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A new astronomy with radioactivity: Radiogenic carbon chemistry

机译：放射性的新天文学：放射性碳化学

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Historically it has been assumed that the necessary condition for carbon solids to grow in a cooling gas is higher bulk C abundance than 0 abundance. That condition is observed to be necessary and valid in AGB red-giant stars, inducing more general acceptance of that requirement. But for hydrogen-free supernova interiors that bulk-abundance condition is too restrictive. Within their expanding and cooling interiors, radioactivity maintains a prolific source for new free C. Very abundant CO molecules cannot retain oxidized carbon owing to their dissociation by energetic free electrons, which are created continuously by Compton scattering of gamma rays from newly created radioactive ~(56)Co nuclei. As the local gas temperature cools below 2000 K the free C atoms condense as carbonaceous grains, even in the presence of more abundant 0 atoms. The necessary conditions within supernovae must instead be expressed by three new rules: 1. Free C atoms must exist abundantly. An abundance ratio C/O > 1 would indeed suffice for that end, but it is not necessary. Maintenance of abundant free C atoms occurs by radioactivity dissociating abundant CO molecules and also by lack of sufficient expansion time for complete oxidation of free C. 2. Chemical reaction networks associating C atoms into C solids must be kinetically faster than their oxidation. That is, free C must be able to grow C solids faster than those solids can be oxidized. 3. Insufficient time for oxidation of the new carbon solids must exist after the eventual depletion of free carbon prior to ejection into the interstellar medium. Those C solids could be termed metastable because they would be absent but for the chemical consequences of the radioactivity. 1 present some calculations for these expectations elaborating on figures from published works. The chemical dynamics provide a new discipline of astronomy with radioactivity in young supernova remnants. Carbonaceous supernova condensates (graphite and silicon carbide) extracted from meteorites provide abundant isotopic evidence of dynamic details of young supernova remnants. But expertise from molecular and chemical dynamics is needed to bring the theory to fruition.
机译：历史上已经假设，碳固体在冷却气体中生长的必要条件是体积C丰度高于0丰度。该条件在AGB红巨星中被认为是必要且有效的，从而引发了对该要求的更普遍的接受。但是对于无氢超新星内部来说，其丰度条件太过严格。在其不断膨胀和冷却的内部空间中，放射性维持着大量新自由C的来源。非常丰富的CO分子由于被高能自由电子解离而无法保留氧化碳，高能自由电子是由新产生的放射性〜的伽马射线的康普顿散射连续产生的。 56）核当局部气体温度降到2000 K以下时，即使存在大量0原子，游离的C原子也会凝结为碳质颗粒。相反，超新星内部的必要条件必须由三个新规则表示：1.自由C原子必须大量存在。为此，丰度比C / O> 1确实足够，但这不是必需的。大量游离C原子的维持是通过放射性使大量CO分子解离，也由于缺乏足够的膨胀时间而无法完全氧化游离C来实现的。2.将C原子缔合为C固体的化学反应网络在动力学上必须比其氧化快。也就是说，游离的C必须比那些被氧化的固体更快地生长C的固体。 3.在最终的自由碳耗尽之后，在喷射到星际介质中之前，必须存在足够的时间来氧化新的碳固体。那些C固体可以被称为亚稳态，因为除了放射性的化学后果外，它们将不存在。 1给出了对这些期望的一些计算，这些期望是根据已发表作品中的数字进行阐述的。化学动力学为天文学的新学科提供了新的超新星遗迹的放射性。从陨石中提取的碳质超新星冷凝物（石墨和碳化硅）为年轻超新星残余物的动态细节提供了丰富的同位素证据。但是需要分子和化学动力学方面的专业知识才能使理论付诸实践。

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    《New astronomy reviews》 |2011年第6期|p.155-165|共11页
  • 作者

    Donald D. Clayton;

  • 作者单位

    Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634, USA;

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