陨石中宇宙成因核素^(10)Be和^(26)Al的化学分离纯化  

Chemical separation and purification of cosmogenic radionuclides ^(10)Be and ^(26)Al in meteorites

作　　者：卢仁[1] 林杨挺[2] 欧阳自远[1] 李春来[3] 周卫健[4] 

机构地区：[1]中国科学院地球化学研究所,贵州贵阳550002 [2]中国科学院地质与地球物理研究所,北京100029 [3]中国科学院国家天文台,北京100012 [4]中国科学院地球环境研究所西安加速器质谱中心,陕西西安710075

出　　处：《地球化学》2008年第2期149-156,共8页Geochimica

基　　金：中国科学院知识创新工程重要方向项目(KZCX2-YW-110)

摘　　要：陨石离开其小行星母体直至降到地球表面期间,受到宇宙射线的照射,产生一系列包括10Be和26Al等的放射性核素。10Be和26Al的含量及其比值记录了宇宙射线辐照历史,而陨石降落到地球表面后,它们的衰变又提供了测定其降落时间,即居地年龄的方法。10Be和26Al由加速器质谱测定,样品需分离纯化。为此,开展了陨石样品Be和Al的分离纯化实验。通过模拟样品的条件实验,建立了Be和Al分离纯化的化学流程,其回收率分别达到89%和70%。在此基础上,分离并测定了一个降落型普通球粒陨石(吉林陨石)非磁性部分的10Be和26Al的含量。结果显示,吉林陨石26Al/10Be的比值为5.005,远大于两者的饱和比值(2.72),说明吉林陨石经历了短期的暴露辐射,这一结果与吉林陨石第二阶段的暴露年龄0.4Ma一致。整个化学流程的10Be/9Be和26Al/27Al空白分别为(4.33±0.46)×10-14和(6.59±4.66)×10-15,其中前者接近于该仪器的空白测量值,而后者则接近于仪器的检测限2.3×10-15。Meteorites were irradiated by cosmic rays after being ejected from their parent asteroids until falling on the Earth, producing various radionuclides, including 10↑Be and 26↑Al. The concentrations of 10↑Be and 26↑Al and their ratios are related with their cosmic-ray exposure histories. After falling onto the Earth, the meteorites were shielded by atmosphere from cosmic-ray irradiation, and their concentrations of 10↑Be and 26↑Al are decreasing due to decay. Hence, it is possible to determine when the meteorites fell, namely the terrestrial ages. 10↑Be and 26↑Al were measured by accelerator mass spectrometry （AMS）. Before instrumental measurement, a modified chemical procedure of separating and purifying Be and Al from meteorites was developed. 89% of Al and 70% of Be can be recovered after the separation. Our analysis of a fall meteorite, the Jilin （H5） chondrite, shows a 26↑Al/10↑Be ratio of 5.005, much higher than the saturation ratio （2. 72） of H chondrites, indicating a rather short cosmic-ray exposure in comparison with the half-lives of 10↑Be and 26↑Al. This is in agreement with the exposure age of 0. 4 Ma of the second irradiation stage of Jilin chondrite. The ratios of 10↑Be/9↑Be and 26↑Al/27↑Al in blank of the whole chemical procedure are （4.33 ±0. 46） × 10^-14 and （6. 59 ±4.66） × 10^-15, respectively. The former is close to the instrumental blank and the latter is comparable to the instrumental detection limit of 2. 3 × 10^-15.

关 键 词：陨石 宇宙成因放射性核素 10↑Be和26↑Al 化学分离纯化 居地年龄 

分 类 号：P597[天文地球—地球化学] P148[天文地球—地质学]