We determined interstellar cosmic ray exposure ages of 40 large presolar silicon carbide grains extracted from the Murchison CM2 meteorite. Our ages, based on cosmogenic Ne-21, range from 3.9 ± 1.6 Ma to ∼3 ± 2 Ga before the start of the Solar System ∼4.6 Ga ago. A majority of the grains have interstellar lifetimes of <300 Ma, which is shorter than theoretical estimates for large grains. These grains condensed in outflows of asymptotic giant branch stars <4.9 Ga ago that possibly formed during an episode of enhanced star formation ∼7 Ga ago. A minority of the grains have ages >1 Ga. Longer lifetimes are expected for large grains. We determined that at least 12 of the analyzed grains were parts of aggregates in the interstellar medium: The large difference in nuclear recoil loss of cosmic ray spallation products 3He and 21Ne enabled us to estimate that the irradiated objects in the interstellar medium were up to 30 times larger than the analyzed grains. Furthermore, we estimate that the majority of the grains acquired the bulk of their cosmogenic nuclides in the interstellar medium and not by exposure to an enhanced particle flux of the early active sun.

中文翻译：

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太阳系前碳化硅的宇宙射线暴露年龄产生的星际尘埃的寿命。

我们确定了从Murchison CM2陨石中提取的40个大型太阳前大碳化硅晶粒的星际宇宙射线暴露年龄。在宇宙系Ne-21的基础上，我们的年龄在太阳系开始4.6 Ga之前的3.9±1.6 Ma到〜3±2 Ga。大多数谷物的星际寿命小于300 Ma，这比大谷物的理论估计值要短。这些晶粒凝结在<4.9 Ga的渐近巨型分支恒星流出中，这可能是在增强的恒星形成〜7 Ga之前发生的。少数谷物的年龄> 1 Ga。大谷物的使用寿命更长。我们确定至少12个被分析的谷物是星际介质中聚集体的一部分：宇宙射线散裂产物3He和21Ne的核后坐力损失相差很大，使我们能够估计星际介质中被辐照的物体最多是所分析谷物的30倍。此外，我们估计大多数谷物是在星际介质中获得了大部分的宇宙核素，而不是通过暴露于早期活跃太阳的增强粒子通量获得的。