Investigation of the Rayleigh Critical Angle Phenomenon for the Characterization of Surface Properties.

An automated, computer controlled goniometer was constructed and perfected. Controlled measurements on a variety of materials, including materials of interest to the NDT community, were carried out and compared with theoretical predictions made by a number of authors. Experimental results indicate that these theories may be only first approximations to reality. A number of significant experimental anomalies, such as the appearance of more than one amplitude dip were found. Certain theoretical questions were raised regarding these theories including the question of momentum conservation at the interface. Both the experimental and theoretical observations suggest that modifications to existing theory may be necessary. Author