An Impact Model of the Imbrium Basin for Distribution of Thorium on Lunar Surface

We consider the thorium distributions that are coincident with the distribution of ejecta after the Mare mbrium impact occurs on the lunar surface and derive a simple model on the spherical target to predict the thickness of Imbrium ejecta deposits as a function of distance from the centre of the Imbrium basin. Then we use the result of Lunar Prospector's gamma ray experiment to test the hypothesis that the distribution of thorium on the lunar surface has an origin from the Mare Imbrium.