CONCENTRATIONS OF RADIOACTIVE ELEMENTS IN LUNAR MATERIALS

As an aid to interpreting data obtained remotely on the distribution o f radioactive elements on the lunar surface, average concentrations of K, U, and Th as well as Al, Fe, and Ti in different types of lunar ro cks and soils are tabulated. The U/Th ratio in representative samples of lunar rocks and regolith is constant at 0.27; K/Th ratios are more variable because K and Th are carried by different mineral phases. In nonmare regoliths at the Apollo sites, the main carriers of radioactiv e elements are mafic (i.e., 6-8% Fe) impact-melt breccias created at t he time of basin formation and products derived therefrom.