The α‐scattering technique of chemical analysis as used on the Surveyor lunar missions is described. Improved α sources and methods of data analyses lead to appreciably better results than those achieved previously by this technique. The accuracy of the α‐scattering method has been tested through the analysis of eleven rocks of known composition using a space Surveyor instrument. These results have provided the basis for estimation of the errors of the lunar surface analyses on Surveyors 5, 6, and 7. Some nonstandard geometrical relationships of sample to instrument, such as were encountered on the Surveyor missions, have been studied and their effects estimated. As a by‐product of this work, chemical analyses of five rocks of unknown composition were obtained.
The last three Surveyor missions (5, 6, and 7) included an α‐scattering experiment that obtained elemental analyses of surface material at three widely separated locations on the moon. On Surveyor 7, three different samples were analyzed at a terra site near the crater Tycho. These samples are much alike in composition but differ from the mare samples of Surveyors 5 and 6 in their lower content of ‘iron’ (elements approximately of mass 56). The analyses at all three sites are similar to the compositions of some of the most common rocks found on the earth's surface, such as basalts, but are quite different from the compositions of ultrabasic rocks and chondritic meteorites. The analyses at the three sites make possible the prediction of the chemical and physical properties of lunar surface material. The difference between the analyses of the mare and terra samples may contribute to the difference in albedo of these two types of material and may also indicate geological separation of lunar materials of varying density, as has happened on earth.
Evidence has been obtained for a radioactive deposit on the lunar surface at Mare Tranquillitatis with a total intensity of 0.09 +/- 0.03 alpha disintegration per second per square centimeter. The presence of polonium-210 in amounts that are close to equilibrium indicates a continuous turnover rate of lunar material at this site of less than 0.1 micrometer per year. The lack of such a deposit at two other lunar sites suggests lower local concentrations of uranium there.
More precise and comprehensive analytical results for lunar material in Sinus Medii have been derived from the alpha-scattering experiment on Surveyor VI. The amounts of the principal constituents at this mare are approximately the same as those of constituents at Mare Tranquillitatis. The sodium contents of both maria are lower than those of terrestrial basalts. The titanium content at Sinus Medii is lower than that at Mare Tranquillitatis; this suggests important differences in detailed chemical composition at different mare areas on the moon.
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