抄録
The problems in investigating the thermal history of the primordial solar nebula from the isotopic mass fractionation data are discussed based on the compiled data of primitive materials as well as on the results of reproducing experiments. The results of the experiments showed that isotopic mass fractionation is dominated by various conditions which may vary considerably in the nebula. The fractionation process is controlled for example by the state of the evaporation source, the rate of evaporation and the rate of source mixing as well as the molecular species of the gas phase. Hence at present, one cannot estimate the thermal origin of the large mass fractionation observed in the refractory inclusions of the primitive meteorites. In order to estimate the thermal history from the mass fractionation data, further experiments should be preformed to understand the kinetic behavior of molecules during the evaporation and condensation process in the nebula. At the same time, isotopic data should be accumulated over various mineral phases having different origins in the meteorite. The isotopic in-situ survey on sections of primitive material should be performed over a wide area with high spatial resolution for effective data accumulation.
