Plutonium-244 dating VI. Initial ratios of plutonium to uranium in achondrites

Re-examination of all known xenon isotopic data for achondrites reveals that244Pu fission xenon can be resolved in about three-fourths of the meteorites of this class. The amounts of244Pu fission xenon found in these meteorites range from ca. 1–2 up to 20–40·10−12 ccSTP/g. These meteorites started to retain their xenon some 200–500 million years later than did the carbonaceous chondrites Allende, Groznaya, Mokoia, Murchison, Murray, and Renazzo, which began to retain their xenon over 4800 million years ago.