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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >High fluences of neutrons determined from Sm and Gd isotopic compositions in aubrites
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High fluences of neutrons determined from Sm and Gd isotopic compositions in aubrites

机译：由铝土矿中Sm和Gd同位素组成确定的中子高通量

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摘要

Large isotopic deviations of ~(149)Sm-~(150)Sm and ~(157)Gd-~(158)Gd derived from neutron capture effects were observed in five enstatite achondrites (aubrites); Norton County, ALH78113, Cumberland Falls, Bishopville and Mayo Belwa. The isotopic variations of these aubrites (#epsilon#~(149)Sm = -32 to -7, #epsilon#~(150)Sm = +11 to +57, #epsilon#~(157)Gd = -42 to -14 and #epsilon#~(158)Gd = +9 to +26) correspond to irradiation with neutron fluence of (1.17 - 3.99) * 10~(16) n cm~(-2), which is within the range of estimated neutron fluence values of some lunar samples. These results indicate that aubrites may have been located near the surface of their parent body for several hundreds of Ma. Furthermore, the neutron energy spectrum obtained from the combination of Sm and Gd isotope systematics (#epsilon#_(Sm)/#epsilon#_(Gd)) suggests that the energy of thermalized neutrons in five aubrites was in the range of 200-400 K, and was lower than those in lunar samples A-12 and A-15. In addition, we analyzed one anomalous aubrite (Mt. Egerton), and two enstatite chondrites (Happy Canyon and Abee) to investigate the relationship of their origin with aubrites. However, these three meteorites showed no evidence for intensive neutron irradiation observed in the aubrites.
机译：在5个顽辉长晶陨石（球铁矿）中观察到中子俘获效应引起的〜（149）Sm-〜（150）Sm和〜（157）Gd-〜（158）Gd的大同位素偏差;诺顿县，ALH78113，坎伯兰瀑布，毕晓普维尔和梅奥·贝尔瓦。这些土质的同位素变化（＃epsilon＃〜（149）Sm = -32至-7，＃epsilon＃〜（150）Sm = +11至+57，＃epsilon＃〜（157）Gd = -42至- 14和＃epsilon＃〜（158）Gd = +9至+26）对应于中子注量为（1.17-3.99）* 10〜（16）n cm〜（-2）的辐射，这在估计范围内一些月球样品的中子注量值。这些结果表明，成矿剂可能位于其母体表面附近数百Ma。此外，从Sm和Gd同位素系统学组合获得的中子能谱（#epsilon #_（Sm）/＃epsilon #_（Gd））表明，五个奥氏体中热化中子的能量在200- 400 K，低于月球样品A-12和A-15中的样品。此外，我们分析了一种异常的钠长石（埃格顿山）和两种顽辉的球粒陨石（欢乐峡谷和阿比），以研究其起源与钠长石的关系。但是，这三个陨石没有显示出在铁素体中观察到强中子辐照的证据。

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