An Experimental Attempt to Determine History of 3He, 4He, and Isotopes of Ne and Ar in the Mantle

该项目将确定He、Ne和Ar同位素的历史 根据对钻石和相关地幔的研究， 样品 当这项研究进行时，一些人认为， 某些钻石记录了原始氦同位素 混合物. 钻石似乎不太可能 地球起源时He成分的残留记录; 可能具有高3 He/4 He比率的钻石获得了它们的3 He 在宇宙射线的作用下， 相互作用，或通过放射性中子与 如果锂在金刚石中的浓度超过1 ppm. 冲积金刚石中宇宙成因~ 3 He组分的发现 观察非常大的氦在钻石中的扩散率， 非常奇怪的释放模式，以及其他紧急观察 保证氦研究的扩展，包括Ne（和Ar） 同位素 Ne的同位素组成可能确实具有 与古老钻石的形成有关 此外，还计划确定宇宙射线暴露的历史， 用~（21）Ne和~（10）Be作示踪剂的冲积金刚石。 实验室准备好了 用于3 He测量;低空白系统是在 之前的NSF资助。 氖同位素测量现在可以 以所需的精度进行，因为同位素 实验室将很快获得一个三重收集器N2-Ne质量 在NSF的资助下，

This project will determine the history of He, Ne and Ar isotopes in the mantle, based on studies of diamonds and associated mantle samples. When this study was undertaken, it was believed by some that certain diamonds bore records of pristine helium isotopic composition. It is how seems unlikely that diamonds could carry vestigial records of He composition at genesis of the Earth; most likely diamonds having high 3He/4He ratios acquired their3He during their residence in the alluvium by cosmic ray interactions, or by interactions of radiogenic neutrons with lithium if present in the diamond at concentrations exceeding 1 ppm. Discovery of the cosmogenic 3He component in alluvial diamonds, observations of very large helium diffusivity in diamonds, with a very strange release pattern, and other observations urgently warrant extension of helium studies, including Ne (and Ar) isotopes. The isotopic composition of Ne may indeed have a bearing on the formation of old diamonds. Also it is planned to determine cosmic ray exposure histories of alluvial diamonds using 21Ne and 10Be as tracers. The lab is set up for 3He measurements; low blank systems were built under the previous NSF grant. Neon isotopic measurements can now be carried out with the required precision since the Isotope Laboratory will soon be acquiring a triple collector N2-Ne mass spectrometer under a grant from NSF.