-312, 2008

Gamma-ray spectrometer (GRS) for lunar polar orbiter SELENE

Nobuyuki Hasebe1, Eido Shibamura2, Takashi Miyachi1, Takeshi Takashima3, Masanori Kobayashi4, Osamu Okudaira1, Naoyuki Yamashita1, Shingo Kobayashi1, Takeshi Ishizaki1, Kunitomo Sakurai1, Mitsuhiro Miyajima1, Masayuki Fujii1, Keisuke Narasaki5, Shigeki Takai5, Katsuhiro Tsurumi5, Hiroshi Kaneko6, Michio Nakazawa6, Kunishiro Mori7, Olivier Gasnault8, Sylvestre Maurice8, Claude d'Uston8, Robert C. Reedy9, and Manuel Grande10

1Research Institute for Science and Engineering, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan
2College of Health Science, Saitama Prefectural University, 820, San'nomiya, Koshigaya, Saitama 343-8540, Japan
3Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1, Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan
4Nippon Medical School, 2-297-2, Kosugicho, Nakaharaku, Kawasaki 211-0063, Japan
5Niihama Works, Sumitomo Heavy Industries Ltd., 5-2, soubirakicho, Niihama, Ehime 792-8588, Japan
6Isesaki Works, Meisei Electric Co., Ltd., 2223 Naganumacho, Isesakishi, Gunma 372-8585, Japan
7Clear Pulse Co., Ltd., 6-25-17, Chuo, Ohta-ku, Tokyo 143-0024, Japan 8Centre d'Etude Spatiale des Rayonnements, Univ. Paul Sabatier, CNRS, 9 avenue Roche, 31400 Toulouse, France 9Institute of Meteorites, Univ. of New Mexico, Albuquerque, NM, 87131-1126, USA 10Institute of Mathematical and Physical Sciences, University of Wales, Aberystwyth, Ceredigion SY23 3BZ, Wales, UK

(Received April 1, 2007; Revised December 22, 2007; Accepted December 25, 2007; Online published April 9, 2008)

Abstract: The high-precision gamma-ray spectrometer (GRS) on the lunar polar orbiter SELENE is designed to measure 200 keV-12 MeV gamma rays in order to determine elemental compositions of the lunar surface. The GRS consists of a large germanium (Ge) crystal as a main detector and a massive bismuth germanate crystal and a plastic scintillator as anticoincidence detectors. The Ge detector is cooled by a Stirling cryocooler with its compressor attached to a passive radiator facing the cold space. The cooling system maintains the Ge detector below 90 K during the observation. The flight model of the GRS has achieved an energy resolution of 3.0 keV (FWHM) at 1333 keV. Energy spectra obtained by the GRS will show sharp gamma-ray lines whose energies identify the elements and whose intensities determine the concentrations of the elements, permitting global mapping of the elemental abundances in the sub-surface of the Moon. The elemental maps obtained by the GRS with such high-energy resolution enable us to study lunar geoscience problems.
Key words: Moon, gamma-ray spectroscopy, chemical composition, lunar formation and evolution, SELENE (KAGUYA), GRS.


Corresponding author E-mail: shingo@ruri.waseda.jp


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