Reports

Plutonium-244 Fission Tracks: Evidence in a Lunar Rock 3.95 Billion Years Old

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Science  26 May 1972:
Vol. 176, Issue 4037, pp. 909-911
DOI: 10.1126/science.176.4037.909

Abstract

Tracks attributed to the spontaneous fission of plutonium-244 and of uranium-238 were detected in a large whitlockite crystal in the lunar breccia 14321 from the Fra Mauro formation. For a track-retention age of 3.95 x 109 years the number of plutonium tracks relative to the number of uranium tracks is 0.51 ± 0.15, provided that the rock was not heavily neutron-irradiated 3.95 X 109 years ago.