Geochemical Study on the Oldest Halite Fossil in the Solar System

卤素和它们的晶体（卤化物）已经在Zag和其他含卤素的陨石中进行了研究，通过检测来自灭绝核素的卤素衍生的惰性气体同位素^<80>Kr，^<82>Kr和^<128>Kr，<129>以及^ I<129>也在这些陨石中测量到。卤化物晶体是Zag陨石的暗相部分。大多数晶体的尺寸估计小于0.1 mm，这将被不溶于水的硅酸盐包围。在Yamato-74191（L3.6）陨石中，卤素也集中在小的物质中。这些陨石中的卤素富集可能是由于其母星子上存在高浓度卤素的液态水。虽然这些沃茨的来源尚不清楚，但它们可能是由含水的物体（如碳质陨石或彗星）轰击而带来的。为了研究与卤素富集有关的事件，我们建造了惰性气体提取和纯化线，用于中子辐照陨石的惰性气体分析。对<40><39>东京大学放射性同位素中心的VG 3600惰性气体质谱计进行了改进，以提高其灵敏度和稳定性。结合惰性气体线和质谱仪，在日本首次可以测量陨石的I-同位素年龄。这一方法开始阐明陨石中卤素富集过程的时间。

Halogens and their crystals (halide) have been investigated in Zag and other halogen containing meteorites by detecting halogen-derived noble gas isotopes ^<80>Kr, ^<82>Kr and ^<128>Xe^<129>Xe from extinct nuclide was ^<129>I also measured in these meteorites. Halide crystals are dark phase portion of the Zag meteorite. Size of most crystals are estimated to be smaller than 0.1 mm, which would be surrounded by silicates insoluble in water. Halogens are also concentrated in small materials in Yamato-74191 (L3.6) meteorite. The halogen enrichments in these meteorite are likely resulted by liquid water with high concentrations of halogens presented on their parent planetesimals. Though origin of the waters is not clear, they might have been brought through bombardment by water containing objects such as carbonaceous chondrites or comets.To study the event concerning the halogen enrichments, we constructed noble gas extraction and purification line for noble gas analysis of neutron irradiated meteorites. Modification of VG3600 noble gas mass spectrometer used for ^<40>Ar-^<39>Ar dating was carried out to improve sensitivity and stability of the mass spectrometer in the Radioisotope Center, University of Tokyo. Combining the noble gas line and the mss spectrometer, I-Xe dating of meteorites can be measurable for the first time in Japan. This method began to clarify the timing of halogen enrichment process in meteorites.