Determination of the energy spectrum of secondary neutron flux for lunar samples and its application for meteoritics

月球样品二次中子通量能谱测定及其在陨石学中的应用

基本信息

批准号：
10640476
负责人：
HIDAKA Hiroshi
金额：
$ 2.5万
依托单位：
Hiroshima University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

The isotopic compositions of Sm and Gd in seven lunar samples from the Apollo 12 and 15 drill cores were determined to discuss the effects of neutron capture near the lunar surface. Neutron fluence values calculated from the isotopic shifts of A- 12 and A- 15 samples were (1.77 - 2.17) x10ィイD116ィエD1ncmィイD1-2ィエD1 and (3.02 - 4.68)x10ィイD116ィエD1 n cmィイD1-2ィエD1, respectively. Variations of εィイD2SmィエD2/εィイD2GdィエD2 with depth are interpreted as due to variations in the neutron energy spectrum. Our data suggest that the neutron is more thermalized at the lower layers than it is at the upper layers (Hidaka et al., in press).This approach was applied for meteoritics. Large isotopic deviations of ィイD1149ィエD1Sm-ィイD1150ィエD1Sm and ィイD1157ィエD1Gd-ィイD1158ィエD1Gd derived from neutron capture effects were observed in five enstatite achondrites (aubrites). The isotopic variations of these aubrites correspond to irradiation with neutron fluence of (1.17-3.99)x10ィイD116ィエD1 n cmィイD1-2ィエD1 which is within the … More 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 (εィイD2SmィエD2/εィイD2GdィエD2) suggests that the energy of thermalized neutrons in five aubrites was in the range from 200 〜 400 K, and was lower than those in A-12 and A-15 lunar samples (Hidaka et al., 1999). Isotopic compositions of Sm and Gd in eight chondrites show an evidence of neutron capture effects in the chondrites, correspond to thermal neutron fluences of (1.03 〜 5.17)x10ィイD115ィエD1 n cmィイD1-2ィエD1. The Sm and Gd isotopic results of four of eight chondrites were compared with information on epi-thermal and fast neutron fluences calculated from literature Ne and Kr isotopic data. Thermal neutron fluence values of them are in agreement with epi-thermal neutron fluences (Hidaka et al., to be submitted). Less

测定了来自阿波罗 12 号和 15 号钻芯的 7 个月球样品中的 Sm 和 Gd 同位素组成，以讨论根据 A-12 和 A- 的同位素位移计算出的中子注量值对月球表面附近的捕获的影响。 15 个样品为 (1.77 - 2.17) x10D116D1NCMD1-2D1 和(3.02 - 4.68)x10D116D1 n cmD1-2D1 εD2SmD2/εD2Gd2 随深度的变化被解释为由于中子能谱的变化，我们的数据表明中子在较低层比在较高层热化程度更高。上层（Hidaka 等人，该方法应用于陨石学。在五种顽辉石无球粒陨石（赤辉石）中观察到源自中子俘获效应的 D1149D1Sm-D1150D1Sm 和 D1157D1Gd-D1158D1Gd 的大同位素偏差。中子注量为 (1.17-3.99)x10D116D1 n cmD1-2D1 的辐照，在一些月球样本的估计中子注量值范围内。这些结果表明赤赤核星体可能位于其母体表面附近。此外，结合 Sm 和 Gd 同位素系统学获得的中子能谱。 (ε-D2Sm-D2/ε-D2Gd-D2)表明，五个赤铜体中的热化中子能量在200至400 K范围内，并且低于A-12和A-15月球样本中的热化中子能量(Hidaka)等人，1999）八颗球粒陨石中 Sm 和 Gd 的同位素组成表明球粒陨石中的中子俘获效应，对应于 (1.03 至 5.17)x10cmD1-2D1 的热中子注量。将八个球粒陨石中的四个的 Sm 和 Gd 同位素结果与根据文献 Ne 和计算的超热中子注量信息进行了比较。氪同位素数据。它们的注量值与超热中子注量一致（Hidaka等人，待提交）。