SOLAR-FLARE-IMPLANTED HE-4 HE-3 AND SOLAR-PROTON-PRODUCED NE AND AR CONCENTRATION PROFILES PRESERVED IN LUNAR ROCK 61016

Documented near-surface samples from oriented lunar rock 61016 have yi elded the first measurements of depth profiles for Ne-21, Ne-22, and A r-38 isotopes produced in situ from nuclear interactions of energetic solar flare protons. Further, the cosmogenic Ne-21/Ne-22 ratios are di stinct for different proton energy ranges and increase systematically with increasing shielding. This variation in cosmogenic Ne-21/Ne-22 re presents a progression from a mixed component produced from solar flar e protons (SCR) and galactic cosmic rays (GCR) to a pure GCR component . Using the 2 m.y. exposure age for 61016, the calculated production r ates for SCR Ne-21 and Ar-38 from solar energetic protons in near-surf ace samples agree within 5% and 25%, respectively, with theoretical es timates. Calculated GCR production rates for Ne-21 and Ar-22 in the de epest (26 mm) samples agree within 25% and 10%, respectively, with the oretical estimates. Combined SCR and GCR concentration profiles for Ne -21/Ne-22, and Ar-38 match theoretical calculations based on an omnidi rectional flux above 10 MeV of 100 protons cm-2 s-1 with an exponentia l rigidity between 70 and 85 MV and a surface erosion rate of 1 mm m.y .-1. Selectively etched, near-surface samples suggest a long-term aver age He-4/He-3 ratio of approximately 770 for implanted solar flare nuc lei with E > approximately 4 MeV amu-1, and a He-4/He-3 ratio of appro ximately 3450 for solar flare nuclei with E > -1 McV amu-1. Averaged o ver long term, the solar flare He-4/He-3 ratio appears energy dependen t.