Lead and thallium isotopes in mare tranquillitatis surface material.
Lead from Apollo 11 fines is more radiogenic than any meteoritic lead reported and older than any terrestrial radiogenic lead: (201)Pb/(206)Pb/(207)Pb/(208)Pb = 1/99(.6)/69(.0)117(.1). Comparison with primordial lead from meteoritic troilite yields a 207Pb/ 206Pb age of 4.7 + 0.1 x 10(9) years. The (238)U/(204)Pb ratio is > 90 and the (232)Th/(238)U 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 (205)Pb.
Kohman
T P
TP
Black
L P
LP
Ihochi
H
H
Huey
J M
JM