An extrapolation method for the determination of Cliff‐Lorimer k_AB factors at zero foil thickness

An extrapolation method is proposed to be useful for the determination of the Cliff‐Lorimer k_AB factor at zero foil thickness. The method consists of measuring k_AB factors as a function of the measured foil thickness, t_M, and extrapolating the relationship toward t_M=0. The intersection between the extrapolated line and the ordinate of t_M=0 gives (k_AB)₀ which is free from the effect of absorption. The straight line extrapolation that can be achieved by a linear‐least squares method is particularly developed to eliminate arbitrariness introduced in the extrapolation process. The extrapolation method is applied to data available in the literature. It is shown that the method yields the (k_AB)₀ factors compatible with those predicted from the theoretical calculation. It is also shown that this method can circumvent several problems which make it complex and difficult to determine accurate values of the absorption‐free k_AB factors. Using the straight line extrapolatioin, it is possible to estimate the degree of the thickness overestimation which arises when the foil thickness is measured by the contamination spot separation (CSS) method. Validity of the straight line extrapolation is further discussed. 1986 Blackwell Science Ltd