High Performance Germanium Gamma-Ray Spectrometer on Lunar Polar Orbiter SELENE (KAGUYA)

概要

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The high precision gamma-ray spectrometer (GRS) is carried on the first Japans large-scaled lunar explorer, SELENE (KAGUYA), successfully launched by the H-IIA rocket on Sep. 14, 2007. The GRS consists of a large Ge crystal as a main detector and massive bismuth germanate crystals and a plastic scintillator as anticoincidence detectors. The Ge detector is cooled and kept below 90K by a Stirling cryocooler. After a series of initial health check of the GRS, it started a regular observation on December 21, 2007. Energy spectra of gamma rays are obtained with a good energy resolution over the lunar surface. Energy spectra including many peaks of major elements and trace elements on the lunar surface have been measured by the GRS. The GRS identified individual gamma-ray lines emitted from the lunar surface and provided the global intensity maps of naturally radioactive elements. Here, we review an in-flight performance of the GRS and the initial results observed during the period from Dec. 21, 2007 to Feb. 17, 2008.