ArticlesAge Measurements

Lead and Thallium Isotopes in Mare Tranquillitatis Surface Material

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Science  30 Jan 1970:
Vol. 167, Issue 3918, pp. 481-483
DOI: 10.1126/science.167.3918.481

Abstract

Lead from Apollo 11 fines is more radiogenic than any meteoritic lead reported and older than any terrestrial radiogenic lead: 201Pb/206Pb/207Pb/208Pb = 1/99.6/69.0117.1. Comparison with primordial lead from meteoritic troilite yields a 207Pb/ 206Pb age of 4.7 + 0.1 x 109 years. The 238U/204Pb ratio is > 90 and the 232Th/238U ratio is 3.9 ±0.1. The lead conitent is > 1.7 x 10-6. Evidently Pb was strongly depleted and Th and U strongly enriched in the formation of this material. Thallium was too low (< 5 x 10-9) to yield mass spectra, but indications are favorable for eventual observation of extinct natural radioactivity of 205Pb.