Abstract We are continuing the development of a compact resonance ionization mass spectrometer for geochronology of planetary specimens, ultimately for in-situ use on the Moon or Mars. We previously demonstrated 87Rb–87Sr isochrons for the Martian meteorite Zagami and the Duluth Gabbro with a best precision for Zagami of 100 Myr, using 10-ns, 250-μJ laser ablation pulses of 213-nm radiation. In that work, we suggested that our precision had been limited by instabilities in the nanosecond ablation process, which strongly and variably fractionated Rb from Sr. To overcome this limitation, we have replaced the ablation laser with one generating 150-fs, 300-μJ pulses. Furthermore, by modifying the geometry of the sample to reduce plasma penetration into the mass spectrometer, we have improved our instrumental sensitivity, which in turn improves the dating precision we are able to achieve. Our age determination of 150 ​± ​20 ​Ma is 5 times more precise than our best previous reported age, and is no longer limited by the precision we can achieve on the Rb/Sr ratios of individual spots. Instead, we are now limited by the precision we can achieve in the 87Sr/86Sr ratios of the relatively few spots with the highest Rb/Sr ratios. We discuss prospects for even further improvements in the dating precision achievable with resonance ionization mass spectrometry.

中文翻译：

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使用原型原位测年仪以 20 Myr 的精度对火星陨石进行测年

摘要 我们正在继续开发用于行星标本地质年代学的紧凑型共振电离质谱仪，最终用于月球或火星的原位使用。我们之前使用 213 nm 辐射的 10 ns、250 μJ 激光烧蚀脉冲，展示了火星陨石 Zagami 和德卢斯辉长岩的 87Rb–87Sr 等时线，Zagami 的最佳精度为 100 Myr。在这项工作中，我们认为我们的精度受到纳秒烧蚀过程中的不稳定性的限制，该过程强烈且可变地将 Rb 从 Sr 中分离出来。为了克服这一限制，我们用一个产生 150-fs、300-μJ 的烧蚀激光器代替了烧蚀激光器脉冲。此外，通过修改样品的几何形状以减少等离子体对质谱仪的渗透，我们提高了仪器灵敏度，这反过来又提高了我们能够实现的测年精度。我们对 150 ± 20 Ma 的年龄测定比我们之前报道的最佳年龄精确 5 倍，并且不再受我们在单个点的 Rb/Sr 比率上所能达到的精确度的限制。相反，我们现在受限于我们在 87Sr/86Sr 比率中可以达到的精度的限制，这些点的 Rb/Sr 比率相对较少。我们讨论了进一步提高共振电离质谱法可实现的测年精度的前景。我们现在受限于我们在 87Sr/86Sr 比率中可以达到的精度的限制，这些点具有最高的 Rb/Sr 比率。我们讨论了进一步提高共振电离质谱法可实现的测年精度的前景。我们现在受限于我们在 87Sr/86Sr 比率中可以达到的精度的限制，这些点具有最高的 Rb/Sr 比率。我们讨论了进一步提高共振电离质谱法可实现的测年精度的前景。