PU-244 IN THE EARLY SOLAR-SYSTEM

An attempt has been made to calculate the ages of lunar fines and carb onaceous chondrites from the contents of Pu-244 fission xenon and uran ium. The carbonaceous chondrites such as Renazzo and Allende appear to be the oldest objects in the solar system and they began to retain th eir xenon about 4,900 million years ago when the ratio of Pu-244 to U- 238 in the solar system was about 0.123 (atom/atom). Lunar fines, whic h appear to be the second oldest objects in the solar system, began to retain their xenon 4,568 to 4,857 million years ago, when the ratio o f Pu-244 to U-238 was 0.0078 to 0.0855 (atom/atom).