The authors have measured the lifetime of metastable state (3s(4)P(5/2)) of F atoms by resonant laser-induced fluorescence method. For this experiment, a special 2.45 GHz electron cyclotron resonance (ECR) plasma source, which is highly efficient in F radical generation and free from magnetic field leakage in front of the beam-emitting orifice, has been developed. Using the ECR plasma gun, the authors observed a precision fluorescence spectrum related to 3p D-4(7/2)0(F=4) -> 3s(4)P(5/2)(F = 3) transition of F radicals, which made it possible to experimentally determine the longitudinal velocity distribution and the angular spread of the F radical beam. Based on these measured beam characteristics, the authors extracted a true decay curve of fluorescence intensity as a function of distance from the source and determined the-lifetime of F metastable state (3S (4)p(5/2)) as 7.3 +/-0.5 mu s. (c) 2006 American Vacuum Society.