Exposure histories of the lunar meteorites - MAC88104, MAC88105, Y791197, and Y86032

Four lunar meteorites were analyzed for the cosmogenic radionuclides Be-10, Al-26, Cl-36, and Ca-41. Histories of exposure to cosmic rays were modelled in terms of two-stage irradiations, each with a long first stage on the moon, lasting a time T sub 2pi greater than 5 Ma at a burial depth d sub 2pi(g/sq cm), followed by a second stage in space, i.e., the transit time between the moon and the earth, lasting a time T sub 4pi (Ma) in a body of typical metereological size. It is inferred that the production rate is of the order of 5/Ma and the arrival rate worldwide is about 3,000,000 meteorites/Ma. It is concluded that each impact event large enough to produce lunar meteorites sends a large number of them to the earth.