Spectral Reflectance of Solids for Aluminum K Radiation*

Abstract

The fraction of aluminum K radiation reflected from flat glass, magnesium, aluminum, copper, silver, and gold surfaces was measured as a function of the angle of grazing incidence. A single vacuum chamber enclosed the 0.01 in. diameter, aluminum wire anode x-ray tube, 15-μ thick absorption filter, CeBr(Tl) scintillator, refrigerated 6199 photomultiplier, reflecting surface, and metal evaporation source. The metallic surfaces were films deposited on glass flats already placed in position for immediate reflectance measurements. A linkage caused the x-ray beam to impinge on a fixed portion of the scintillator to avoid detector nonuniformities, and the photomultiplier-detector was cooled with ice water to reduce thermal noise.Excluding two anomalous cases, the critical angles average 9.3% below theoretical calculated values, and absorption ratios 28.2% above. A reduced material density could account for the low critical angle, but no simple explanation was conceived to account for the absorption discrepancy. Interference extremes produced by reflection from the aluminum film were in agreement with predictions of a revised interference theory.