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

• 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
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10640476/
• 关键词: lunar soil; aubrite; chondrite; cosmic-ray; neutron capture reaction; samarium; gadolinium; isotopic composition; 中性子捕獲; エネルギー共鳴; 隕石

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

测定了阿波罗12号和15号钻芯中7个月球样品中的Sm和Gd的同位素组成，讨论了月球表面附近中子俘获的影响。根据A- 12和A- 15样品的同位素位移计算的中子通量值分别为（1.77 ~ 2.17）× 10 γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ。变化的εィイD2SmィエD2 /εィイD2GdィエD2与深度解读为是由于中子能谱的变化。我们的数据表明，中子在低层比在上层更容易受热（Hidaka et al., in press）。这种方法被应用于陨石学。在5种辉长辉石无球粒陨石（长辉岩）中观测到中子俘获效应导致的巨大的γ γ γ γ γ - γ γ γ - γ γ - γ γ - γ γ - γ γ - γ - γ - γ - γ - γ。这些同位素的变化对应于（1.17-3.99）× 10 γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ。这些结果表明，权威岩可能在其母体表面附近存在了数百Ma。此外,中子能谱从Sm和Gd同位素分类学(εィイD2SmィエD2 /εィイD2GdィエD2)表明,在五aubrites热化中子的能量从200 ~ 400 K范围内,低于那些在a - 12和15月岩样本(Hidaka et al ., 1999)。8颗球粒陨石中Sm和Gd的同位素组成显示出中子捕获效应的证据，对应于热中子通量为（1.03 ~ 5.17）× 10 γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ。将8颗球粒陨石中4颗的Sm和Gd同位素结果与文献中Ne和Kr同位素数据计算的外热和快中子影响信息进行了比较。它们的热中子通量值与外热中子通量一致（Hidaka et al.，待提交）。少

项目成果

H.Hidaka: "Tc/Ru fractionation in the Oklo and Banombe natural fission reactors,Gabon"Chemistry Geology. 155. 323-333 (1999)

H.Hidaka：“加蓬 Oklo 和 Banombe 天然裂变反应堆中的 Tc/Ru 分馏”化学地质学。

H.Hidaka et al.: "High fluences of neutrons determined ftom Sm and Gd lstopic compositions in aubrites"Earth and Planetary Science Letters. 173. 41-51 (1999)

H.Hidaka 等人：“中子的高注量由金铜矿中的 Sm 和 Gd 同位素组成决定”，《地球与行星科学快报》。

H. HIDAKA: "Isotopic study of natural fission reactors at Oklo and Bangombe, Gaobn."J. Radioanal, Nucl. Chem., Article. 239. 53-58 (1999)

H. HIDAKA：“Oklo 和 Bangombe、Gaobn 天然裂变反应堆的同位素研究”。

H.Hidaka et al.: "Redistribution of fissiogenio and non-fissiogenic REE,Th and U in and around natural fission reactors at Oklo and Bangombe,Gabon"Geochimica et Cosmochimca Acta. (in press). (2000)

H.Hidaka 等人：“加蓬 Oklo 和 Bangombe 自然裂变反应堆内及周围裂变和非裂变 REE、Th 和 U 的重新分布”Geochimica et Cosmochimca Acta。

H. HIDAKA: "Isotopic analyses by using a Sensitive High Resolution Ion Micro-Probe (SHRIMP) for natural analogue study of Oklo and Bangombe, natural fission reactors."Radiochim. Acta.. 82. 327-330 (1998)

H. HIDAKA：“使用灵敏的高分辨率离子微探针 (SHRIMP) 进行同位素分析，对天然裂变反应堆 Oklo 和 Bangombe 进行天然模拟研究。”Radiochim。