Fossil Particle Tracks and Uranium Distributions in Minerals of the Vaca Muerta Meteorite.

Fossil tracks of charged particles have been observed in minerals separated from the Vaca Muerta mesosiderite. Irradiation of samples of the meteorite with thermal neutrons in a nuclear reactor, together with measurements of track-length distribution, indicate that some of the tracks result from the spontaneous fission of uranium impurities; others, however, are of different origin. Uranium concentrations, which ranged from about 4000 parts per million in a zircon grain to less than 10(-3) parts per million in hypersthene and anorthite, were also measured by irradiating samples with thermal neutrons.