Microanalysis of Materials by Backscattering Spectrometry

Abstract

After its successful soft landing on the moon on 9 September 1967, Surveyor 5 transmitted back to earth signals which contained the first factual information on the chemical composition of the lunar soil. The data were obtained from the "alpha-scattering experiment" performed by a relatively simple instrument placed on the lunar soil. A radioactive source emitted alpha particles which were directed at the lunar surface. The particles were then scattered back by collisions with the constituent atoms of the lunar material and counted by suitably positioned, energy-sensitive detectors. From such measurements one can determine the mass of the collision partner and therefore identify the elements present in the soil (1, 2). These backscattering analyses agree remarkably well with the chemical analyses later made on samples of moon rocks returned to earth by the Apollo 11 and Apollo 12 missions (3).