Rutherford backscattering (RBS) of helium ions seems to be a feasible method for the depth analysis of fluorine. Targets of thickness between 30 and 3B24/250of calcium fluoride and magnesium fluoride were bombarded with 2.3 MeV alpha particles. The number of atoms of fluorine per cm2 as a function of the thickness of the targets and the target substrates were measured. The effect of substrate material on the measured number of atoms/cm2 of fluorine is negligible. © 1987 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division) All rights reserved.