Nitrogen isotope systematics of two Apollo 12 soils

Soils 12023 and 12037 were analyzed for nitrogen by step-wise heating. Helium contents, Ar-40/Ar-36 ratios and spallation N-15 ages were determined in addition to nitrogen contents and isotopic compositions. The results for 12023 show it to be a typical lunar soil similar to many Apollo 16 and 17 soils in its nitrogen content and delta N-15 value, with a complex history. Soil 12037 appears to have had a simple, two-stage surface exposure history; one exposure occurring recently for about 10-20 m.y. and the other between about 3 to 4 b.y. ago. The delta N-15 value of nitrogen implanted in the earlier exposure was -125%. This nitrogen may reside in the minor components of 12037 such as the KREEP. If it should reside in the basaltic component of 12037, however, then the variation in the delta N-15 of implanted nitrogen with time probably has been more complex than previously considered.