太阳系^(53)Mn-^(53)Cr同位素体系

^(53)Mn-^(53)Cr Isotope Systematics in the Solar System

短周期放射性核素的初始丰度和分布情况,已成为陨石学和天体化学的重要研究领域之一。已有研究证实地外天体中53 Cr的放射性母体为53 Mn。53 Mn的半衰期为3.7±0.4Ma,可对太阳系形成之后的20Ma内发生的事件进行精确定年。本文系统总结了已报道的碳质球粒陨石、普通球粒陨石、顽辉石球粒陨石和分异陨石中的53 Mn-53 Cr同位素体系数据,依据55 Mn/52 Cr值和53 Cr异常探讨了太阳系形成时53 Mn和53 Cr的初始分布情况、太阳系初始的53 Mn/55 Mn值,讨论了陨石中普遍存在的54 Cr/52 Cr值异常和碳质球粒陨石全岩的54 Cr和53 Cr异常值之间的正相关关系对53 Mn-53 Cr体系定年影响。

High-precision measurements of chromium isotope compositions in meteorite samples revealed anomalies in the ^5aCr/^52Cr ratio,which are believed to arise from in situ decay of the extinct short-lived nuclide ^53Mn.The half life of ^53 Mn is 3.7 ± 0.4 Ma,the ^53 Mn-^53 Cr system,therefore,can potentially be a high-precision chronometer in constraining the formation time of the meteorite parent bodies in the early solar system if it was homogeneously distributed in the accretion disk.We summarized the latest studies of the Mn-Cr system of carbonaceous chondrites,ordinary chondrites,enstatite chondrites,differentiated meteorites and the acid leached fractions in the primitive carbonaceous chondrite in order to discuss the distribution of 5a Mn and 5a Cr in the early solar system and to estimate the initial ^53Mn/^55Mn ratio.Moreover,we discuss whether or not the spallation reactions produced by the cosmic ray and the co-variations in ε^54 Cr and ε^53 Cr for carbonaceous chondrites will affect the application of the Mn-Cr chronometry in meteorites.