THE FIRST LUNAR MAP OF THE AVERAGE SOIL ATOMIC MASS

Measurements of indexes of lunar surface composition were successfully made during Lunar Prospector (LP) mission, using the Neutron Spectrometers (NS) [1]. This capability is demonstrated for fast neutrons in Plates 1 of Maurice et al. [2] (similar to Figure 2 here). Inspection shows a clear distinction between mare basalt (bright) and highland terranes [2]. Fast neutron simulations demonstrate the sensitivity of the fast neutron leakage flux to the presence of iron and titanium in the soil [3]. The dependence of the flux to a third element (calcium or aluminum) was also suspected [4]. We expand our previous work in this study by estimating fast neutron leakage fluxes for a more comprehensive set of assumed lunar compositions. We find a strong relationship between the fast neutron fluxes and the average soil atomic mass: <A>. This relation can be inverted to provide a map of <A> from the measured map of fast neutrons from the Moon