Chang’E-1 gamma ray spectrometer and preliminary radioactive results on the lunar surface

The Chang’E-1(CE-1) spacecraft took a gamma-ray spectrometer (hereafter, CGRS) to detect the element distributions on the lunar surface in a circular, 200 km altitude, polar orbit with approximately 2 h periodicity. CGRS consists of two large CsI(Tl) crystals as the main and anticoincidence detectors. The large CsI crystal of CGRS has a higher detector effective area than other lunar gamma ray spectrometers. For its 1-year mission, gamma ray spectra including many peaks of major elements and trace elements on the lunar surface have been measured by CGRS. Global measurement within 0.55-0.75 MeV is given here to describe the distribution of radioactive composition (e.g., uranium and thorium) on the lunar surface. Although CGRS has a lower energy resolution that cannot separate the uranium peak from others in this energy region, 609 keV uranium gamma ray line dominates the shape of the spectrum in this energy region. Therefore, the radioactive map can indirectly describe the uranium distribution on the lunar surface. The radioactive map shows that the higher radiation is concentrated in the Procellarum KREEP Terrene (PKT) on the nearside with an oval shape. The secondary high-radiation is located in South Pole-Aitken (SPA) basin. Lunar highlands have lower concentration. The relationship between radiation and topography displays different linear correlations for lunar highlands and SPA basin, which imply the different processes for these two regions.     

双地下物质变化区参数解算方法研究

经典天体测量仪器以铅垂线为基准测量本地的天文经纬度,因而能探测到本地铅垂线的偏转.本地铅垂线的偏转代表着测站周围重力场的变化,而这一变化与地下物质的再分布相关,由此有望帮助了解地下物质变化的情况.将本地的铅垂线偏转(Plumb Line Variation, PLV)与地下物质变化联系起来,建立了双质量体模型.在97°E–107°E和21°N–29°N范围内,考虑了3480个包含正、负质量变化(相对地质背景)的质量体组合算例,并利用差分进化(Differential Evolutionary, DE)算法进行了解算.解算得到的质量体相对于模拟值的位置误差小于米量级,质量误差小于10¹¹kg,结果精度较高.