The influence of cosmic-ray production on extinct nuclide systems
The influence of cosmic-ray production on extinct nuclide systems
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DOI：
10.1016/s0016-7037(02)01091-8
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发表时间：
2003-02-01
影响因子：
5
通讯作者：
Halliday, AN
中科院分区：
文献类型：
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作者：
Leya, I;Wieler, R;Halliday, AN
陨石和月球样本中 Cr-53、Zr-92、Ru-98、Ru-99 和 W-182 原子丰度相对于地面值的变化可能分别意味着放射性 Mn-53、Nb-92、Tc-98、Tc-99 和 Hf-182 的早期衰变。由此可以推断出核合成地点和早期太阳系的时间尺度。由于这些影响非常小，因此宇宙射线相互作用产生和消耗相应同位素是一个令人担忧的问题。最近已经证明，Ta-181 上的中子俘获反应产生的 W-182 对于大多数月球样品至关重要（Leya 等人，2000a）。在这项研究中，每个样品的中子注量是根据其标称宇宙射线暴露年龄（从惰性气体数据推导出来的）来估计的。这种方法高估了可能在非常接近风化层表面受到辐射的样本的真实宇宙成因同位素变化。因此，在这里我们将模型计算与中子剂量代理 Gd-157/Gd-158 和 Sm-149/Sm-150 结合起来。这使我们能够通过测量等分试样中的 Gd-157/Gd-158 和/或 Sm-149/Sm-150 来准确校正测量的 W 同位素数据，以了解宇宙射线引起的位移，而无需明确了解样品的暴露年龄或屏蔽深度。此外，我们还提出了 GCR 对 Mn-53-Cr-53、Nb-92-Zr-92 和 Tc-98-Tc-99-Ru-98-Ru-99 诱导效应的新模型结果。对于这些系统中的每一个，除了 Tc-Ru 之外，都给出了适当的宇宙射线剂量代理，从而可以准确校正测量的宇宙成因贡献的同位素比率。版权所有 (C) 2003 爱思唯尔科学有限公司
Variations in the atomic abundances of Cr-53, Zr-92, Ru-98, Ru-99, and W-182 in meteorites and lunar samples relative to terrestrial values may imply the early decay of radioactive Mn-53, Nb-92, Tc-98, Tc-99 and Hf-182, respectively. From this one can deduce nucleosynthetic sites and early solar system timescales. Because these effects are very small, production and consumption of the respective isotopes by cosmic-ray interactions is a concern. It has recently been demonstrated that W-182 production by neutron capture reactions on Ta-181 is crucial for most lunar samples (Leya et al., 2000a). In this study the neutron fluence of each sample was estimated from its nominal cosmic-ray exposure age as deduced from noble gas data. This approach overestimates the true cosmogenic isotopic shift for samples that might have been irradiated very close to the regolith surface. Here we therefore combine our model calculations with the neutron dose proxies Gd-157/Gd-158 and Sm-149/Sm-150. This allows us to accurately correct the measured W isotopic data for cosmic-ray induced shifts without the explicit knowledge of the exposure age or the shielding depth of the sample simply by measuring Gd-157/Gd-158 and/or Sm-149/Sm-150 in an aliquot. In addition we present new model results for the GCR-induced effects on Mn-53-Cr-53, Nb-92-Zr-92 and Tc-98-Tc-99-Ru-98-Ru-99. For each of these systems, except Tc-Ru, a proper cosmic-ray dose proxy is given, permitting the accurate correction of measured isotopic ratios for cosmogenic contributions. Copyright (C) 2003 Elsevier Science Ltd.