Recent outgassing from the lunar surface: The Lunar Prospector Alpha Particle Spectrometer
Recent outgassing from the lunar surface: The Lunar Prospector Alpha Particle Spectrometer
复制标题
最近从月球表面释放的气体：月球勘探者阿尔法粒子光谱仪
DOI：
10.1029/2005je002433
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发表时间：
2005
影响因子：
--
通讯作者：
S. Maurice
中科院分区：
文献类型：
--
作者：
S. Lawson;W. Feldman;D. Lawrence;K. Moore;R. Elphic;R. D. Belian;S. Maurice
[1]月球勘探者阿尔法粒子谱仪（APS）的设计目的是探测Rn-222、Po-218和Po-210衰变产生的特征能量阿尔法粒子，从而绘制月球表面氡释放的位置。这三种核素是铀-238衰变的放射性子体，因此α粒子活动的背景水平是月球地壳铀分布的函数。氡到达月球表面的土壤孔隙率高的地区，或裂缝释放出夹带氡的气体的地方。一旦释放，氡通过随机行走过程中的弹道轨迹在表面上“反弹”而扩散。Rn-222的半衰期允许气体在衰变前扩散数百公里（在月球表面沉积大约一半的Po-218反冲核素），并允许APS在气体释放事件发生后数天内检测气体释放事件。Pb-210前体到Po-210的长停留时间允许绘制在过去大约60年中一直活跃的气体喷口。APS只发现了Po-218 α粒子的微弱迹象。然而，Rn-222 α粒子图显示，在月球勘探者号的时候，氡气是从阿里斯塔斯和开普勒陨石坑附近散发出来的。Po-210 α粒子分布揭示了月球气体释放事件在时间和空间上的变化。Po-210和Rn-222的探测与钍的增强和月球火山碎屑沉积有关。
[1] The Lunar Prospector Alpha Particle Spectrometer (APS) was designed to detect characteristic-energy alpha particles from the decay of Rn-222, Po-218, and Po-210 and to therefore map sites of radon release on the lunar surface. These three nuclides are radioactive daughters from the decay of U-238; hence the background level of alpha particle activity is a function of the lunar crustal uranium distribution. Radon reaches the lunar surface either at areas of high soil porosity or where fissures release the trapped gases in which radon is entrained. Once released, the radon spreads out by “bouncing” across the surface on ballistic trajectories in a random-walk process. The half-life of Rn-222 allows the gas to spread out by several hundred kilometers before it decays (depositing approximately half of the Po-218 recoil nuclides on the lunar surface) and allows the APS to detect gas release events up to several days after they occur. The long residence time of the Pb-210 precursor to Po-210 allows the mapping of gas vents which have been active over the last approximately 60 years. The APS found only a faint indication of Po-218 alpha particles. However, the Rn-222 alpha particle map shows that radon gas was emanating from the vicinity of craters Aristarchus and Kepler at the time of Lunar Prospector. The Po-210 alpha particle distribution reveals a variability in time and space of lunar gas release events. Po-210 and Rn-222 detections are associated with both thorium enhancements and lunar pyroclastic deposits.