The record of cosmogenic, radiogenic, fissiogenic, and trapped noble gases in recently recovered Chinese and other chondrites
The record of cosmogenic, radiogenic, fissiogenic, and trapped noble gases in recently recovered Chinese and other chondrites
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最近回收的中国球粒陨石和其他球粒陨石中宇宙成因、放射成因、裂变和捕获的稀有气体的记录
DOI：
10.1016/0016-7037(93)90045-x
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发表时间：
1993
影响因子：
5
通讯作者：
W. Yi
中科院分区：
文献类型：
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作者：
O. Eugster;T. Michel;S. Niedermann;Ding;W. Yi
我们对36颗球粒陨石进行了稀有气体同位素丰度的综合研究，其中中国回收了27颗球粒陨石。庞大的数据库使我们认识到球粒物质核记录的一些新特征。普通球粒陨石和碳质球粒陨石捕获稀有气体释放模式的比较表明，普通球粒陨石中行星捕获稀有气体主要在1200℃以上释放，而碳质球粒陨石中≥85%的气体在≥200℃时脱气。由此看来，在普通球粒陨石和碳质球粒陨石中捕获的稀有气体的载流子相可能不相同。Ngawi LL3球粒陨石富含太阳能气体。陨石和月球表面物质中的太阳气体是太阳风（SW）和太阳高能粒子（SEP）的混合物。我们发现富太阳气体陨石和月球表面物质的3 He 4 He和20 Ne 22 Ne比值的变化可能是由于He和Ne的较轻同位素的优先扩散损失，或者是由于SW/SEP通量比随时间的变化。此外，我们还证明了81氪浓度是流星体内部样品屏蔽深度的函数。吉林（H5）、丽水（L5）、随州（L6）和东台（LL6）的深度依赖曲线存在偏差。因此，确认了吉林的复杂暴露史，其他三个球粒陨石也有可能。宇宙射线暴露年龄是根据6种不同的核素——3 He， 21 Ne, 38 Ar, 83 Kr， 126 Xe和81 Kr-Kr来计算的。在大多数情况下，用不同的方法得出的年龄是一致的。对暴露年龄进行了质量分类，并讨论了年龄分布。在一些陨石中，我们观察到由次级宇宙射线产生的中子引起的效应。根据79 Br (n, γβ) 80 Kr和24 Mg (n, α) 21 Ne的反应，分别推导出超热中子通量J n （30-300 eV）和快中子通量J n (> 5 MeV)；并且估算了流星体的大气前质量。我们发现jn （30-300 eV）和jn （> - 5 MeV）的比值随大气前质量的增加而增加。我们提出了一个3 He暴露年龄/21 Ne暴露年龄vs. 4 He气体保留年龄/40 Ar气体保留年龄图，这是区分流星体不同热历史的有力工具。最后，在一些球粒陨石中，我们观察到了244pu裂变产生的Xe，并计算了这些球粒陨石中裂变-Xe保留的时间跨度与Angra dos Reis无球粒陨石的时间跨度。我们发现普通球粒陨石比Angra dos Reis早48±30 Ma开始保留裂变Xe；我们没有观察到H， L和LL或5型和6型球粒陨石在裂变Xe保留时间方面的系统差异。
We performed a comprehensive study of the noble gas isotopic abundances in thirty-six chondrites including twenty-seven chondrites recovered in China. The large data base allows us to recognize some new characteristics of the nuclear record in chondritic matter. The comparison of the trapped noble gas release pattern for ordinary and carbonaceous chondrites shows that the planetary trapped noble gases in ordinary chondrites are released mainly above 1200° C whereas≥ 85% of these gases in carbonaceous chondrites are degassed at≥ 200° C. There exists a clear correlation of the fraction of trapped Xe released at> 1200° C and petrologic type of chondrites. It thus appears that the carrier phases of the trapped noble gases in ordinary and in carbonaceous chondrites may not be the same. The Ngawi LL3 chondrite is solar gas rich. The solar gases in meteorites and lunar surface material are mixtures of solar wind (SW) and solar energetic particles (SEP). We show that the variations of the 3 He 4 He and 20 Ne 22 Ne ratios for solar gas-rich meteorites and lunar surface material could be either due to preferential diffusive losses of the lighter isotopes of He and Ne or due to a change of the SW/SEP flux ratio with time. Furthermore, we demonstrate that the 81 Kr concentration is a function of the shielding depth of a sample within the meteoroid. Deviations from this depth dependency curve are observed for Jilin (H5), Lishui (L5), Suizhou (L6), and Dongtai (LL6). A complex exposure history for Jilin is thus confirmed and is possible for the other three chondrites. Cosmic-ray exposure ages are calculated based on six different nuclides—3 He, 21 Ne, 38 Ar, 83 Kr, 126 Xe, and 81 Kr-Kr. In most cases good agreement is observed for the ages derived from the different methods. Quality classes are assigned to the exposure ages, and the age distributions are discussed. In some meteorites we observe effects induced by secondary cosmicray-produced neutrons. Epithermal neutron fluxes, J n (30–300 eV), and fast neutron fluxes, J n (> 5 MeV), are derived based on the reactions 79 Br (n, γβ) 80 Kr and 24 Mg (n, α) 21 Ne, respectively; and preatmospheric masses of the meteoroids are estimated. We show that the ratio J n (30–300 eV) J n (> 5 MeV) increases with increasing preatmospheric mass. We introduce a 3 He exposure age/21 Ne exposure age vs. 4 He gas retention age/40 Ar gas retention age diagram that is a powerful tool for distinguishing different thermal histories of meteoroids. Finally, in some chondrites we observe Xe produced by 244 Pu fission and calculate the time span between fission-Xe retention in these chondrites and that of the Angra dos Reis achondrite. We find that the ordinary chondrites started to retain fission Xe 48±30 Ma earlier than Angra dos Reis; we do not observe systematic differences between H, L, and LL or type 5 and 6 chondrites with respect to the time of fission Xe retention.
DOI：
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发表时间：
2007
期刊：
Lunar and Planetary Science Conference XXXVIII 38
影响因子：
--
作者：
原田 知明;保科 洋介;吉村 英恭;C.Okamoto
通讯作者：
C.Okamoto