The chemical a n a l y s i s of s u r f a c e s u s i n g a l p h a p a r t i c l e i n t e r a c t i o n s h a s been i n v e s t i g a t e d . Simple i n s t r u m e n t s i n c o r p o r a t i n g Cm 242 a l p h a sources and semiconductor s i l i c o n d e t e c t o r s a r e d e s c r i b e d . The c h a r a c t e r i s t i c energy s p e c t r a of a l p h a p a r t i c l e s s c a t t e r e d a t l a r g e a n g l e s from t h i c k t a r g e t s of d i f f e r e n t elements have been d e t e r m i n e d . The r e l a t i v e i n t e n s i t i e s of s c a t t e r i n g by d i f f e r e n t elements have been e s t a b l i s h e d . They show l a r g e enhancement over Rutherford s c a t t e r i n g f o r elements l i g h t e r t h a n sodium due t o n u c l e a r e f f e c t s . The production o f p r o t o n s from ( a , p ) r e a c t i o n s i n c e r t a i n elements i n c r e a s e s t h e s e n s i t i v i t y of t h e method f o r t h e s e elements. The t h e o r e t i c a l basis f o r t h e q u a n t i t a t i v e i n t e r p r e t a t i o n of s c a t t e r i n g s p e c t r a from complex materials i s developed. The technique appears to be s u i t a b l e f o r instrumented space missions.

The chemical composition of the lunar surface material at a maria landing site has been determined by the alpha-scattering technique. Oxygen, silicon, and aluminum have been identified in the preliminary evaluation of the data. The general chemical composition is similar to that of a silicate of a basaltic type.

More precise and comprehensive analytical results have been derived for lunar material at the Surveyor V landing site from alpha-scattering data. The composition is, in general, basaltic; the low sodium and high titanium contents, however, are distinctly different from the abundances in meteorites or common terrestrial rocks.

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.