Actinide Chemistry of Allende Components

U and Th in inclusions. Previous reports of high Th/U in Allende Ca,Al-rich inclusions (Boynton, 1978; Chen and Wasserburg, 1981; Stapanian, 1981) may indicate that U was not acting as a refractory element. The apparent ease of Th/U fractionation in the earliest material makes the ubiquity of Th/U = 3.8 in the solar system hard to understand. U-Th fission track radiography offers the possibility of a better understanding of actinide chemistry in Allende Ca,Al-rich inclusions. Volatility and valence differences between Th and U make these elements potentially useful in distinguishing between primary (condensation?) characteristics and those produced later by alteration. A preliminary examination of TS-23 (a type B inclusion provided by L. Grossman, 1975) shows U to be highly enriched in the inclusion rim. This result is qualitatively similar to that found for U and Th in type A inclusions by Stapanian (1981).