Isotopic compositions of rare gases in the carbonaceous chondrites Mokoia and Allende
Isotopic compositions of rare gases in the carbonaceous chondrites Mokoia and Allende
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碳质球粒陨石莫科亚和阿连德中稀有气体的同位素组成
DOI：
10.1016/0016-7037(72)90016-6
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发表时间：
1972
影响因子：
5
通讯作者：
P. K. Kuroda
中科院分区：
文献类型：
--
作者：
O. Manuel;R. Wright;D. K. Miller;P. K. Kuroda
用质谱仪测定了碳质球粒陨石Mokoia和Allende在分步加热实验中释放出的Ne、Ar、氪和Xe的同位素组成。不同温度下陨石释放出的稀有气体的同位素组成差异很大。例如，观测到的最小值和最大值如下：Ne 20Ne 22=2.1(阿连德800°C)和12.95(莫科亚400°C)；Ar 36 Ar 38=4.2(阿连德1600°C)和6.05(阿连德800°C)；Kr 84 Kr 86=3.140(阿连德1000°C)和3.306(莫科亚600°C)；Xe 134Xe136=1.019(阿连德800°C)和1.192(阿连德1400°C)。在这两块陨石中都观察到了由于已灭绝的核素I126的衰变而显着地浓缩了Xe 129。同位素比率的变化部分是由宇宙线散裂和中子俘获产物的存在引起的。然而，此外，在这项工作中观察到了同位素比率随质量变化的显著趋势。陨石释放的稀有气体同位素似乎相对于平均碳质球粒陨石(AVCC)的相对丰度有系统的质量分馏。似乎可以很好地解释这一现象，因为在陨石中存在两个同位素不同的气体储存库，并且这些气体的混合物在每个温度分数下被释放。这里考虑的两种不同气体最有可能是所谓的太阳稀有气体和行星稀有气体，它们的同位素组成截然不同。
The isotopic compositions have been measured mass spectrometrically for neon, argon, krypton and xenon released from the carbonaceous chondrites Mokoia and Allende in stepwise heating experiments. The isotopic compositions of rare gases released from the meteorites at different temperatures varied quite considerably. The observed minimum and maximum values were, for example, as follows: Ne 20 Ne 22= 2.10 (Allende 800° C) and 12.95 (Mokoia 400° C); Ar 36 Ar 38= 4.20 (Allende 1600° C) and 6.05 (Allende 800° C); Kr 84 Kr 86= 3.140 (Allende 1000° C) and 3.306 (Mokoia 600° C); Xe 134 Xe 136= 1.019 (Allende 800° C) and 1.192 (Allende 1400° C). A marked enrichment of Xe 129 due to the decay of extinct nuclide I 126 was observed in both meteorites. The variations of the isotopic ratios are partly caused by the presence of cosmic-ray spallation and neutron-capture products. In addition, however, a marked trend of mass-dependent variation of the isotopic ratios was observed in this work. The rare gas isotopes released from the meteorites appear to be systematically mass-fractionated relative to the relative abundances of the average carbonaceous chondrite (AVCC). It seems that this phenomenon can be best explained as due to the fact that there exist reservoirs of two isotopically distinct gases in the meteorites and mixtures of these gases are being released at each temperature fraction. The two different gases being considered here are most likely the so-called solar and planetary rare gases, whose isotopic compositions are quite different from each other.