Estimation of Absolute Number Densities from Shapes of Atomic Fluorescence Curves of Growth

Abstract

A general-purpose computer program has been developed to calculate atomic fluorescence curves of growth (COG) for a wide variety of cases and particularly for the experimentally interesting cases where the excitation source spectral bandwidth is not much different from the absorption linewidth in typical flames and plasmas. Calculations over a wide range of the variables which affect the shape of the COG in the high-number-density region show that the point of departure from linearity can be used to predict the absolute number density in the atomizer cell. For resonance atomic fluorescence, the point at which the experimental curve of growth is twofold below the low-density linear asymptote invariably occurs at a k0 L (peak absorption coefficient × absorption pathlength) product of 2 ± 1. Number densities can easily be determined to within an order of magnitude accuracy, even when such variables as source spectral width, collection geometry, and damping parameter are totally unknown. In favorable circumstances, where such variables are well known, accuracies of ±10% may be obtained. The calculated curves of growth are in excellent agreement with several COGs which have been experimentally obtained.