Recent Fossil Track Studies Bearing on Extinct Pu²⁴⁴ in Meteorites

Abstract

Certain meteorites contain stored fission track densities that are in excess of those that can be attributed to the spontaneous fission of uranium. Previous work has shown that the most likely source of these tracks is the spontaneous fission of extinct Pu²⁴⁴. In this paper we present new results of two meteorites of particular interest. Preliminary measurements in Campo del Cielo (El Taco) and in Kodaikanal have been interpreted previously as giving evidence for a relatively high Pu/U ratio at the end of nucleosynthesis. The measurements reported here were made using improved techniques and are of much higher statistical weight. They do not confirm the earlier, preliminary work. The ratio of Pu to U fission tracks in Campo del Cielo (El Taco) is found to be 61 ± 14. This is consistent with eithere a sudden synthesis model or a continuous galactic synthesis model of heavy element production. The stored tracks in Kodaikanal appear to be due to heavy cosmic rays and are irrelevant to the Pu problem.