title: Trace elements and radioactivity in lunar rocks: implications for meteorite infall, solar-wind flux, and formation conditions of moon.
abstract: Lunar soil and type C breccias are enriched 3-to 100-fold in Ir, Au, Zn, Cd, Ag, Br, Bi, and Tl, relative to type A, B rocks. Smaller enrichments were found for Co, Cu, Ga, Pd, Rb, and Cs. The solar wind at present intensity can account for only 3 percent of this enrichment; an upper limit to the average proton flux during the last 4.5 x 109 years thus is 8 x 10(9) cm(-2) yr(-1). The remaining enrichment seems to be due to a 1.5 to 2 percent admixture of carbonaceous-chondritelike material, corresponding to an average influx rate of meteoritic and cometary matter of 2.9 x 10(-9) g cm(-2) yr(-1) at Tranquility Base. This is about one-quarter the terrestrial rate. Type A, B rocks are depleted 10-to 100-fold in Ag, Au, Zn, Cd, In, Tl, and Bi, relative to terrestrial basalts. This suggests loss by high-temperature volatilization, before or after accretion of the moon. Positron activities due mainly to (22)Na and (26)Al range from 90 to 220 beta(+) min(-1) kg(-1) in five small rocks or fragments (9 to 29 g). The higher activities presumably indicate surface locations. Th and U contents generally agree with those found by the preliminary examination team.
authors.forename: R R
authors.initials: RR
authors.lastname: Keays
authors.forename: R
authors.initials: R
authors.lastname: Ganapathy
authors.forename: J C
authors.initials: JC
authors.lastname: Laul
authors.forename: E
authors.initials: E
authors.lastname: Anders
authors.forename: G F
authors.initials: GF
authors.lastname: Herzog
authors.forename: P M
authors.initials: PM
authors.lastname: Jeffery