Abstract
THE concentration of polonium-210 has been measured in the Solar Wind Composition (SWC) experiment foils which were exposed on the surface of the Moon by the Apollo 11 and Apollo 12 astronauts. These data permit a direct calculation of the equilibrium lunar atmospheric content of radon-222 which Kraner et al.1 had estimated to be 4 disintegrations cm−2 s−1 using terrestrial values of the radon diffusion coefficient and uranium concentration and assuming a lunar surface porosity of 0.25. In 1969 Yeh and Van Allen2 set upper limits for the alpha-particle emissivity of the Moon which indicated the radon-222 concentration was at least an order of magnitude lower than the provisional estimates of Kraner. Their calculations were based on alpha flux measurements made by a totally depleted gold–silicon surface barrier detector on the Moon-orbiting spacecraft, Explorer 35.
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